merging ci branch

feat(hint): H2 Phase C batch 2 — DDL tier-3 hints (ADR-0053)
Per-form hints for the schema-shaping commands: create table, create m:n, add column/index/constraint, drop table/column/relationship/ index/constraint, rename column, change column (add_relationship was the Phase-B exemplar). Examples verified against the canonical usage templates. hint_ids wired on CREATE/CREATE_M2N/DROP/RENAME/CHANGE; catalogue + keys.rs registered. +2 spot tests (incl. multi-form DROP disambiguation); 2491 pass / 1 ignored, clippy clean.
2026-06-15 16:07:10 +00:00 · 2026-06-15 16:05:41 +00:00 · 2026-06-15 16:01:39 +00:00 · 2026-06-15 16:01:09 +00:00 · 2026-06-15 15:56:38 +00:00 · 2026-06-15 12:18:41 +00:00
54 changed files with 2948 additions and 424 deletions
@@ -0,0 +1,17 @@
+# Windows cross-link fix for the D1 release matrix (cargo-zigbuild).
+#
+# Rust's std links `-lsynchronization` on Windows (WaitOnAddress-based thread
+# parking). Rust normally satisfies this from the `self-contained` mingw libs
+# of its `rust-mingw` component — which rust-overlay does NOT ship — and Zig's
+# bundled mingw (used by `cargo zigbuild`) doesn't provide `libsynchronization.a`
+# either. The actual symbols are *forwarded by kernel32* (already linked), so an
+# empty stub import lib is enough to satisfy the linker. See `ci/winstub/`.
+#
+# These sections apply ONLY when building for the Windows targets, so host
+# builds (the gate's `cargo test`/`clippy`) and the Linux release targets are
+# unaffected.
+[target.x86_64-pc-windows-gnu]
+rustflags = ["-L", "native=ci/winstub"]
+
+[target.aarch64-pc-windows-gnullvm]
+rustflags = ["-L", "native=ci/winstub"]
@@ -0,0 +1 @@
+use flake
@@ -0,0 +1,65 @@
+# CI toolchain image for rdbms-playground.
+#
+# Purpose: a SMALL job-container image that
+#   (a) satisfies the Gitea act_runner job-container contract — /bin/sleep (the
+#       keep-alive entrypoint), bash (run: steps), node (JS actions such as
+#       actions/checkout); a bare nixos/nix image has none of these and won't
+#       even start (verified by the ci-probe run: "/bin/sleep: no such file"); and
+#   (b) carries the project's pinned nix toolchain with the flake's devShell
+#       pre-warmed, so CI runs `nix develop -c cargo ...` against a warm store.
+#
+# Base: node:22-bookworm-slim. Debian slim already provides bash + coreutils
+# (sleep); the node tag adds the actions runtime. Far smaller than the
+# catthehacker runner images (which bundle a whole GitHub-runner emulation we
+# don't need).
+FROM node:22-bookworm-slim
+
+# nix install + flake eval needs these. git because flakes prefer a VCS context
+# and tools shell out to it. Drop apt lists to keep the layer small.
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends \
+      curl xz-utils ca-certificates git \
+ && rm -rf /var/lib/apt/lists/*
+
+# Single-user nix (--no-daemon): store at /nix owned by root, no daemon/systemd
+# needed — the correct mode for a container. The official installer refuses root
+# and shells out to `sudo` purely to create /nix; pre-creating it ourselves (we
+# ARE root) sidesteps both. Enable flakes globally so every nix invocation (and
+# the runner's steps) get nix-command + flakes without flags.
+# nix.conf is written FIRST so the installer's own `nix-env` profile step reads
+# it: `build-users-group =` (empty) makes single-user nix build as the calling
+# user (root) instead of demanding the nixbld group/users a daemon install would
+# create; flakes are enabled globally in the same file.
+RUN mkdir -m 0755 /nix && chown root:root /nix \
+ && mkdir -p /etc/nix \
+ && printf 'build-users-group =\nexperimental-features = nix-command flakes\n' > /etc/nix/nix.conf \
+ && curl --proto '=https' --tlsv1.2 -sSf -L https://nixos.org/nix/install -o /tmp/nix-install.sh \
+ && sh /tmp/nix-install.sh --no-daemon \
+ && rm /tmp/nix-install.sh
+ENV PATH=/root/.nix-profile/bin:/nix/var/nix/profiles/default/bin:$PATH
+# We set PATH directly instead of sourcing the profile, so also point nix at the
+# Debian CA bundle (already installed) for substituter HTTPS — otherwise the
+# profile-provided NIX_SSL_CERT_FILE is missing and store downloads fail.
+ENV NIX_SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt
+
+# Warm the flake's devShell into the store: realizes nixpkgs + the pinned Rust
+# toolchain (rustc/cargo/clippy/rustfmt) + cargo-sweep. Only the inputs that
+# determine the shell are copied, so this expensive layer is cached and only
+# re-runs when the flake or the toolchain pin changes — not on every source edit.
+# (devShell eval is lazy: packages.default — and thus Cargo.toml/Cargo.lock — is
+# never forced here, so it needn't be present.)
+WORKDIR /warm
+COPY flake.nix flake.lock rust-toolchain.toml ./
+RUN nix develop -c rustc --version \
+ && nix develop -c cargo --version \
+ && nix develop -c cargo clippy --version \
+ && nix develop -c cargo fmt --version \
+ && nix develop -c cargo sweep --version
+WORKDIR /
+RUN rm -rf /warm
+
+# FOLLOW-UP optimisation (intentionally NOT done here, see CI notes): cargo
+# dependency + target caching. Each CI run still compiles the ~296-crate graph
+# from scratch and pulls crate sources from crates.io. A later pass can bake
+# `cargo fetch` (offline crate sources) and/or a warmed target dir, or wire
+# sccache, to cut run time. Correctness/first-green first; speed next.
@@ -0,0 +1,51 @@
+# Builds the nix CI toolchain image (.gitea/ci-image/Dockerfile) and pushes it
+# to the Gitea registry. The gate (ci.yaml) runs *inside* this image, so this
+# workflow is the gate's prerequisite. It only needs to run when the image's
+# inputs change — the Dockerfile, the flake, or the toolchain pin — plus on
+# manual dispatch.
+#
+# DinD pattern: plain docker:27-dind (one of the tested ci-test samples). No
+# registry proxy here — the runner's containers have direct internet egress
+# (the ci-probe run cloned github.com and pulled docker.io with no proxy), and
+# this image's RUN steps fetch from apt + nixos.org, which the proxy isn't
+# guaranteed to forward. The dind-cached:local + REGISTRY_PROXY_HOST variant is
+# a later speed optimisation for base-image pull caching, not needed for green.
+name: build-ci-image
+on:
+  push:
+    # Branch pushes only. Tag pushes ignore `paths:` filters and would rebuild
+    # the (unchanged) image on every release tag — `branches: ['**']` excludes
+    # tags, so this runs only when a branch push actually changes an image input.
+    branches: ['**']
+    paths:
+      - '.gitea/ci-image/Dockerfile'
+      - 'flake.nix'
+      - 'flake.lock'
+      - 'rust-toolchain.toml'
+      - '.gitea/workflows/build-ci-image.yaml'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ci-public
+    services:
+      docker:
+        image: docker:27-dind
+        options: --privileged
+        env:
+          DOCKER_TLS_CERTDIR: ""
+    env:
+      DOCKER_HOST: tcp://docker:2375
+      IMAGE: git.lazyeval.net/oli/rdbms-playground-ci
+    steps:
+      - uses: actions/checkout@v4
+      - name: wait for docker
+        run: until docker version >/dev/null 2>&1; do sleep 1; done
+      - name: registry login
+        run: |
+          echo "${{ secrets.REGISTRY_TOKEN }}" \
+            | docker login git.lazyeval.net -u "${{ secrets.REGISTRY_USERNAME }}" --password-stdin
+      - name: build
+        run: docker build -f .gitea/ci-image/Dockerfile -t "$IMAGE:latest" .
+      - name: push
+        run: docker push "$IMAGE:latest"
@@ -0,0 +1,39 @@
+# The CI gate. Runs inside the prebuilt nix toolchain image (built + pushed by
+# build-ci-image.yaml), so the pinned 1.95.0 toolchain is already warm — steps
+# just enter the flake devShell and run cargo.
+#
+# Gate = clippy + test. fmt is deliberately NOT gated yet (ADR-ci-002: the tree
+# isn't clean under stock rustfmt; revisit on main). The release job (static
+# binary for D2) and the platform matrix layer on later, step by step.
+name: ci
+on:
+  push:
+    # Branch pushes only — a tag push hits the same commit the branch push
+    # already gated, so `branches: ['**']` drops the redundant tag-triggered
+    # run (the release workflow owns tags). Pushing commits + a tag together
+    # still gates the commits via the branch push.
+    branches: ['**']
+    # Skip the gate for docs-only changes — markdown can't affect clippy/test.
+    # A push touching code *and* docs still runs (not all files are ignored).
+    # Note: flake/toolchain changes are NOT ignored — they can shift the
+    # toolchain and thus lint/test outcomes.
+    paths-ignore:
+      - 'docs/**'
+      - '**/*.md'
+  pull_request:
+    paths-ignore:
+      - 'docs/**'
+      - '**/*.md'
+
+jobs:
+  gate:
+    runs-on: ci-public
+    # Public package → anonymous pull, no credentials needed.
+    container:
+      image: git.lazyeval.net/oli/rdbms-playground-ci:latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: clippy (warnings denied)
+        run: nix develop -c cargo clippy --all-targets -- -D warnings
+      - name: test
+        run: nix develop -c cargo test --no-fail-fast
@@ -0,0 +1,95 @@
+# macOS release leg — the two *-apple-darwin binaries, built natively on the
+# Tart (Apple-Silicon) runner and attached to an existing Gitea release.
+#
+# Manual dispatch only: the Mac runner is intermittent, so this is triggered by
+# hand (with the Mac up) for a given release tag. The 4-target Linux/Windows
+# release (release.yaml) runs on the tag itself and never waits on the Mac, so a
+# release always has those four; the macOS two are added by dispatching this.
+#
+# NOTE: Gitea exposes workflow_dispatch only for workflows on the DEFAULT branch,
+# so this becomes triggerable once the CI work is merged to `main`.
+name: release-macos
+on:
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Release tag to build the macOS binaries for and attach to (e.g. v0.1.0)'
+        required: true
+
+jobs:
+  release-macos:
+    runs-on: macos
+    env:
+      NIX_CONFIG: "experimental-features = nix-command flakes"
+      TAG: ${{ inputs.tag }}
+      # Auto-provided by Gitea Actions; has repo write (release) scope.
+      TOKEN: ${{ secrets.GITEA_TOKEN }}
+      API: ${{ github.server_url }}/api/v1
+      REPO: ${{ github.repository }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.tag }}
+
+      - name: test
+        run: nix develop -c cargo test --no-fail-fast
+
+      - name: build, de-nix, sign, package + publish
+        run: |
+          set -e
+          mkdir -p dist
+          for t in aarch64-apple-darwin x86_64-apple-darwin; do
+            echo "==================== $t ===================="
+            nix develop -c cargo build --release --target "$t"
+            f="target/$t/release/rdbms-playground"
+
+            # Rewrite the nix-store libiconv load path to the system one, then
+            # re-sign ad-hoc (install_name_tool invalidates the signature; arm64
+            # requires a valid one). Guard against any remaining /nix/store dep.
+            for l in $(otool -L "$f" | awk '/\/nix\/store.*libiconv.*dylib/ {print $1}'); do
+              install_name_tool -change "$l" /usr/lib/libiconv.2.dylib "$f"
+            done
+            codesign --force --sign - "$f"
+            if otool -L "$f" | grep -q /nix/store; then
+              echo "ERROR: $t binary links a /nix/store dylib"; exit 1
+            fi
+
+            out="rdbms-playground-$TAG-$t"
+            cp "$f" "dist/$out"
+            ( cd dist && shasum -a 256 "$out" > "$out.sha256" )   # macOS: shasum, not sha256sum
+          done
+          ls -l dist
+
+          # Idempotent create-or-get the release (release.yaml likely created it
+          # already from the tag), then upload the two macOS binaries + checksums.
+          created=$(curl -sS -X POST "$API/repos/$REPO/releases" \
+            -H "Authorization: token $TOKEN" -H "Content-Type: application/json" \
+            -d "{\"tag_name\":\"$TAG\",\"name\":\"$TAG\",\"body\":\"Automated release for $TAG.\"}")
+          id=$(printf '%s' "$created" | node -e 'let s="";process.stdin.on("data",d=>s+=d).on("end",()=>{try{const o=JSON.parse(s);process.stdout.write(String(o.id||""))}catch(e){}})')
+          if [ -z "$id" ]; then
+            id=$(curl -sS "$API/repos/$REPO/releases/tags/$TAG" \
+              -H "Authorization: token $TOKEN" \
+              | node -e 'let s="";process.stdin.on("data",d=>s+=d).on("end",()=>{process.stdout.write(String(JSON.parse(s).id))})')
+          fi
+          echo "release id: $id"
+          for fa in dist/*; do
+            name=$(basename "$fa")
+            echo "uploading $name"
+            curl -sS -X POST "$API/repos/$REPO/releases/$id/assets?name=$name" \
+              -H "Authorization: token $TOKEN" -F "attachment=@$fa" > /dev/null
+          done
+          echo "published macOS assets for $TAG"
+
+      - name: prune nix store — keep the last 2 toolchain generations
+        # The runner wipes the workspace each run, so cargo target/ never
+        # accumulates. Bound the persistent nix store by generation: record the
+        # current devShell as a generation of a persistent profile (in $HOME),
+        # keep the 2 newest, reclaim what older ones referenced.
+        if: always()
+        run: |
+          echo "--- disk before ---"; df -h / | tail -1
+          P="$HOME/.cache/rdbms-ci/toolchain"
+          nix develop --profile "$P" -c true || true
+          nix-env -p "$P" --delete-generations +2 || true
+          nix-collect-garbage || true
+          echo "--- disk after ---"; df -h / | tail -1
@@ -0,0 +1,92 @@
+# Release: on a version tag, build the cross-platform binaries and publish them
+# to a Gitea release with checksums. Runs in the prebuilt CI image, so the
+# pinned toolchain + the release targets + cargo-zigbuild/zig are already warm.
+#
+# Matrix (D1, cross-built from Linux x86_64 via cargo-zigbuild):
+#   x86_64-unknown-linux-musl   aarch64-unknown-linux-musl   (static, D2)
+#   x86_64-pc-windows-gnu       aarch64-pc-windows-gnullvm   (standalone .exe)
+# macOS is deferred — its arboard/AppKit link needs Apple's SDK (see ADR-ci-001).
+# D3 package-manager manifests layer on later.
+#
+# Tests run once (host) before the matrix, so a tag can never publish untested
+# code, even one pointing at a commit that was never gated on a branch.
+name: release
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  test:
+    runs-on: ci-public
+    container:
+      image: git.lazyeval.net/oli/rdbms-playground-ci:latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: test
+        run: nix develop -c cargo test --no-fail-fast
+
+  build:
+    needs: test
+    runs-on: ci-public
+    container:
+      image: git.lazyeval.net/oli/rdbms-playground-ci:latest
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - x86_64-unknown-linux-musl
+          - aarch64-unknown-linux-musl
+          - x86_64-pc-windows-gnu
+          - aarch64-pc-windows-gnullvm
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: build
+        run: nix develop -c cargo zigbuild --release --target ${{ matrix.target }}
+
+      - name: package + publish
+        # Pin bash: the runner defaults scripted steps to dash, which rejects
+        # `set -o pipefail`. bash is in the CI image.
+        shell: bash
+        env:
+          TARGET: ${{ matrix.target }}
+          # GITEA_TOKEN is auto-provided with repo write (release) scope.
+          TOKEN: ${{ secrets.GITEA_TOKEN }}
+          API: ${{ github.server_url }}/api/v1
+          REPO: ${{ github.repository }}
+          TAG: ${{ github.ref_name }}
+        run: |
+          set -euo pipefail
+
+          # Windows targets produce a .exe; the rest a bare binary.
+          case "$TARGET" in *windows*) EXT=.exe ;; *) EXT= ;; esac
+          BIN="target/$TARGET/release/rdbms-playground$EXT"
+          OUT="rdbms-playground-$TAG-$TARGET$EXT"
+          mkdir -p dist
+          cp "$BIN" "dist/$OUT"
+          ( cd dist && sha256sum "$OUT" > "$OUT.sha256" )
+          ls -l dist
+
+          # Create the release for this tag; if a sibling matrix job already
+          # created it, look it up instead (idempotent + race-tolerant).
+          created=$(curl -sS -X POST "$API/repos/$REPO/releases" \
+            -H "Authorization: token $TOKEN" \
+            -H "Content-Type: application/json" \
+            -d "{\"tag_name\":\"$TAG\",\"name\":\"$TAG\",\"body\":\"Automated release for $TAG.\"}")
+          id=$(printf '%s' "$created" | node -e 'let s="";process.stdin.on("data",d=>s+=d).on("end",()=>{try{const o=JSON.parse(s);process.stdout.write(String(o.id||""))}catch(e){}})')
+          if [ -z "$id" ]; then
+            id=$(curl -sS "$API/repos/$REPO/releases/tags/$TAG" \
+              -H "Authorization: token $TOKEN" \
+              | node -e 'let s="";process.stdin.on("data",d=>s+=d).on("end",()=>{process.stdout.write(String(JSON.parse(s).id))})')
+          fi
+          echo "release id: $id"
+
+          for f in dist/*; do
+            name=$(basename "$f")
+            echo "uploading $name"
+            curl -sS -X POST "$API/repos/$REPO/releases/$id/assets?name=$name" \
+              -H "Authorization: token $TOKEN" \
+              -F "attachment=@$f" > /dev/null
+          done
+          echo "published $TARGET assets for $TAG"
@@ -2,6 +2,12 @@
 /target
 **/*.rs.bk

+# Nix
+# `nix build` output symlinks (`result`, `result-<name>`), direnv's cached env
+/result
+/result-*
+.direnv/
+
 # Snapshot test review files
 *.snap.new
 *.pending-snap
@@ -68,6 +68,12 @@ tempfile = "3.27.0"
 incremental = false
 debug = "line-tables-only"

+# Release builds back the distributed binaries (D2: single static binary).
+# strip = "symbols" drops the symbol table at link time so the shipped artifact
+# is lean (≈13 MB → 10 MB for the musl build) without a separate strip step.
+[profile.release]
+strip = "symbols"
+
 [lints.rust]
 unsafe_code = "forbid"
 unreachable_pub = "warn"
@@ -0,0 +1,30 @@
+# `ci/winstub/` — empty Windows import-lib stub
+
+`libsynchronization.a` here is an **empty `ar` archive** (8 bytes: `!<arch>\n`),
+referenced by `.cargo/config.toml` via `-L native=ci/winstub` for the Windows
+release targets.
+
+## Why
+
+The D1 release matrix cross-compiles Windows binaries from Linux with
+`cargo zigbuild` (see `docs/ci/adr/`). Rust's `std` links `-lsynchronization`
+for its `WaitOnAddress`-based thread parking. That import library is normally
+provided by Rust's `rust-mingw` "self-contained" component — which `rust-overlay`
+does not ship — and Zig's bundled mingw doesn't carry it either, so the link
+fails with:
+
+```
+error: unable to find dynamic system library 'synchronization'
+```
+
+The functions it would import (`WaitOnAddress`, `WakeByAddressSingle`,
+`WakeByAddressAll`) are **forwarded by `kernel32.dll`**, which is already linked,
+so they resolve at link and run time without a real `synchronization` import
+library. An **empty** stub is therefore sufficient: it satisfies the `-l`
+lookup and contributes no symbols.
+
+## Regenerating
+
+```
+zig ar rcs ci/winstub/libsynchronization.a
+```
@@ -0,0 +1 @@
+!<arch>
@@ -189,9 +189,18 @@ over keeping journaling coupled in the worker (which would have needed the
  no-op-skip / read-only sites no longer journal; success is journalled at
  the dispatch layer (`spawn_dsl_dispatch` / `run_replay` / app-command
  sites). The ring stays `Vec<String>`; `seed_history` / `ProjectSwitched`
-  are untouched. The vestigial worker `source` plumbing (the `_source`
-  param on `finalize_persistence` / `do_rebuild_from_text` and the thin
-  read-only `*_request` wrappers) is left in place — a clean follow-up.
+  are untouched. The vestigial worker `source` plumbing has since been
+  **fully unwound** (2026-06-14 follow-up): `_source` removed from
+  `finalize_persistence` / `do_rebuild_from_text`; the three read-only
+  `*_request` wrappers inlined and deleted; and — because the cascade ran
+  deeper than first estimated — the now-dead `source` param dropped from
+  the ~30 worker handlers (leaf + composite) that only forwarded it, plus
+  the `source` field removed from the `DescribeTable` / `QueryData` /
+  `RunSelect` requests and the matching `DatabaseHandle` method parameters
+  (the ~164 call-site churn was mostly tests). The only `source` left in
+  the worker is the snapshot/undo label (`snapshot_then` /
+  `stage_pre_mutation` / `begin_batch`), passed at the match-arm level.
+  Purely mechanical, compiler-guided, no behaviour change.
 - **App commands recall bare.** Because they are dispatched outside the
  `ExecuteDsl`/spawn path, app commands journal **simple** (`advanced =
  false`) at their own sites, and `submit` excludes them from the ring's
@@ -0,0 +1,404 @@
+# ADR-0053: Contextual `hint` — F1 live-input keybinding + `hint` command, with a tier-3 teaching corpus (H2)
+
+## Status
+
+Accepted — implementation in progress. Revised after a `/runda` review
+(2026-06-14): corrected the verbosity-default fact; re-keyed tier-3
+content off `help_id`; split the pre-submit-diagnostic and runtime-error
+paths; added a comprehensiveness coverage test. Revised again during
+Phase B implementation (2026-06-15): the first exemplar showed per-*node*
+keying is too coarse for multi-form commands (`add`/`drop`/`show`/
+`create`), so D3 now keys tier-3 content **per form** via a
+`hint_ids: &[&str]` array mirroring `usage_ids` — and **clause-concept
+hints** are recorded as a deferred extension (separate tracking issue).
+The parallel question of whether the in-app `help` command should
+likewise distinguish advanced-SQL forms is tracked **separately** as
+Gitea issue #36 (it touches shipped, ADR-backed `help` behaviour).
+
+Decided in conversation 2026-06-14. Closes the last open piece of **A1**
+(the canonical app-command set, ADR-0003): every app command is
+implemented except `hint`, which ADR-0003's command table listed as
+*"Request a hint for the current input (ADR pending)."* This ADR is that
+pending decision. Tracked as **H2** in `docs/requirements.md`.
+
+References ADR-0003 (app-command set + the `:` escape), ADR-0019 (the
+friendly error layer / H1), ADR-0021 (per-command usage templates / H1a),
+ADR-0022 (ambient typing assistance — colour + hint panel + completion),
+ADR-0027 (input validity indicator), ADR-0046 (sidebar navigation +
+responsive input hint), ADR-0049 (input-field readline keymap), and
+ADR-0051 (context/state-aware keybinding strip).
+
+## Context
+
+`hint` is the only unbuilt app command. The naive reading — "show a hint" —
+hides a real subtlety, and a real cost.
+
+**The subtlety: a submitted `hint` command cannot see live input.** App
+commands are submitted with Enter, which empties the input buffer. By the
+time `hint` dispatches, the partial command it was meant to help with is
+gone. So "a hint for the current input" cannot be served by a submitted
+command alone — it needs a *keybinding* that acts on the live buffer
+without submitting. ADR-0003 said "current input"; `requirements.md`
+broadened it to "current input **or the most recent error**." Both are
+wanted; they map to two different trigger surfaces.
+
+**The cost: the value of `hint` is content, not plumbing.** The app
+already carries two tiers of contextual text:
+
+- **Tier 1** — terse, always-on: syntax colour (ADR-0022); the error
+  *headline* alone (ADR-0019, when `messages_verbosity: Short`).
+- **Tier 2** — short contextual lines: the ambient typing prose /
+  `expected` set, shown live while typing (ADR-0022, catalogue
+  `hint.ambient_*` / `hint.value_slot_*`); and the error `hint:` field —
+  which, because `Verbosity::Verbose` is the **default**
+  (`src/friendly/translate.rs:46`), is shown **by default** beneath every
+  error headline (`messages short` is the opt-*out*, not `messages
+  verbose` the opt-in).
+
+So the verbose error hint is **already on screen by default**. If `hint`
+merely re-showed it, it would duplicate what the user can already see (and
+the ambient panel). To justify itself, `hint` must add a **tier 3**: a
+genuinely deeper, *teaching*-grade explanation — what the command/error
+means, a worked example, and the underlying relational concept. That
+corpus does not exist yet, and
+authoring it (to the standard of a teaching tool, where "pedagogy wins
+ties") is the bulk of the work.
+
+The mechanism is small and reuses everything already present: the command
+REGISTRY (`src/dsl/grammar/mod.rs`), the `AppCommand` enum
+(`src/dsl/command.rs`), key dispatch (`App::handle_key`,
+`src/app.rs:1155`), the `note_help`/`note_help_topic` renderers
+(`src/app.rs:2982`/`3021`), the parser/walker expected-set
+(`ParseError.expected`, `WalkResult.tail_expected`), the friendly
+catalogue + `t!` macro + `keys.rs` validation, and the output styling
+vocabulary (`OutputStyleClass::Hint`).
+
+## Decision
+
+### D1 — Two surfaces, no topic argument
+
+`hint` is delivered through **two complementary surfaces**:
+
+1. **F1 keybinding → live input.** Pressing **F1** while typing renders a
+   tier-3 hint for the command currently in the buffer, into the output
+   panel, **without submitting or altering the buffer**. This is the
+   primary, most-valuable path (it serves the literal "current input").
+2. **`hint` command → most recent error.** Submitting `hint` renders the
+   tier-3 expansion of the most recent error. This is why the command
+   exists despite the empty-buffer problem: the thing it helps with is
+   the *last thing you tried*, not the now-empty buffer.
+
+`hint` takes **no topic argument**. Explicit per-command reference is
+already `help <topic>` (H3); `hint` is purely *contextual*, which keeps
+the two cleanly distinct (`hint` = "help me with what I'm doing right
+now"; `help insert` = "show me the insert reference").
+
+F1 is a **read-only overlay**: it never alters the input buffer, the
+cursor, or the live completion memo (ADR-0022) — it only emits a block
+into the output journal. (It must therefore be handled in `handle_key`
+*before* the "any other key clears the memo" fall-through.)
+
+### D2 — Trigger matrix
+
+| Trigger | Buffer / state | Result |
+|---|---|---|
+| **F1** | non-empty input | tier-3 hint for the command being typed, plus the live "expected next" (from the walker's `tail_expected` / parser `expected`) |
+| **F1** | empty input, a recent error exists | tier-3 expansion of that error |
+| **F1** | empty input, no recent error | a short "getting started" pointer (press F1 while typing a command; `help` for the full list) |
+| **`hint`** (submitted) | a recent error exists | tier-3 expansion of that error (primary use) |
+| **`hint`** (submitted) | no recent error | the same "getting started" pointer |
+
+F1 is inert behind a modal and while a sidebar panel holds navigation
+focus (consistent with the existing `handle_key` gates, ADR-0046); it is
+active in the input context in both Simple and Advanced mode.
+
+**Two error sources, one namespace.** Errors come in two kinds and reach
+`hint` by different routes:
+
+- **Pre-submit diagnostics** (the ~33 `diagnostic.*` classes — arity,
+  type, unknown table/column) are computed *while typing* by the walker.
+  The **F1 live-input path** reads the current under-cursor diagnostic
+  directly from the walker (the same source the ambient panel uses) and
+  renders its `hint.err.<class>` block — no stored state needed.
+- **Runtime errors** (the 9 `translate_error` classes) occur *after*
+  submit. The **`hint` command / empty-input F1** path reads them via the
+  stored `last_error_hint_key` (D5).
+
+Both render from the same `hint.err.*` namespace. **`:`-prefix handling:**
+on the simple-mode one-shot escape (`: SELECT …`), command
+identification for the F1 path strips the leading `:` first, so the
+advanced form is matched.
+
+### D3 — The tier-3 content model
+
+Tier-3 blocks live in the friendly catalogue under the existing `hint:`
+top-level namespace (where tier-2 ambient strings already live), in two
+new sub-namespaces:
+
+- **`hint.cmd.<hint_id>`** — one per command **form**, keyed by a **new
+  `hint_ids: &'static [&'static str]`** field on `CommandNode`
+  (`src/dsl/grammar/mod.rs:512`), **mirroring the existing `usage_ids`**.
+  The F1 live-input path resolves the current input to its form's hint key
+  via `hint_key_for_input_in_mode`, which reuses the same form-word
+  disambiguation as `usage_key_for_input_in_mode`.
+
+  **Why an array mirroring `usage_ids`, not a per-node `hint_id`**
+  *(`/runda`/implementation revision, 2026-06-15)*: a single per-node key
+  is too coarse. Several entry words are **one node spanning many forms** —
+  `add` (column/relationship/index/constraint), `drop` (table/column/
+  relationship/index), `show` (data/table/tables/relationships/indexes),
+  `create` (table/index). A live-input hint for `add 1:n relationship` is
+  only useful if it is *specific to relationships*, so the content must be
+  **per form**, not per node. The project already solved exactly this for
+  usage templates (`usage_ids` is a per-form array, disambiguated by the
+  form word), so `hint_ids` mirrors it. Single-form nodes carry one entry;
+  multi-form nodes carry one per form. This also covers the advanced-SQL
+  forms whose `usage_ids` are empty (`SQL_INSERT/UPDATE/DELETE`,
+  `EXPLAIN_SQL`) — they get their own `hint_ids` directly, independent of
+  usage, with mode-correct SQL examples. (The `help`-list collapse of
+  advanced-SQL forms is a separate gap — issue #36.)
+
+  **Deferred extension — clause-concept hints** (issue #37): per-form is
+  the right granularity for tier-3 *teaching* (position-awareness within a
+  form is owned by tier-2 ambient + the live `Next:` line, D4). But some
+  **concepts live inside a clause**, not a form — `… on delete ⟨cascade|
+  set null|restrict⟩` (referential actions), the `create table` constraint
+  slots (`primary`/`unique`/`check`/`foreign`), `with pk`, `1:n`/`m:n`
+  cardinality. A learner parked in such a clause may want teaching deeper
+  than tier-2's candidate list but narrower than the whole-form block. v1
+  does **not** build this (it would multiply content for points whose value
+  we can't yet measure, and we don't expect to accumulate usage statistics
+  to drive it empirically — it will be tackled as a deliberate follow-up
+  job). The keying does not lock it out: a later `hint.concept.<topic>`
+  namespace can be surfaced when the cursor sits in a recognized clause,
+  layered on top of the per-form block.
+- **`hint.err.<class>`** — one per error/diagnostic class, keyed by the
+  friendly error/diagnostic key (e.g. `hint.err.foreign_key.child_side`,
+  `hint.err.type_mismatch`, `hint.err.insert_arity_mismatch`). Used by
+  both error routes (D2).
+
+Each tier-3 block is a **structured entry with three labelled parts**, so
+the voice stays consistent and the renderer can style them uniformly:
+
+```yaml
+hint.cmd.dsl.insert:
+  what: "Add one or more rows to a table."
+  example: "insert into Customers values ('Ann', 'ann@x.io')"
+  concept: "A row is one record; each value lines up with a column, in
+    order. Columns typed `serial`/`shortid` fill themselves — leave them out."
+```
+
+- **`what`** — one or two plain sentences: what this command does / what
+  this error means.
+- **`example`** — a single concrete, copyable line (rendered neutral, not
+  muted, so it stands out as runnable).
+- **`concept`** — the underlying relational idea, in teaching voice; the
+  part that makes this tier-3 rather than tier-2.
+
+`concept` is optional where there is genuinely no concept beyond the
+mechanics (e.g. `quit`); `what` + `example` are always present.
+
+### D4 — Rendering
+
+Both surfaces render through one new renderer, `App::note_hint*` (sibling
+of `note_help`/`note_help_topic`, `src/app.rs`), emitting a small framed
+block into the `output` buffer as `OutputKind::System` with
+`OutputStyleClass::Hint` on the `what`/`concept` prose and `Neutral` on
+the `example` line. The block is **persistent** (scrolls in the journal),
+unlike the transient ambient panel — pressing F1 is an explicit request
+to *keep* the deeper guidance on screen. The bottom keybinding strip
+(ADR-0051) advertises F1 in the editing/typing state.
+
+### D5 — "Most recent (runtime) error" state
+
+The **runtime-error route** (submitted `hint`, and empty-input F1) needs
+to map the last runtime error back to its `hint.err.<class>` key. Runtime
+errors today live only as rendered text in the `output` buffer. We add a
+single small piece of `App` state — **`last_error_hint_key:
+Option<String>`** — set at the `translate_error` call sites
+(`runtime.rs:2615`, `app.rs:2424`) when a friendly error is rendered,
+cleared when a later command succeeds. Absent → the "getting started"
+pointer.
+
+The **pre-submit-diagnostic route** (the F1 live-input path) needs no
+stored state: it reads the current diagnostic from the walker at F1 time
+(D2). This is the cleaner split the `/runda` pass surfaced — typing-time
+diagnostics and post-submit runtime errors are genuinely different
+sources and should not be funnelled through one stored key.
+
+### D6 — Content scope: comprehensive for v1
+
+v1 ships tier-3 content for the **whole inventory**, not a subset (the
+graceful tier-2 fallback below is a safety net, not the plan):
+
+- **~37 command forms** — every distinct node in `REGISTRY` gets its own
+  `hint.cmd.<hint_id>` block (app + DSL + DDL + advanced-mode SQL forms),
+  each with a **mode-correct example** (the advanced-SQL forms show SQL
+  syntax, their simple siblings show DSL — no sharing).
+- **9 runtime error classes** — `unique`, `foreign_key` (×4 sides),
+  `not_null`, `check`, `type_mismatch`, `not_found`, `already_exists`,
+  `generic`, `invalid_value` — each gets a `hint.err.*` block.
+- **~33 `diagnostic.*` pre-submit classes** — arity, type, unknown
+  table/column, etc. — each gets a `hint.err.*` block.
+
+The full enumerated checklist is the implementation plan's tracking
+artifact (see *Content inventory*, below).
+
+**Fallback (safety net):** if a tier-3 key is ever missing at runtime,
+the surface degrades to tier 2 — the ambient prose for the command path,
+or the verbose error `hint:` for the error path — never to a blank or an
+error. The `keys.rs` build-time validation keeps the corpus honest, so a
+missing key is caught in tests, not in front of a student.
+
+### D7 — Authoring process: exemplars-first
+
+Because the corpus is large and its *voice* is a pedagogical decision the
+maintainer owns, content is produced in two stages:
+
+1. This ADR carries **2–3 worked exemplars** (below) as the canonical
+   style reference. The `/runda` review of this ADR is where the voice and
+   depth are approved.
+2. Once approved, the remaining blocks are authored to that template in
+   **reviewable batches** (grouped by area: DDL, DML, app commands,
+   error classes), not one monolithic drop.
+
+### Exemplars (the style reference to approve)
+
+**Command (F1 live-input), `insert`:**
+
+```
+Hint — insert
+  What:    Add one or more rows to a table.
+  Example: insert into Customers values ('Ann', 'ann@x.io')
+  Concept: A row is one record; each value lines up with a column, in
+           order. Columns typed serial/shortid fill themselves — leave
+           them out.
+  Next:    a value list `(...)`, or `(col, ...) values (...)` to name columns
+```
+(The "Next:" line is the live expected-set from the walker, shown only on
+the non-empty-input F1 path.)
+
+**Error (`hint` command), foreign-key child-side violation:**
+
+```
+Hint — no parent row to point at
+  What:    The value you inserted into Orders.customer_id doesn't match
+           any Customers row, so the foreign key has nothing to point at.
+  Example: First   insert into Customers values ('Ann', ...)
+           Then    insert into Orders values (..., 'Ann')
+  Concept: A foreign key is a promise that every child points at a real
+           parent. The parent must exist first. To allow orphans on
+           delete instead, set the relationship's `on delete` to
+           `set null` or `cascade`.
+```
+
+**Command (F1 live-input), `add 1:n relationship`:**
+
+```
+Hint — add relationship
+  What:    Link two tables so a parent row can own many child rows.
+  Example: add 1:n relationship from Customers.id to Orders.customer_id
+  Concept: The "1:n" means one parent, many children. The child column
+           holds the foreign key; `--create-fk` adds it for you if it
+           doesn't exist yet.
+```
+
+## Forks (all user-chosen, 2026-06-14)
+
+- **Trigger model:** both a keybinding (live input) and a submitted
+  command (last error), rather than command-only or keybinding-only — the
+  live-input path is the most useful, but the command completes the A1
+  slot and serves the error case.
+- **Keybinding = F1:** the universal help convention; the key is
+  genuinely free (no `KeyCode::F(1)` binding exists today — the `"F1"`
+  strings in `input_render.rs`/tests are scenario labels, not the key, and
+  ADR-0022 uses no `F1` requirement label). No collision with the ADR-0049
+  readline keys, `Ctrl-O` (ADR-0046), `Esc`-clear, or the reserved
+  `Ctrl-C` cancel (I5). Rejected: `?` (a typeable character — fiddly
+  position-dependent handling) and a Ctrl/Alt chord (less discoverable, no
+  advantage).
+- **No topic argument:** contextual only; `help <topic>` already owns
+  explicit reference lookup.
+- **Comprehensive content for v1:** the full inventory, not a starter
+  subset.
+- **Exemplars-first authoring:** lock the voice on a few blocks, then
+  mass-author to template.
+
+## Consequences
+
+- **A1 closes.** With `hint` registered and built, all 15 canonical
+  app-level commands exist in both modes.
+- **A third contextual tier exists.** Students get on-demand, teaching-
+  grade guidance that is deeper than the always-on colour, the headline,
+  the ambient one-liner, and the verbose error hint — without cluttering
+  those terse defaults.
+- **One new keybinding (F1)** joins the keymap and the ADR-0051 strip.
+- **A new `hint_ids: &[&str]` field on `CommandNode`** (mirroring
+  `usage_ids`) + a `hint_key_for_input_in_mode` lookup (reusing the
+  `usage_key_for_input_in_mode` form-disambiguation), one new field of
+  `App` state (`last_error_hint_key`), and one new renderer family
+  (`note_hint*`); the `AppCommand` enum gains `Hint`, the grammar a `HINT`
+  node, the REGISTRY one entry.
+- **A large, durable content corpus** (~37 command blocks + ~42 error/
+  diagnostic blocks ≈ 80) enters the catalogue under `hint.cmd.*` /
+  `hint.err.*`, validated by `keys.rs`. This is ongoing surface area: new
+  commands/error classes should ship with their tier-3 hint (a checklist
+  item for future feature ADRs).
+- **Testing:** Tier-1 unit tests for the trigger matrix (F1 with
+  empty/non-empty input; `hint` with/without a recent error;
+  `last_error_hint_key` set on the `translate_error` sites and cleared on
+  success; the pre-submit-diagnostic vs runtime-error routing; the `:`
+  strip), the command-identification logic, and the tier-2 fallback;
+  Tier-2 `insta` snapshots for a representative rendered hint block;
+  Tier-3 integration tests for the end-to-end flows (type a partial
+  command → F1 → block appears, **buffer and completion memo untouched**;
+  run a failing command → `hint` → error expansion). **A
+  comprehensiveness coverage test** (enforces D6): iterate the REGISTRY
+  and assert every node has a `hint_id` resolving to a `hint.cmd.*` block,
+  and every runtime-error/diagnostic class has a `hint.err.*` block —
+  `keys.rs` only checks that *referenced* keys resolve, not that every
+  command/error *has* one, so this test is what makes "comprehensive"
+  enforceable rather than aspirational.
+
+## Out of scope
+
+- **Per-topic `hint <topic>`** — OOS (rejected): `help <topic>` already
+  serves explicit lookup; a topic arg would overlap it and double the
+  content-authoring surface.
+- **Re-showing tier-3 inline as the always-on ambient hint** — OOS
+  (rejected): the ambient panel stays terse by design (ADR-0022); tier-3
+  is on-demand. Promoting it would defeat the tiering.
+- **Localised tier-3 content beyond `en-US`** — OOS (deferred): the
+  catalogue is structured for i18n (ADR-0019), but additional locales
+  follow the project's English-only-for-v1 stance (requirements X2).
+- **`hint` for a *successful* command's deeper teaching** (e.g. "you just
+  created a table — here's what an index would add") — OOS (deferred): a
+  plausible future tier-3 use, but v1 scopes the command path to errors
+  and the F1 path to in-progress input.
+- **Clause-concept hints** (`… on delete ⟨action⟩`, constraint slots,
+  `with pk`, cardinality) — OOS (deferred, issue #37): a
+  `hint.concept.<topic>` layer surfaced when the cursor sits in a
+  recognized clause, deeper than tier-2's candidate list but narrower than
+  the per-form block. Per-form keying (D3) does not lock it out. To be
+  tackled as a deliberate follow-up job, not gated on usage statistics.
+
+## Content inventory (implementation tracking)
+
+The implementation plan enumerates and checks off every block:
+
+- **`hint.cmd.<hint_id>`** — one per distinct `REGISTRY` node (~37), each
+  with its own `hint_id` and a mode-correct example: app (`save`, `save
+  as`, `load`, `new`, `rebuild`, `export`, `import`, `replay`, `undo`,
+  `redo`, `mode`, `messages`, `copy`, `help`, `hint`, `quit`); DDL
+  (`create table`, `create m:n`, `add column`/`relationship`/`index`,
+  `drop`, `rename`, `change column`); DML (`insert`, `update`, `delete`,
+  `show`, `seed`, `explain`, `select`/`with`). The **7 advanced-mode SQL
+  forms** (`SQL CREATE TABLE`, `ALTER TABLE`, `CREATE/DROP INDEX`, `DROP
+  TABLE`, `SQL INSERT/UPDATE/DELETE`, `EXPLAIN SQL`, raw `SELECT`/`WITH`)
+  each get their **own** block with SQL syntax — they do **not** reuse
+  their simple sibling's (this is the `/runda` correction; the parallel
+  `help`-side gap is issue #36).
+- **`hint.err.*`** — one per runtime error class (`unique`,
+  `foreign_key.{child,parent}_side`, `not_null`, `check`,
+  `type_mismatch`, `not_found`, `already_exists`, `generic`,
+  `invalid_value`) and per `diagnostic.*` pre-submit class.
@@ -57,4 +57,5 @@ This directory contains the project's ADRs, recorded per
 - [ADR-0049 — Input-field readline keymap: Esc-clear + Ctrl-A/E/W/K/U (I1b)](0049-input-field-readline-keymap.md) — **Accepted + implemented 2026-06-12 (issue #29)**, closes Gitea **#29** and the deferred **I1b** readline requirement. **Amends ADR-0046**, which listed "readline shortcuts (I1b)" as out-of-scope — that item is now in scope and decided here; orthogonal to ADR-0003's input-*mode* model and extends the I1a single-line cursor editing already shipped. Binds, in the input field (non-modal, non-nav, both modes): **`Esc`** clears a partly-typed command (empty buffer, cursor→0, scroll→0); **`Ctrl-A`/`Ctrl-E`** alias Home/End (line start/end); **`Ctrl-W`** deletes the previous word (readline-style — eats trailing whitespace then the preceding non-whitespace run, UTF-8-safe on char boundaries, only back to the cursor); **`Ctrl-K`** kills to end of line; **`Ctrl-U`** kills to start. **Esc precedence:** a live Tab-completion memo still wins (Esc undoes the completion first, ADR-0022; Esc clears only when no memo) — Esc-once backs out the completion, Esc-again clears. Forks all user-chosen: **single-Esc-clears** (not double-Esc — discoverable over accident-proof; an unsubmitted draft can be lost, a submitted line is always in history); the **full I1b set** (not just the issue's literal Ctrl-A/E + Esc); a **new ADR** (not an ADR-0046 amendment / no-ADR). Cursor-only keys (Ctrl-A/E) leave history navigation intact like Home/End; buffer-mutating keys (Esc-clear, Ctrl-W/K/U) end it like Backspace. Helpers `clear_input`/`delete_prev_word`/`kill_to_end`/`kill_to_start` in `src/app.rs`; **22 new Tier-1 tests, 2458 pass / 0 fail / 0 skip (1 ignored), clippy clean**. OOS: on-screen keybinding hints (issue #27 owns surfacing per-focus keybindings in the bottom status line — this ADR makes the keys *work*, #27 makes them *discoverable*); demo-mode badges for the new chords (ADR-0047 follow-up — Esc already badges `[ESC]`, the glyph-less Ctrl-chords are flagged but not added); multi-line input (I1); word-wise cursor motion (Alt-B/F) / transpose / yank
 - [ADR-0050 — Incidental-DDL confirmations omit relationship info (structure-only)](0050-incidental-ddl-confirmations-omit-relationships.md) — **Accepted + implemented 2026-06-12 (issue #28)**, closes Gitea **#28**. **Supersedes** the incidental-DDL clause of **ADR-0044 §1** and the relationship-block half of **ADR-0016 §5**. Incidental-DDL confirmation echoes (`create table`, `add`/`drop`/`rename`/`change column`, `add`/`drop index`) now render **structure only** — header + column box + `Indexes:` + constraints — with **no `References:` / `Referenced by:` block** (neither prose nor diagram), even when the table carries relationships the user did not touch. Rationale (owner): a confirmation echo reports the change just made, not untouched relationships; ADR-0044's terse prose was the lesser of "prose vs diagram", but the right answer for these surfaces is **neither**. **Relationship-subject surfaces are unchanged** — `show table`, `add`/`drop relationship`, `show relationship` still render ADR-0044 diagrams; relationships appear only when the user asks for (`show table`) or acts on (`add`/`drop relationship`) one, and are one `show table <T>` away — **no information lost**. Forks both user-chosen: **scope = all incidental DDL** (not just `add column` — the rationale is uniform, the mental model clean, and it's the simpler edit) and **delete the prose renderer** (not retain it dormant — no dead code). **Mechanism:** the `handle_dsl_success` `matches!` routing is unchanged (relationship-subject → diagrams; else → `render_structure`); the change is one line inside `render_structure` (`output_render.rs` — drop the relationship-block call) since all its callers are incidental DDL, plus deletion of the orphaned `relationship_prose_lines` + `cols_disp` helpers. The prose format survives in ADR-0016 §5 + git history for a future OOS-7 always-prose setting. **Tests:** the prose-presence unit test + its snapshot removed; a new unit test asserts `render_structure` on a description carrying **both** inbound and outbound relationships emits the box but no prose; the misnamed `add_relationship_flow_shows_inbound_section_on_parent` integration test (which sent an `AddColumn`) inverted + renamed to assert the add-column echo omits the prose; the diagram tests (`show table`, `add relationship`) unaffected. **2458 pass / 0 fail / 0 skip (1 ignored), clippy clean**. `requirements.md` unaffected (ADR-tracked refinement of a decided area, like ADR-0044 itself)
 - [ADR-0051 — Bottom keybinding strip: context- and state-aware](0051-context-state-aware-keybinding-strip.md) — **Accepted + implemented 2026-06-13 (issue #27)**, closes Gitea **#27**. Repurposes the bottom status line into a **keystrokes-only, state-selected** strip (builds on ADR-0046 nav focus, ADR-0003 modes, ADR-0049 the #29 readline keys it now advertises, ADR-0022 the completion memo). A pure `status_bar_bindings(app) -> Vec<(key,label)>` chooses the strip by **priority, first match wins**: (1) **sidebar focus** → `Ctrl-O next pane · ↑↓/PgUp/PgDn scroll · Esc input`; (2) **completion memo live** (`last_completion`) → `Tab/Shift-Tab cycle · Esc cancel · Enter run`; (3) **history navigation** (new `App::is_browsing_history()` exposing the private `history_cursor`) → `↑↓ browse · Esc clear · Enter run`; (4) **editing** (input non-empty) → `Esc clear · Ctrl-A/E home/end · Ctrl-W del word · Enter run` (surfaces the #29 keys, closing ADR-0049's deferred advertisement); (5) **default** (empty) → `Ctrl-O sidebar · Tab complete · ↑ history · Enter run`. Priority is correct because Up clears the completion memo and Tab cancels history nav, so states 2/3 never co-occur, and the five are exhaustive for Input focus. **Typed-command words leave the strip** (`mode advanced`/`mode simple` switch, `:` one-shot) and **mode discovery moves to the empty-input hint** (`resolve_hint_lines`), **simple mode only**: `\`mode advanced\` for SQL` (the verb "type" omitted — the prompt implies it; advanced mode shows **no** pointer per a post-trial user decision — a switcher knows how they got there and `help` covers the way back). The one-shot's old `Backspace cancel one-shot` label is subsumed by the editing state (behaviour intact). Forks all user-chosen: **editing state shows the #29 keys** (vs unadvertised); **`Ctrl-C quit` omitted** from the strip (vs always shown); **no width-drop machinery** — the longest strip (~65 cols) fits all supported widths, so a **width-budget unit test** keeps it lean by construction instead (the user's own observation). Catalog: 12 new `shortcut.*` labels + the `panel.hint_mode_advanced` string added to `en-US.yaml`+`keys.rs` (validator-checked 1:1), 5 now-dead strip strings removed. **Modal-aware strip is OOS** (pre-existing: a modal owns the keyboard and carries its own hints; the strip under it is unchanged-in-kind, not worsened). Tests: 9 Tier-1 unit (per-state key sets — completion/history driven through real key events; width budget; mode-pointer presence/absence), 1 Tier-3 rewritten (`status_bar_is_keystroke_only_and_state_aware`), 15 full-panel snapshots re-accepted (reviewed — strip/hint only). **2467 pass / 0 fail / 0 skip (1 ignored), clippy clean.** OOS: modal-aware strip; a full-key cheatsheet overlay; Ctrl-K/U advertisement (editing strip shows the highest-value subset within the width budget)
- [ADR-0052 — Mode-tagged history for cross-mode recall](0052-mode-tagged-history-cross-mode-recall.md) — **Accepted + implemented 2026-06-13 (issue #30)**, closes Gitea **#30** — the feature (advanced history reusable in simple mode) **and** the bug in its comment (the `:` one-shot prefix lost across sessions). **Amends ADR-0034** (status field gains a `:adv` tag; **journaling moves from the worker to the dispatch layer**), **ADR-0015 §5/§6** (history.log leaves the worker transaction — `commit-db-last` now scopes yaml/csv/db only), and **ADR-0040** (a success-path journal-write failure is best-effort, not fatal); references ADR-0003. **Root cause:** history carried no mode, and the in-memory ring stored the raw `:select 1` while the worker journalled the *stripped* `select 1`, so the `:` was lost on disk. **Fix:** record the submission mode per entry as a **`:adv` suffix on the status token** (`ok`/`ok:adv`/`err`/`err:adv`) — `source` stays last + canonical so replay is unaffected; the in-memory ring (still `Vec<String>`) stores advanced entries in their `: `-prefixed simple-mode runnable form (a leading `:` unambiguously marks advanced since simple DSL never starts with `:`); recall **strips the `:` in advanced mode** (runs as bare SQL) and keeps it in simple mode (runs via the one-shot escape); hydration reconstructs the `: `-prefix from the tag, so cross-session = in-session. **The architectural turn (user's call):** the first draft kept journaling in the worker + threaded the mode down (~30-site plumbing); on review the user asked why the journal is written deep in the worker when the *failure* path already journals at the top of the chain — it shouldn't (history.log is a journal, not state). So **success journaling moved up** to `spawn_dsl_dispatch` / `run_replay` / the app-command sites (next to the failure path), the worker's `finalize_persistence` now writes only yaml/csv, and the journal write became **best-effort** (the command is already committed — consistent with the failure path; a rare disk-full leaves a committed command unjournalled, state intact). **App commands** journal simple (dispatched outside the spawn) and `submit` excludes them from the ring's advanced flag, so `undo`/`mode advanced` recall bare. Forks user-chosen: status-tag format (vs 4th field / `:`-in-source); unified scope; **dispatch-layer best-effort journaling** (vs worker-coupled-fatal). Two `/runda` passes (the second drove the relocation + app-command exclusion). Tests: the 15 worker-level journaling tests retired (worker no longer journals — yaml/csv/operation checks kept), re-covered at the new layer (history.rs status-tag + `:`-reconstruct; app.rs recall matrix; the #30 cross-session regression in `iteration6`; replay tests cover `run_replay` journaling). **2471 pass / 0 fail / 0 skip (1 ignored), clippy clean.** OOS: unwinding the now-vestigial worker `source` plumbing (`_source` params + thin `*_request` wrappers — a clean follow-up); replay re-journaling mode-fidelity (a replayed advanced line re-journals simple — not a regression)
+- [ADR-0052 — Mode-tagged history for cross-mode recall](0052-mode-tagged-history-cross-mode-recall.md) — **Accepted + implemented 2026-06-13 (issue #30)**, closes Gitea **#30** — the feature (advanced history reusable in simple mode) **and** the bug in its comment (the `:` one-shot prefix lost across sessions). **Amends ADR-0034** (status field gains a `:adv` tag; **journaling moves from the worker to the dispatch layer**), **ADR-0015 §5/§6** (history.log leaves the worker transaction — `commit-db-last` now scopes yaml/csv/db only), and **ADR-0040** (a success-path journal-write failure is best-effort, not fatal); references ADR-0003. **Root cause:** history carried no mode, and the in-memory ring stored the raw `:select 1` while the worker journalled the *stripped* `select 1`, so the `:` was lost on disk. **Fix:** record the submission mode per entry as a **`:adv` suffix on the status token** (`ok`/`ok:adv`/`err`/`err:adv`) — `source` stays last + canonical so replay is unaffected; the in-memory ring (still `Vec<String>`) stores advanced entries in their `: `-prefixed simple-mode runnable form (a leading `:` unambiguously marks advanced since simple DSL never starts with `:`); recall **strips the `:` in advanced mode** (runs as bare SQL) and keeps it in simple mode (runs via the one-shot escape); hydration reconstructs the `: `-prefix from the tag, so cross-session = in-session. **The architectural turn (user's call):** the first draft kept journaling in the worker + threaded the mode down (~30-site plumbing); on review the user asked why the journal is written deep in the worker when the *failure* path already journals at the top of the chain — it shouldn't (history.log is a journal, not state). So **success journaling moved up** to `spawn_dsl_dispatch` / `run_replay` / the app-command sites (next to the failure path), the worker's `finalize_persistence` now writes only yaml/csv, and the journal write became **best-effort** (the command is already committed — consistent with the failure path; a rare disk-full leaves a committed command unjournalled, state intact). **App commands** journal simple (dispatched outside the spawn) and `submit` excludes them from the ring's advanced flag, so `undo`/`mode advanced` recall bare. Forks user-chosen: status-tag format (vs 4th field / `:`-in-source); unified scope; **dispatch-layer best-effort journaling** (vs worker-coupled-fatal). Two `/runda` passes (the second drove the relocation + app-command exclusion). Tests: the 15 worker-level journaling tests retired (worker no longer journals — yaml/csv/operation checks kept), re-covered at the new layer (history.rs status-tag + `:`-reconstruct; app.rs recall matrix; the #30 cross-session regression in `iteration6`; replay tests cover `run_replay` journaling). **2471 pass / 0 fail / 0 skip (1 ignored), clippy clean.** replay re-journaling mode-fidelity (a replayed advanced line re-journals simple — not a regression). **Follow-up done 2026-06-14:** the vestigial worker `source` plumbing was fully unwound (compiler-guided, no behaviour change) — `_source` removed from `finalize_persistence`/`do_rebuild_from_text`, the three `*_request` wrappers inlined+deleted, the dead `source` param dropped from the ~30 forwarding worker handlers, and the `source` field removed from the `DescribeTable`/`QueryData`/`RunSelect` requests + their `DatabaseHandle` methods (~164 mostly-test call sites); the only worker `source` left is the snapshot/undo label (see ADR-0052 *Consequences*)
+- [ADR-0053 — Contextual `hint` command and keybinding](0053-contextual-hint-command-and-keybinding.md) — **Accepted, implementation in progress (2026-06-14; Phase A done, Phase B underway)**. Settles the `hint` slot ADR-0003 left "ADR pending"; closes the last open piece of **A1** and tracks requirements **H2**. **Two surfaces:** an **F1 keybinding** that renders a deep hint for the *live* partial input without submitting (the primary path — a submitted `hint` command can't see the buffer it would help with, since Enter empties it), and a submitted **`hint` command** that expands on the *most recent error*. **No topic argument** (contextual only — `help <topic>` already owns explicit reference). Introduces a **tier-3 teaching layer**, deeper than the existing tier-1 (colour / error headline) and tier-2 (ambient one-liner; and the error `hint:`, which is shown **by default** since `Verbosity::Verbose` is the default — `messages short` is the opt-*out*); without it `hint` would just duplicate what's already on screen. Tier-3 content lives in the catalogue under `hint.cmd.<hint_id>` (per command form) and `hint.err.<class>` (per error/diagnostic class), each a structured `what`/`example`/`concept` block rendered via a new `note_hint*` family with `OutputStyleClass::Hint`. **Keyed per-form via a new `hint_ids: &[&str]` field on `CommandNode` mirroring `usage_ids`** (revised in Phase B): a per-*node* key proved too coarse — `add`/`drop`/`show`/`create` are each one node spanning many forms, and a live-input hint for `add 1:n relationship` must be specific to relationships; `hint_key_for_input_in_mode` reuses `usage_key_for_input_in_mode`'s form-word disambiguation, and covers the advanced-SQL forms whose `usage_ids` are empty. Not keyed off `help_id` (it is `None` on the advanced-SQL nodes purely to dedup the `help` list; that parallel gap is issue **#36**). **Clause-concept hints** (`on delete` actions, constraint slots, `with pk`, cardinality) are a recorded **deferred extension** (`hint.concept.<topic>`, issue **#37**) — per-form is the right tier-3 granularity, with position-awareness owned by tier-2 + the live `Next:` line. Two error routes share `hint.err.*`: pre-submit `diagnostic.*` read live from the walker (F1 path), runtime `translate_error` classes via stored `last_error_hint_key` (`hint` command / empty-F1). Adds `AppCommand::Hint`, a `HINT` grammar node + REGISTRY entry, the `hint_ids` field, and `last_error_hint_key`; F1 is a read-only overlay (buffer + completion memo untouched). **Content is the bulk of the work** (the mechanism is ~a day): **comprehensive for v1** — ~37 command forms + 9 runtime error classes + ~33 `diagnostic.*` classes ≈ 80 teaching blocks — authored **exemplars-first** (voice approved in this ADR's `/runda` review, then mass-authored in batches), enforced by a **comprehensiveness coverage test** (every node/error class has a key), with graceful fall-back to tier-2 if a key is ever missing. Forks user-chosen: two-surface model; **F1** (vs `?` / a chord); no-arg; comprehensive scope; exemplars-first. OOS: per-topic `hint <topic>` (rejected — overlaps `help`); always-on tier-3 (rejected — keeps ambient terse); non-`en-US` locales + success-command teaching (deferred); the `help`-side advanced-SQL gap (issue #36)
@@ -0,0 +1,195 @@
+# ADR-ci-001: CI + release pipeline on Gitea Actions
+
+## Status
+
+**Accepted (2026-06-12); implemented the same day on the `ci` branch.** Every
+fork below was settled with the user as the pipeline was built, and each stage
+was verified live before acceptance:
+
+- a throwaway probe workflow established how the runner executes jobs;
+- the CI image was built and checked locally (runner contract, warm devShell);
+- the gate ran green (**clippy clean; 2424 tests pass / 0 fail / 1 intentional
+  ignored doctest**);
+- the release was exercised end-to-end — tag `v0.0.0-citest2` published a Gitea
+  release carrying the static binary (~10 MB) and its `.sha256`.
+
+This ADR records the **CI/release pipeline**. The **dev/build environment it
+runs on** — the nix flake (devShell + reproducible build, pinned Rust 1.95.0)
+— is **ADR-ci-002** (relocated here from main's ADR-0049); this ADR builds on
+it rather than restating it.
+
+> **Namespacing.** Kept in `docs/ci/adr/` (id `ADR-ci-001`), disjoint from
+> `main`'s integer ADR sequence, mirroring the website subproject's
+> `docs/website/adr/`. This avoids the cross-branch number collisions that
+> previously forced website ADRs to be renumbered (see that namespace's
+> history note and ADR-0000 "Numbering discipline").
+
+## Amendment — 2026-06-13: D1 matrix (non-macOS)
+
+§3 (Release) below describes the original **single-target** (x86_64 Linux) job.
+The release is now a **`test` → `build` matrix** over the four non-macOS D1
+targets (Linux + Windows × x86_64/aarch64), cross-built with `cargo-zigbuild`.
+The full decision — tooling, targets, the Windows `synchronization` stub, the
+matrix shape, and the macOS deferral with its licensing rationale — is recorded
+in its own record: **[ADR-ci-003](20260613-adr-ci-003.md)**.
+
+## Context
+
+The project is near feature-complete and needs CI (`requirements.md` **TT5**;
+the **CI** item in the deferred list) and a release path for its distributed
+binaries (**D1**/**D2**/**D3**). The self-hosted Gitea instance
+(`git.lazyeval.net`) has its Actions runner freshly set up — a first-time
+in-anger use — with a DinD-capable setup and a reusable `docker-build`
+template, exercised by a handful of sample workflows.
+
+The starting constraints, and what the probe found:
+
+- The runner label is **`ci-public`**. A throwaway probe
+  (`ci-probe.yaml`, since removed) established that **jobs run *inside* a
+  container** — `ghcr.io/catthehacker/ubuntu:act-22.04` by default, as **root**
+  — and therefore the runner *host's* nix is **not** on the steps' PATH
+  (`nix NOT on PATH`, `no /nix`). A custom job `container:` *can* be pulled
+  (it pulled `nixos/nix:latest`), but the runner keeps job containers alive
+  with `entrypoint: /bin/sleep` and runs JS actions (e.g. `actions/checkout`)
+  with `node`, so the container must provide **`sleep` + `bash` + `node`** —
+  a bare `nixos/nix` image has none and fails to start.
+- The reusable template only does `docker build`; it neither runs a Rust gate
+  nor pushes images nor uploads release assets — so a Rust pipeline can't just
+  call it.
+- The whole motivation (per the user) is for CI to use the project's **nix
+  flake** for its tools rather than relying on whatever the build machine has
+  — i.e. **one toolchain definition shared by dev and CI**.
+
+## Decision
+
+### 1. Toolchain delivery — a baked nix CI image
+
+CI gets its toolchain from a **purpose-built job-container image**, not from
+host nix and not by installing nix per-job:
+
+- **Base `node:22-bookworm-slim`.** Debian slim already provides `bash` +
+  coreutils (`sleep`); the `node` tag adds the actions runtime. This satisfies
+  the act_runner job-container contract at a fraction of the size of the
+  catthehacker runner images (chosen on the user's prompt to avoid those
+  multi-GB images), and far more reliably than a bare `nixos/nix` (which can't
+  start). `.gitea/ci-image/Dockerfile`.
+- **Single-user nix on top**, flakes enabled, with the **flake's devShell
+  pre-warmed** (`nix develop` realizes nixpkgs + the pinned Rust toolchain +
+  `cargo-sweep` + the musl cc into the store). CI then runs `nix develop -c …`
+  against a warm store — the *same* pinned toolchain as dev (ADR-ci-002),
+  reaching a ready toolchain in ~1.4 s.
+- **Built + pushed by `build-ci-image.yaml`** via the DinD service to the
+  Gitea container registry as `git.lazyeval.net/<owner>/rdbms-playground-ci`,
+  a **public** package (anonymous pull, no gate-side credentials). It runs only
+  when an image input changes (Dockerfile / `flake.nix` / `flake.lock` /
+  `rust-toolchain.toml`) or on manual dispatch.
+
+### 2. Gate — `ci.yaml`
+
+On branch pushes and PRs, a single job runs **inside the CI image**:
+`nix develop -c cargo clippy --all-targets -- -D warnings` then
+`nix develop -c cargo test --no-fail-fast`.
+
+**`fmt` is deliberately not gated.** The tree isn't clean under stock
+`rustfmt` (~100 files would change; no `rustfmt.toml` is committed) and
+reformatting would churn blame across the in-flight website branch and ongoing
+`main` work — so, by user decision, the gate is **clippy + test** and fmt is
+revisited on `main` (also recorded in ADR-ci-002).
+
+### 3. Release — `release.yaml`
+
+On a `v*` tag, one job in the CI image:
+
+1. **tests** (`cargo test`) — so a tag can never publish untested code, even
+   one pointing at a never-gated commit (user choice over relying solely on the
+   branch gate);
+2. **builds the static binary** for **`x86_64-unknown-linux-musl`** (D2:
+   single static binary, no runtime deps). The glibc/nix-store build is
+   non-portable; the musl target with `crt-static` is fully static. rusqlite's
+   `bundled` SQLite C is compiled by a **musl `cc`** (`pkgsCross.musl64`) wired
+   into the flake devShell via `CC_<target>` + `CARGO_TARGET_<TARGET>_LINKER`;
+   `[profile.release] strip = "symbols"` trims it (~13 MB → ~10 MB);
+3. **publishes** the binary + a `.sha256` to a Gitea release via the API and
+   the auto-provided **`GITEA_TOKEN`** — no third-party action (just `curl` +
+   `node`, both in the image).
+
+### 4. Triggers — branch vs tag hygiene
+
+- Gate and image-build are scoped to **branch** pushes (`branches: ['**']`).
+  Tag pushes ignore `paths:` filters and would otherwise spuriously rebuild the
+  unchanged image and re-gate an already-gated commit; the branch filter
+  excludes tags. **`release.yaml` owns tags** (`tags: ['v*']`).
+- Pushing commits + a tag together still gates the commits (via the branch
+  ref) and releases (via the tag ref) — no lost coverage, no duplicate runs.
+
+### 5. Auth
+
+- **Image push:** a dedicated PAT with `write:package`, supplied as the
+  `REGISTRY_USERNAME` / `REGISTRY_TOKEN` Actions secrets (the package owner
+  must match the token's user — an `oli`-namespace push with a different user
+  is refused with `reqPackageAccess`).
+- **Release publish:** the auto `GITEA_TOKEN` (repo/release scope).
+
+### 6. Scope this iteration — Linux x86_64, step by step
+
+The user's target is the full **D1** matrix, approached incrementally. This
+iteration ships **Linux x86_64 only**; the rest is deferred (below).
+
+## Consequences
+
+- **One toolchain, dev and CI.** They build through the same flake and cannot
+  drift. New image rebuilds only when the flake/toolchain/Dockerfile change.
+- **D2 is met on Linux.** The release artifact is a genuinely static,
+  stripped musl binary that runs with no runtime dependencies.
+- **DinD is per-job (no layer cache across runs),** so every `build-ci-image`
+  run rebuilds from scratch (~6 min). Acceptable at its trigger frequency;
+  base-pull caching via the `dind-cached` proxy variant is a possible later
+  optimisation.
+- **The CI image is ~5.5 GB+** (the Rust toolchain closure, now also musl).
+  Pulled once per runner and cached; slimming (multi-stage, prune) is optional.
+- **Every gate run recompiles the full dependency graph** (warm *toolchain*,
+  cold *deps*; clippy and test don't share artifacts), ~2 min total. Fine for
+  now; dependency/`target` caching is a deferred speed item.
+- **`GITEA_TOKEN` must retain release scope;** if an instance policy narrows
+  it, the release publish falls back to a repo-scoped PAT secret.
+
+## Alternatives considered
+
+- **Run on the runner host's nix.** Rejected — the probe showed steps run in a
+  container where host nix is unreachable.
+- **Install nix per-job in the default image.** Works but cold every run
+  (slow) and throwaway once the image exists; rejected in favour of the baked
+  image.
+- **`catthehacker` or bare `nixos/nix` as the base.** catthehacker is a
+  multi-GB runner emulation we don't need; bare `nixos/nix` lacks
+  `sleep`/`bash`/`node` and won't start. `node:22-bookworm-slim` is the small,
+  contract-satisfying middle (user's suggestion).
+- **A standard `rust:1.95` CI image instead of the flake.** Simpler in CI but a
+  *second* toolchain definition (drift) — counter to the unify-with-dev goal.
+- **A third-party Gitea release action.** Avoided; the API + auto token keep
+  the release self-contained and debuggable.
+
+## Deferred / out of scope (tracked, step by step)
+
+- **D1 matrix:** **macOS only** now (x86_64 + aarch64). The four non-macOS
+  targets shipped via cargo-zigbuild (see the 2026-06-13 amendment); macOS needs
+  Apple's SDK (osxcross + private SDK, or a Mac runner).
+- **D3 packaging:** Homebrew / Scoop / winget / `cargo-binstall` manifests
+  (and binstall-friendly asset naming/archives).
+- **Tier 4 (PTY E2E):** still unwired (`requirements.md` **TT4**); the gate runs
+  tiers 1–3 only, so **TT5** ("CI runs all tiers on Linux/macOS/Windows") is
+  partially met — Linux, tiers 1–3.
+- **CI speed:** dependency/`target` caching (cargo-chef into the image, or
+  `actions/cache`), and image slimming / `dind-cached` base-pull caching.
+- **Website deploy:** the static site → Cloudflare via Gitea Actions (a
+  separate, simpler workflow on the website branch).
+- **fmt gate:** revisit on `main` once a `rustfmt` style is chosen.
+
+## Relationship to other decisions
+
+- **Builds on ADR-ci-002** (nix flake dev + build env). This ADR adds the
+  musl-target/cc to that flake and consumes it from CI.
+- **Advances `requirements.md`:** **TT5** (CI runs the tiers — Linux, 1–3),
+  **D2** (static binary — Linux, done), **D1**/**D3** (partial/deferred).
+- **Mirrors the website subproject's** separate ADR namespace and its
+  static→Cloudflare-via-Gitea-Actions deployment posture (ADR-website-001).
@@ -0,0 +1,135 @@
+# ADR-ci-002: Nix flake for a reproducible dev + build environment
+
+## Status
+
+**Accepted (2026-06-12).** Implemented the same day on the `ci` branch:
+`flake.nix`, `flake.lock`, `rust-toolchain.toml`, `.envrc`. Verified
+end-to-end before acceptance — `nix develop` provides the pinned
+toolchain; `nix build .#default` produces a working binary; `cargo
+clippy --all-targets -- -D warnings` is clean and `cargo test` is
+**2424 passed / 0 failed / 1 ignored** (the ignored item is the
+intentional ```` ```ignore ```` doctest at `src/friendly/mod.rs:21`),
+all run *through the flake*. This ADR is the dev/build-environment
+foundation; the CI **pipeline** that consumes it (runner model, image,
+gate, release) is **ADR-ci-001**.
+
+> **History.** Created as **ADR-0049** in `main`'s integer ADR namespace
+> (`docs/adr/`); moved here to **ADR-ci-002** on 2026-06-12 to keep the
+> CI/dev-env decisions out of `main`'s sequence and end the cross-branch
+> number collision (`main` independently reaches for the next integer too —
+> the same problem the website subproject hit). Content is otherwise
+> unchanged. See ADR-0000 "Numbering discipline".
+
+## Context
+
+The project is near feature-complete and CI is finally being set up
+(`requirements.md` **TT5**, **CI** in the deferred list). CI must not
+depend on whatever Rust/toolchain happens to be installed on the build
+machine — that is neither reproducible nor honest about what the build
+needs.
+
+The sibling project **datamage** already solved this with a Nix flake
+(its ADR 0046): the flake is the single, version-pinned declaration of
+the toolchain, and both the dev shell and CI go through it so they
+cannot drift. We adopt the same pattern here. Ours is dramatically
+simpler than datamage's — this is a pure-Rust TUI with no Tauri /
+WebKitGTK / Node / WASM surface — so the flake carries almost no system
+dependencies.
+
+Two build facts drove the (tiny) dependency set, confirmed from
+`Cargo.lock`:
+
+- **`libsqlite3-sys` is built with `bundled`** → SQLite is compiled
+  from vendored C, which needs a C compiler. `nixpkgs`' `stdenv`
+  provides one automatically; nothing is declared for it.
+- **`arboard`'s clipboard backend is `x11rb`** — a pure-Rust socket
+  XCB client that links *no* C X11 libraries. So no X11/`pkg-config`
+  system inputs are needed to build or test. A live X server is only
+  required at *runtime* to actually copy; headless sessions fall back
+  to OSC 52.
+
+## Decision
+
+Adopt a **Nix flake** at the repository root as the canonical
+declaration of the dev *and* build environment.
+
+- **`flake.nix`** exposes two outputs (user-chosen 2026-06-12 over a
+  dev-shell-only variant):
+  - **`devShells.default`** — the pinned Rust toolchain (from
+    `rust-toolchain.toml` via `rust-overlay`) plus `cargo-sweep` for
+    the `target/` build-hygiene discipline (CLAUDE.md / the datamage
+    ADR 0050 equivalent).
+  - **`packages.default`** (= `packages.rdbms-playground`) — a
+    `rustPlatform.buildRustPackage` that produces the binary
+    reproducibly from the pinned toolchain and the committed
+    `Cargo.lock` (`cargoLock.lockFile` → `importCargoLock`, which
+    fetches each dependency by its lockfile checksum: offline,
+    deterministic, no `cargoHash` to churn). `nix build` yields the
+    artifact CI's gate/release can consume.
+- **`rust-toolchain.toml`** pins an **exact stable release**
+  (`1.95.0`), not the floating `stable` channel, so `nix flake update`
+  cannot surprise-bump Rust into new clippy lints that would fail the
+  `-D warnings` gate (same reasoning as datamage ADR 0046). Components:
+  `rustfmt` + `clippy`. No coverage/WASM tooling and no
+  cross-compilation targets yet — those are added when the release
+  matrix needs them, not before.
+- **`flake.lock`** pins every input (`nixpkgs` `nixos-26.05`,
+  `rust-overlay`, `flake-utils`) to a commit, making the env
+  bit-reproducible.
+- **`.envrc`** contains `use flake` for direnv auto-activation, kept
+  for parity with datamage even though direnv is not installed on the
+  current dev VM (entry is via `nix develop`).
+- **`packages.default` sets `doCheck = false`.** The test suite is
+  *not* run during `nix build` — the Nix build sandbox has no `HOME`
+  and no X server, which fights the project-directory / clipboard
+  paths the tests touch. Tests run as their own CI stage via
+  `nix develop -c cargo test`, keeping "build the artifact" and "run
+  the suite" cleanly separate.
+- **The package version is read from `Cargo.toml`** via
+  `builtins.fromTOML`, so it never drifts from the crate metadata.
+
+## Consequences
+
+- **One toolchain definition.** Dev and CI share the exact pinned
+  toolchain; they cannot drift. New contributors run `nix develop`
+  (or get auto-activation via direnv) and have the same Rust as CI.
+- **D2 (static binary) is unaffected and still pending.** The
+  `nix build` artifact links the Nix-store glibc *dynamically* — it is
+  a reproducible build/test artifact, **not** the single static
+  release binary D2 calls for. Release binaries will target a static
+  toolchain (e.g. `x86_64-unknown-linux-musl`) in the forthcoming CI
+  release work; that is a release-step concern, not a dev-shell one.
+- **`fmt` is deliberately *not* gated yet.** The tree is not clean
+  under stock `rustfmt` (~100 files would change; no `rustfmt.toml` is
+  committed and the code was shaped by something other than default
+  `rustfmt`). Reformatting churns blame across every file and would
+  conflict with the in-flight website branch and ongoing `main` work,
+  so — user decision 2026-06-12 — the `fmt` gate is left out for now
+  and revisited on `main`. The CI gate is `clippy` + `test`.
+- **Engine-name posture (CLAUDE.md) is respected.** The flake's
+  comments may name SQLite/`rusqlite` where technically necessary
+  (build-input rationale); no user-facing string is affected.
+
+## Alternatives considered
+
+- **Dev-shell only (no build package).** Matches datamage exactly; CI
+  would `cargo build` inside `nix develop -c`. Rejected (user choice):
+  a `nix build` package gives a reproducible release artifact straight
+  from the pinned toolchain, which the release job wants.
+- **A standard `rust:1.95` image in CI, flake for dev only.** Simpler
+  in CI (no nix-in-CI caching to solve), but it is a *second* place
+  that defines the toolchain — exactly the drift this ADR exists to
+  prevent. Rejected for the unified-env goal; the nix-in-CI caching
+  cost is solved in the CI pipeline work instead.
+- **`rustup` on the build machine.** The status quo CI would replace —
+  non-reproducible, machine-dependent, the thing we are eliminating.
+
+## Relationship to other decisions
+
+- Mirrors **datamage ADR 0046** (nix flake dev env) and its build
+  hygiene companion. This is the rdbms-playground analogue, scoped to
+  a pure-Rust project.
+- Feeds **ADR-ci-001** (the CI + release pipeline), which consumes this
+  flake for `requirements.md` **TT5** (CI runs the tiers) and the
+  **D1/D2/D3** distribution items (the release uses a static musl target
+  built through this flake).
@@ -0,0 +1,195 @@
+# ADR-ci-003: Cross-platform release builds (the D1 matrix)
+
+## Status
+
+**Accepted (2026-06-13); implemented the same day on the `ci` branch.** Every
+fork was settled with the user. Verified end-to-end:
+
+- all four targets cross-build locally from Linux x86_64;
+- the Linux binaries are statically linked (D2); the Windows artifacts are
+  valid PE32+ (x86-64 / Aarch64);
+- a real release-matrix run (tag `v.0.0.0-citest3`) published **8 assets** — the
+  four binaries + a `.sha256` each.
+
+**Runtime-verified (2026-06-13, by the user):** the **Linux x86_64** and
+**Windows aarch64** binaries launch and run correctly — one of each OS family
+and both architectures. The remaining two (**Linux aarch64**, **Windows
+x86_64**) are link-clean and valid format but not yet runtime smoke-tested.
+
+This ADR records the **cross-platform build strategy**; it sits on top of
+**ADR-ci-002** (the nix flake, which now carries the cross toolchain) and
+**ADR-ci-001** (the pipeline, whose release job this fills in).
+
+## Amendment — 2026-06-14: macOS implemented (closes D1)
+
+macOS is no longer deferred. The two `*-apple-darwin` targets now build on a
+**Tart (Apple-Silicon) macOS runner** registered to Gitea — building on **real
+Apple hardware** makes the SDK fully licensed, so the whole osxcross / SDK
+grey-area + public-image-redistribution problem (§5 below) simply **does not
+arise**. With all six D1 targets producing artifacts, **D1 is complete.**
+
+Details, all verified on the runner via a throwaway smoke-test before wiring the
+release leg:
+
+- **`release-macos.yaml`** — `workflow_dispatch` with a `tag` input,
+  `runs-on: macos`. The runner registered as `macos:host`, but `:host` is
+  act_runner's execution-backend schema (run on host, no container), **not** part
+  of the label, so the label is `macos`. Steps: `cargo test` (macOS gets the only
+  automated test coverage outside the Linux gate — user choice) → build both
+  darwin targets natively through the flake (`apple-sdk` added to the devShell so
+  the toolchain links AppKit) → **upload to the same release** via the idempotent
+  create-or-get.
+- **De-nix + re-sign.** The darwin stdenv bakes a `/nix/store` `libiconv` load
+  path into the binary (the *only* non-system dependency; everything else is
+  AppKit/Foundation/CoreGraphics/IOKit + `libSystem`/`libobjc`). The release step
+  rewrites it to `/usr/lib/libiconv.2.dylib` with `install_name_tool` and
+  **re-signs ad-hoc** (`codesign -f -s -`) — `install_name_tool` invalidates the
+  signature and Apple Silicon refuses an unsigned binary. A guard fails the build
+  if any `/nix/store` path remains. Result: portable, signed binaries (the native
+  one was confirmed to launch).
+- **Dispatch-only, intermittent runner.** The Mac isn't always on, so macOS is a
+  separate dispatched workflow (not a job in `release.yaml`) — a release always
+  carries the four Linux/Windows assets regardless of the Mac, and the two macOS
+  assets are added by dispatching `release-macos` for that tag. **Caveat:** Gitea
+  exposes `workflow_dispatch` only for workflows on the **default branch**, so
+  `release-macos` becomes triggerable once the CI work is merged to `main`.
+- **Cache hygiene (host-execution runner).** The runner wipes the workspace each
+  run, so cargo `target/` never accumulates; the persistent cache is the nix
+  store, bounded by **generation** — record the current devShell in a persistent
+  profile, keep the 2 newest generations (`nix-env --delete-generations +2`),
+  reclaim the rest. (The first sweep reclaimed a ~3.8 GB one-time backlog of
+  build scaffolding — source + build-only deps, not re-installed toolchains.)
+- **D2 on macOS.** macOS binaries cannot be fully static (`libSystem` is always
+  dynamic); "no runtime deps" there means *system libraries only*, which the
+  de-nix step guarantees.
+
+## Context
+
+`requirements.md` **D1** asks for binaries on **Linux, macOS, Windows × x86_64
+and aarch64** (six targets); **D2** asks for a **single static binary, no
+runtime deps**. The CI runner executes jobs in a **Linux x86_64** container
+(ADR-ci-001), so every target is **cross-compiled from Linux**.
+
+What's feasible is decided almost entirely by one dependency — **`arboard`**
+(the clipboard backend for the `copy` command). Its per-platform backends in
+`Cargo.lock`:
+
+| Target family | arboard backend | Needs a platform SDK to cross-link? |
+|---|---|---|
+| Linux x86_64 / aarch64 | `x11rb` (pure Rust) | No |
+| Windows x86_64 / aarch64 | `clipboard-win` + `windows-sys` (import libs bundled) | No |
+| **macOS x86_64 / aarch64** | **`objc2-app-kit` → links AppKit** | **Yes — Apple's SDK** |
+
+So **four targets cross-compile with no SDK**; **macOS is the hard wall** —
+AppKit can only be linked against Apple's SDK.
+
+## Decision
+
+### 1. Tooling — `cargo-zigbuild`
+
+Cross-compile with **`cargo-zigbuild`** (Zig's bundled clang + libc as a single
+universal cross `cc`/linker), added to the flake devShell alongside `zig`. One
+tool serves every non-macOS target, **including the `cc`-crate compile of
+rusqlite's bundled SQLite C**, with no per-target toolchain. It replaced the
+earlier single-target musl `cc` (ADR-ci-002's first cut).
+
+### 2. Targets this iteration — the four non-macOS
+
+Added to `rust-toolchain.toml` and the release matrix:
+
+- **`x86_64-unknown-linux-musl`**, **`aarch64-unknown-linux-musl`** — musl +
+  `crt-static`, so **fully static** portable binaries (D2);
+- **`x86_64-pc-windows-gnu`**, **`aarch64-pc-windows-gnullvm`** — Zig statically
+  links its libc, so the `.exe` is **standalone** (no mingw runtime DLLs).
+
+### 3. The Windows `synchronization` stub
+
+Rust's `std` links **`-lsynchronization`** (its `WaitOnAddress`-based thread
+parking). That import library is normally supplied by Rust's `rust-mingw`
+"self-contained" component — which **rust-overlay does not ship** — and Zig's
+mingw doesn't carry it either, so the link fails with *"unable to find dynamic
+system library 'synchronization'"*. The functions (`WaitOnAddress`,
+`WakeByAddress*`) are **forwarded by `kernel32`** (already linked), so an
+**empty stub** `libsynchronization.a` (committed at **`ci/winstub/`**, 8 bytes,
+wired via **`.cargo/config.toml`** for the Windows targets *only*) satisfies the
+linker without contributing symbols. Host and Linux builds are untouched by it.
+
+### 4. Workflow shape — test once, then a build matrix
+
+`release.yaml` is **`test` → `build`**:
+
+- **`test`** runs once on the host (`cargo test`) — a tag never publishes
+  untested code;
+- **`build`** is a **matrix over the four targets** (`needs: test`,
+  `fail-fast: false`), each `cargo zigbuild --release --target <triple>`, then
+  packages the binary (`.exe` for Windows) + a `.sha256` and uploads both to the
+  **shared release** via an **idempotent create-or-get** (the first matrix job
+  creates the release; the rest fetch it).
+
+### 5. macOS — deferred, with rationale
+
+macOS is **not** in this iteration. `arboard`→AppKit needs the macOS SDK, and:
+
+- the SDK ships **only inside Xcode**; Apple's license ties its use to
+  **Apple-branded hardware**, so using it on a Linux runner is a **grey area**
+  (widely done, low enforcement, but technically against the terms);
+- **redistributing** the SDK is a clearer violation — and our **CI image is
+  public**, so the SDK **cannot be baked into it** even if the grey area were
+  accepted; it would have to live in a private store;
+- the **clean** path is building on **real Apple hardware** (a Mac registered as
+  a Gitea runner, or hosted Mac CI), where the SDK is fully licensed.
+
+macOS therefore becomes its **own step**, choosing between **(a)** osxcross + a
+**private** SDK kept out of the public image, or **(b)** a **Mac runner**. The
+user decides when we get there.
+
+## Consequences
+
+- **D1: four of six targets met** from a single Linux runner; **D2 met on
+  Linux** (static musl). Windows `.exe`s are standalone.
+- **Runtime coverage:** Linux x86_64 + Windows aarch64 confirmed running
+  (user, 2026-06-13); Linux aarch64 + Windows x86_64 are the outstanding
+  runtime checks.
+- **Each matrix target recompiles from scratch** (~2–4 min; ~10 min total on the
+  single runner), and Zig's per-target libc cache is cold each run. Fine at
+  release frequency; cacheable later if it matters.
+- **The empty stub depends on `kernel32` forwarding `WaitOnAddress`** (true on
+  Windows 8+), which covers every supported target.
+- **Asset naming** `rdbms-playground-<tag>-<target>[.exe]` is close to what
+  `cargo-binstall` / the D3 package managers will want.
+
+## Alternatives considered
+
+- **`cross` (cross-rs).** Docker-image-per-target; covers Linux + Windows but
+  **not macOS** (no legally redistributable Apple images), and needs DinD
+  orchestration inside our job. Rejected — no macOS, more moving parts than
+  zigbuild.
+- **Per-target nix cross (`pkgsCross`).** Clean for Linux-musl and
+  Windows-x86_64 (mingw-w64, which *does* ship `libsynchronization.a`), but
+  Windows-aarch64 isn't readily packaged and **macOS-from-Linux is unsupported**
+  in nixpkgs. Rejected — incomplete.
+- **Native runners per OS.** Cleanest for macOS/Windows, but needs mac/windows
+  runners we don't have. Kept on the table specifically for the deferred macOS
+  step.
+- **A real `libsynchronization.a`** (from nixpkgs mingw or a `rust-mingw`
+  component) instead of the empty stub. More principled, but more flake
+  machinery, doesn't cover Windows-aarch64, and unnecessary — the stub links
+  clean because the symbols resolve via `kernel32`.
+
+## Deferred / out of scope
+
+- ~~**macOS** (x86_64 + aarch64)~~ — **done** via the Tart runner (see the
+  2026-06-14 amendment); §5 below is the as-deferred rationale, kept for history.
+- **D3 packaging** — Homebrew / Scoop / winget / `cargo-binstall` manifests
+  (and binstall-friendly archive naming).
+- **CI speed** — caching per-target builds / Zig's libc cache.
+- **Runtime smoke test** of the two not-yet-checked targets (Linux aarch64,
+  Windows x86_64).
+
+## Relationship to other decisions
+
+- **Extends ADR-ci-002** — the flake devShell now carries `cargo-zigbuild` +
+  `zig` and the four release targets.
+- **Fills in ADR-ci-001 §3 (Release)** — that single-target job is now this
+  matrix.
+- **Advances `requirements.md`** **D1** (4/6) and **D2** (Linux, done).
@@ -0,0 +1,23 @@
+# CI / Build Architecture Decision Records
+
+Decision records for the **continuous-integration + release pipeline**
+subproject — the Gitea Actions workflows under `.gitea/`, the nix CI image,
+and the release tooling. These are kept in their own namespace, separate
+from the project-wide ADRs in [`docs/adr/`](../../adr/README.md), so CI
+decisions never compete with the main global ADR sequence for numbers — the
+same split the website subproject uses (`docs/website/adr/`, on the `website`
+branch), and for the same reason (see
+[ADR-0000 "Numbering discipline"](../../adr/0000-record-architecture-decisions.md)).
+
+**Numbering.** Files are named `<date>-adr-ci-<NNN>.md` and referenced in
+prose as `ADR-ci-NNN`. The `<date>` (the ADR's accepted/created day,
+`YYYYMMDD`) plus the `ci` segment keeps the namespace disjoint from `main`'s
+integers. Assign the next free `NNN` from this index. Every ADR change
+updates this index in the same edit (the ADR-0000 index-upkeep rule applies
+here too).
+
+## Index
+
+- [ADR-ci-001 — CI + release pipeline on Gitea Actions](20260612-adr-ci-001.md) — **Accepted 2026-06-12** (implemented the same day on the `ci` branch). Establishes the CI/release pipeline on the self-hosted Gitea instance's Actions runner (`ci-public`). **Runner model** (established by a throwaway probe): jobs execute *inside* a container (`catthehacker/ubuntu:act-22.04` by default), as root, so the runner host's nix is **not** reachable from steps. **Toolchain delivery:** a **baked CI image** — `node:22-bookworm-slim` (satisfies the act_runner job-container contract: `/bin/sleep` keep-alive, `bash`, `node` for JS actions; a bare `nixos/nix` image lacks these and won't start) **+ single-user nix + the flake's devShell pre-warmed** — built by `build-ci-image.yaml` via DinD and pushed to the Gitea container registry as a **public** package, so CI runs `nix develop -c …` against the **same pinned toolchain as dev** (the flake, ADR-ci-002) with a warm store (~1.4 s to a ready toolchain). **Gate** (`ci.yaml`): `clippy -D warnings` + `cargo test` inside that image on branch pushes + PRs; **fmt deliberately not gated** (the tree isn't stock-rustfmt-clean — user decision, revisit on `main`; see ADR-ci-002). **Release** (`release.yaml`): on a `v*` tag, runs the tests, builds the **static `x86_64-unknown-linux-musl` binary** (D2: single static binary, no runtime deps — the glibc/nix build is non-portable), strips it, and publishes it + a `.sha256` to a Gitea release via the API and the auto-provided `GITEA_TOKEN`. **Triggers:** gate + image-build are scoped to **branch** pushes (`branches: ['**']`) so a release tag doesn't spuriously re-run them; the image-build additionally path-filters to its inputs (Dockerfile/flake/toolchain); the release owns tags. **Auth:** a dedicated PAT (`REGISTRY_USERNAME`/`REGISTRY_TOKEN` secrets) pushes the image; the auto `GITEA_TOKEN` publishes releases. **Scope:** the original release job was Linux x86_64 only; it's now the **four non-macOS D1 targets** (Linux + Windows × x86_64/aarch64) cross-built via cargo-zigbuild — see **ADR-ci-003**. macOS, D3 package-manager manifests, CI-speed dependency caching, and the website's static→Cloudflare deploy remain deferred, added step by step. Verified live: probe → runner facts; image built + checked locally; gate green (**2424 tests**); release exercised end-to-end (`v0.0.0-citest2` published with binary + checksum). Builds on **ADR-ci-002** (the nix flake, relocated here from main's ADR-0049 to avoid exactly this cross-branch collision).
+- [ADR-ci-002 — Nix flake for a reproducible dev + build environment](20260612-adr-ci-002.md) — **Accepted 2026-06-12** (relocated from main's **ADR-0049** on the same day — content unchanged — to keep CI/dev-env decisions out of `main`'s integer sequence). The single, version-pinned declaration of the **dev *and* build toolchain** so CI never relies on whatever Rust is on the build machine — mirroring **datamage ADR 0046**, but far simpler (pure-Rust TUI). Root **Nix flake** with two outputs: **`devShells.default`** (pinned **Rust 1.95.0** via `rust-toolchain.toml` + `rust-overlay`, `cargo-sweep`, and the musl cc for the static release build) and **`packages.default`** (`rustPlatform.buildRustPackage` from the committed `Cargo.lock`; `doCheck = false`). Exact-pin (not floating `stable`) so `nix flake update` can't surprise-bump clippy past the `-D warnings` gate. System inputs near-empty by design (`libsqlite3-sys bundled` → stdenv cc only; `arboard`→`x11rb` pure-Rust). `.envrc` (`use flake`) for direnv parity. Verified through the flake: `nix build` yields a working binary, clippy clean, **2424 tests pass / 0 fail / 1 intentional ignored doctest**. Consumed by **ADR-ci-001** (the pipeline). Alternatives rejected: dev-shell-only; a standard `rust:1.95` CI image (a second toolchain definition = drift); `rustup` on the build host (non-reproducible).
+- [ADR-ci-003 — Cross-platform release builds (the D1 matrix)](20260613-adr-ci-003.md) — **Accepted 2026-06-13** (implemented + a real matrix release verified the same day — tag `v.0.0.0-citest3` published 8 assets). Cross-compiles the **four non-macOS D1 targets** from the Linux x86_64 runner with **`cargo-zigbuild`** (Zig's bundled clang + libc as one universal cross cc/linker, incl. rusqlite's bundled SQLite C; added to the flake devShell, replacing the single-target musl cc): **`x86_64`/`aarch64-unknown-linux-musl`** (musl + crt-static → fully static, **D2**) and **`x86_64-pc-windows-gnu`** / **`aarch64-pc-windows-gnullvm`** (Zig statically links libc → standalone `.exe`). **Windows `synchronization` stub:** Rust std links `-lsynchronization` (WaitOnAddress thread-parking), an import lib rust-overlay's toolchain doesn't ship and Zig's mingw lacks; the symbols are forwarded by `kernel32`, so an **empty 8-byte stub** `libsynchronization.a` (`ci/winstub/`, wired via `.cargo/config.toml` for the Windows targets only) satisfies the linker. **Workflow:** `release.yaml` = **`test` once (host) → `build` matrix** over the four targets (`needs: test`, `fail-fast: false`); each job packages binary (`.exe` for Windows) + `.sha256` and uploads to the **shared release** via idempotent create-or-get. **macOS** (2026-06-14 amendment) — built natively on a **Tart (Apple-Silicon) runner** (`runs-on: macos`), which makes the SDK fully licensed and dissolves the grey-area/public-image problem; `release-macos.yaml` is **dispatch-only** (intermittent runner; becomes triggerable once CI is on `main`), de-nixes the binary's libiconv load path (`install_name_tool` → `/usr/lib`) + re-signs ad-hoc, and uploads to the tagged release. **D1 complete (all six targets).** Alternatives rejected: `cross` (no macOS, needs DinD), per-target nix cross (Windows-aarch64 unpackaged, macOS-from-Linux unsupported), a real `libsynchronization.a` (more machinery, doesn't cover Windows-aarch64). Runtime-verified by the user (2026-06-13): Linux x86_64 + Windows aarch64 run correctly; Linux aarch64 + Windows x86_64 are the outstanding runtime checks. Builds on ADR-ci-002 (flake) and fills in ADR-ci-001 §3 (Release).
@@ -0,0 +1,243 @@
+# Plan — ADR-0053: contextual `hint` command + F1 keybinding (H2)
+
+Implements ADR-0053. Closes the last open piece of **A1** (the canonical
+app-command set) and requirements **H2**. No Gitea issue — this is
+requirements-driven work; any genuine "later" item found en route gets
+its own issue (cf. #36, already filed for the parallel `help`-side gap).
+
+## 1. Goal
+
+Give learners on-demand, **teaching-grade** contextual help — a *third*
+tier beneath the existing terse always-on text (tier 1) and the
+short contextual lines that are already shown (tier 2: the live ambient
+prose, and the error `hint:` which is on by default since
+`Verbosity::Verbose` is the default). Two surfaces:
+
+- **F1** (read-only overlay) → a tier-3 block for the **live partial
+  input**, or — on empty input — for the **most recent runtime error**.
+- **`hint`** (submitted app command) → the tier-3 block for the **most
+  recent runtime error** (the buffer is empty post-submit, so it can only
+  act on recent context).
+
+The mechanism is small; the **content corpus is the feature** (~80
+blocks, comprehensive for v1, authored exemplars-first per ADR-0053 D7).
+
+## 2. The shape of the work (why this order)
+
+The mechanism and the content are separable, and the mechanism should
+land first with **graceful tier-2 fallback** so every surface works
+before any tier-3 text exists. That lets us:
+
+- build + test the trigger matrix / routing / `:`-strip / read-only-
+  overlay behaviour against a skeleton (TDD), then
+- pour in content in reviewable batches without re-touching the wiring,
+- and turn on the **comprehensiveness coverage test** only once the
+  corpus is complete (it is red until then — by design).
+
+Build order: **Phase A** (mechanism skeleton, falls back to tier-2) →
+**Phase B** (catalogue structure + the three approved exemplars) →
+**Phase C** (comprehensive content, batched) → **Phase D** (polish:
+strip advertisement, snapshots, full green).
+
+## 3. Grammar: the `hint_ids` field + the `HINT` node
+
+### 3a. New `CommandNode.hint_ids` (per-form — revised in Phase B)
+- Add `pub hint_ids: &'static [&'static str]` to `CommandNode`
+  (`src/dsl/grammar/mod.rs:512`, beside `help_id` / `usage_ids`),
+  **mirroring `usage_ids`** — *not* a per-node `Option<&str>`. The Phase-B
+  exemplar (`add 1:n relationship`) showed per-*node* keying is too coarse:
+  `add`/`drop`/`show`/`create` are each one node spanning many forms, and
+  a live-input hint must be specific to the typed form. Compiler forces
+  every node literal (~37, across `grammar/app.rs`, `data.rs`, `ddl.rs`) to
+  set it — Phase A/B leave most `&[]` (tier-2 fallback); Phase C fills them.
+  **Multi-form nodes list ALL their form keys** (e.g. `add` →
+  `["add_column", "add_relationship", "add_index", "add_constraint"]`) so
+  the form-word disambiguation resolves correctly and unauthored forms fall
+  back at render rather than mis-resolving to a sibling.
+- **Lookup:** `hint_key_for_input_in_mode(source, mode)` returns the single
+  typed form's hint stem, reusing `pick_form_key` (factored out of
+  `usage_key_for_input_in_mode` — shared digit/`m:n`/suffix disambiguation).
+- **Why a new field, not `help_id`** (ADR-0053 D3): `help_id` is `None` on
+  the 7 advanced-SQL forms purely to dedup the `help` *list*; those forms
+  have distinct SQL syntax and need their own block. `hint_ids` is per
+  form. (The parallel `help`-side gap is issue #36; clause-concept hints
+  are deferred — issue #37.)
+
+### 3b. `AppCommand::Hint` + the `HINT` node
+- `AppCommand::Hint` variant (no fields — no topic arg) in
+  `src/dsl/command.rs:544`.
+- `pub static HINT: CommandNode` in `grammar/app.rs` mirroring `HELP` but
+  with **no topic shape** (bare keyword, like `UNDO`): `entry:
+  Word::keyword("hint")`, `shape: EMPTY_SEQ` (as `UNDO`,
+  `grammar/app.rs:333`), `ast_builder:
+  build_hint` (returns `Command::App(AppCommand::Hint)`), `help_id:
+  Some("app.hint")`, `hint_id: Some("app.hint")`, `usage_ids:
+  &["parse.usage.hint"]`.
+- Register `(&app::HINT, CommandCategory::Simple)` in `REGISTRY`
+  (`grammar/mod.rs`), beside `HELP`. (App commands are available in both
+  modes via the existing mechanism.)
+
+## 4. Command identification (live-input → node)
+
+The F1 live-input path needs "which command form is being typed." **The
+lookup machinery already exists** — do not rebuild entry matching:
+- `command_for_entry_word(word) -> Option<(usize, &'static CommandNode)>`
+  (`grammar/mod.rs:811`) returns the matched node for an entry word
+  (Simple-first; the caller extracts the first word of the input).
+- `usage_keys_for_input_in_mode(source, mode)` (`grammar/mod.rs:564`)
+  already performs the **mode-aware** Simple/Advanced selection the hint
+  path needs (advanced `create` → the SQL nodes, simple → the DSL node) —
+  it just returns `usage_ids` rather than the node.
+- **The only new bit:** a thin `hint_id_for_input_in_mode(source, mode)`
+  (or a node-returning sibling of `usage_keys_for_input_in_mode`) that
+  applies the same mode selection and returns the chosen node's
+  `hint_id`. Mirror the existing function; don't duplicate its matching.
+- **`:`-strip:** in Simple mode, strip a leading `:` (one-shot escape,
+  ADR-0003) before identification so `: SELECT …` resolves to the
+  advanced `SELECT` node.
+- No match (empty / unrecognised entry word) → the "getting started"
+  pointer (D2).
+
+## 5. F1 keybinding (read-only overlay)
+
+In `App::handle_key` (`src/app.rs:1155`):
+- Add an F1 arm (`KeyCode::F(1)`) **after** the modal gate and the
+  sidebar-nav gate (inert there, per D2), and **before** the
+  "any other key clears the completion memo" fall-through (`_ =>
+  self.last_completion = None`, ~line 1228) — F1 must **not** clear the
+  memo or touch the buffer/cursor (D1).
+- Behaviour (the trigger matrix, D2):
+  - non-empty input → `note_hint_for_input()` (the command's `hint.cmd`
+    block + the live "Next:" expected-set from the walker).
+  - empty input + `last_error_hint_key` set → `note_hint_for_error()`.
+  - empty input + no recent error → `note_getting_started()`.
+- Returns `Vec::new()` (pure output emission, like `help`).
+- `demo_badge_label` (`app.rs:520`) gains an `F1 → "[F1]"` entry so demo
+  mode surfaces it (ADR-0047).
+
+## 6. The two error routes (D2 / D5)
+
+- **Runtime errors:** add `last_error_hint_key: Option<String>` to `App`.
+  Set it where friendly errors are rendered (`runtime.rs:2615`,
+  `app.rs:2424`) from the error's class key; clear on the next successful
+  command. The `hint` command and empty-input F1 read it.
+- **Pre-submit diagnostics:** the F1 live-input path, when the input
+  carries an under-cursor diagnostic, reads it straight from the walker
+  (`input_diagnostics_in_mode`, the same source the ambient panel uses)
+  and renders that diagnostic's `hint.err.<class>` block instead of (or
+  alongside) the command block. No stored state.
+- Both render from `hint.err.*`.
+
+## 7. Rendering: the `note_hint*` family (D4)
+
+- New `App::note_hint_for_input`, `note_hint_for_error`,
+  `note_getting_started` (siblings of `note_help`/`note_help_topic`,
+  `app.rs:2982`/`3021`).
+- A tier-3 block is **structured** (`what` / `example` / `concept`, plus
+  the live `Next:` line on the input path). The catalogue stores each part
+  under sub-keys (`hint.cmd.<id>.what`, `.example`, `.concept`); the
+  renderer fetches each via `t!` and lays them out as a small framed
+  block.
+- Styling: `OutputKind::System`; `OutputStyleClass::Hint` (muted) on
+  `what`/`concept`/`Next`, `Neutral` on `example` so the runnable line
+  stands out. Reuse `OutputLine::styled` + `push_category_three_prose`
+  patterns (`app.rs:3121`).
+- **Fallback:** if a node's `hint_id` is `None` or a key is missing,
+  degrade to tier-2 (ambient prose for the input path; the verbose error
+  `hint:` for the error path) — never blank.
+
+## 8. Catalogue + `keys.rs`
+
+- New sub-namespaces under the existing top-level `hint:` in
+  `src/friendly/strings/en-US.yaml`: `hint.cmd.<hint_id>.{what,example,
+  concept}` and `hint.err.<class>.{what,example,concept}`.
+- Register every key + its placeholders in `src/friendly/keys.rs`
+  (`KEYS_AND_PLACEHOLDERS`) so the build-time validation covers them.
+- `parse.usage.hint` + `help.app.hint` strings for the command itself.
+
+## 9. Content (Phase C — the bulk, batched per D7)
+
+Exemplars approved in the ADR (`insert` live-input, FK child-side error,
+`add relationship`) are the template. Author in reviewable batches:
+1. **App commands** (~16): save/save as/load/new/rebuild/export/import/
+   replay/undo/redo/mode/messages/copy/help/hint/quit.
+2. **DDL** (simple): create table, create m:n, add column/relationship/
+   index, drop, rename, change column.
+3. **DML** (simple): insert, update, delete, show, seed, explain,
+   select/with.
+4. **Advanced-mode SQL forms** (7): SQL CREATE TABLE, ALTER TABLE,
+   CREATE/DROP INDEX, DROP TABLE, SQL INSERT/UPDATE/DELETE, EXPLAIN SQL —
+   **own blocks, SQL-syntax examples**.
+5. **Runtime error classes** (9): unique, foreign_key ×{child,parent},
+   not_null, check, type_mismatch, not_found, already_exists, generic,
+   invalid_value.
+6. **`diagnostic.*` classes** (~33): arity/type/unknown-table-column/etc.
+
+Each block: `what` (1–2 sentences), `example` (one runnable line,
+mode-correct), `concept` (the relational idea — the teaching part;
+optional only where genuinely none, e.g. `quit`).
+
+## 10. Tests
+
+Written test-first against the Phase-A skeleton where possible.
+
+- **Tier 1 (unit, `app.rs`):**
+  - trigger matrix: F1 non-empty → command block; F1 empty + recent error
+    → error block; F1 empty + none → getting-started; `hint` command +
+    error → error block; `hint` + none → getting-started.
+  - `last_error_hint_key` set on a failing command, cleared on the next
+    success.
+  - routing: a pre-submit diagnostic on the input drives the diagnostic
+    `hint.err`; a runtime error drives the stored-key route.
+  - `:`-strip: `: SELECT …` in Simple mode resolves to the advanced node.
+  - **read-only overlay:** F1 leaves `input`, `input_cursor`, and
+    `last_completion` unchanged.
+  - tier-2 fallback when `hint_id`/key absent.
+- **Tier 2 (`insta`):** snapshot a representative rendered tier-3 block
+  (the `insert` exemplar) so the framed layout + styling spans are locked.
+- **Tier 3 (integration, `tests/it/`):** type a partial command → F1 →
+  block appears, buffer untouched; run a failing insert → `hint` → FK
+  error expansion.
+- **Comprehensiveness coverage test** (enforces D6, the key one): iterate
+  `REGISTRY` and assert every node has a `hint_id` resolving to a
+  `hint.cmd.*` block; assert every runtime-error + `diagnostic.*` class
+  has a `hint.err.*` block. **Red until Phase C completes** — enable
+  (un-`ignore`) as the final gate.
+- `keys.rs` validation continues to guarantee every *referenced* key
+  resolves.
+
+## 11. Keybinding strip + discoverability (Phase D)
+
+- The ADR-0051 bottom strip advertises **F1 = hint** in the editing/
+  typing state (and on the empty-input state, since F1 still does
+  something there). Re-accept the affected full-panel snapshots.
+
+## 12. ADR / docs
+
+- ADR-0053 is committed (`e16ad50`). On completion, flip its Status from
+  "implementation pending" to implemented (with date), and update the
+  README index entry + `requirements.md` **H2 → [x]** and **A1 → [x]**
+  (A1 closes when `hint` lands).
+
+## 13. Risks / watch-list
+
+- **Command-identification reuse.** The lookup exists
+  (`command_for_entry_word` + the mode-aware `usage_keys_for_input_in_mode`,
+  `grammar/mod.rs:811`/`564`); the only new code is a thin node/`hint_id`
+  variant that reuses their selection. Do **not** re-implement entry-word
+  matching — mirror the existing functions.
+- **Structured-key ergonomics.** Three sub-keys per block × ~80 blocks is
+  ~240 catalogue keys; keep the `keys.rs` registration generation tidy
+  (consider a helper that registers the `{what,example,concept}` triple
+  for an id).
+- **Content voice drift across batches.** Re-check each batch against the
+  approved exemplars; the `concept` line is where drift (too terse / too
+  advanced) creeps in. Pedagogy wins ties.
+- **F1 terminal capture.** A few terminals intercept F1; acceptable
+  (it's the convention) but note it if testing surfaces it.
+- **Snapshot churn.** The strip change re-accepts ADR-0051 snapshots;
+  keep that diff isolated.
+- **Coverage-test timing.** It is red through Phases A–C; gate it so CI
+  isn't broken mid-stream (e.g. `#[ignore]` until the final batch), then
+  make passing it the completion criterion.
+```
@@ -0,0 +1,82 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1780902259,
+        "narHash": "sha256-q8yYEC5f1mFlQO9RGna4LTc9QrcvWunX6FYp83munkQ=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "bd0ff2d3eac24699c3664d5966b9ef36f388e2ca",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-26.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay"
+      }
+    },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1781234414,
+        "narHash": "sha256-HdA+P4fKRGOomkewnI/Tww5Wz4xK1O7+hDO90YAsPB4=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "1d18bfe3de6244c641ca4e8011186d0981b81d76",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
@@ -0,0 +1,98 @@
+{
+  description = "RDBMS Playground — Rust TUI dev environment + reproducible build";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, rust-overlay, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ (import rust-overlay) ];
+        };
+
+        # Single source of the Rust toolchain: the rustup toolchain file.
+        # rust-overlay provisions the exact channel + components declared there,
+        # so the dev shell and the build package share one pinned toolchain.
+        rust = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+
+        # Read the package version straight from Cargo.toml so it never drifts
+        # from the crate metadata (no hand-maintained duplicate here).
+        cargoToml = builtins.fromTOML (builtins.readFile ./Cargo.toml);
+
+        # System build inputs are deliberately tiny — this is a pure-Rust TUI:
+        #   * libsqlite3-sys is built with the `bundled` feature, so SQLite is
+        #     compiled from vendored C. That needs a C compiler, which the
+        #     stdenv provides automatically (no entry required here).
+        #   * arboard's clipboard backend is `x11rb` — a pure-Rust socket XCB
+        #     client. It links no C X11 libraries, so none appear below. A live
+        #     X server is only needed at *runtime* to copy; headless sessions
+        #     fall back to OSC 52.
+        # If a future dependency introduces a pkg-config / native-lib link, add
+        # it here (and document why) rather than leaking it into the host env.
+        nativeBuildInputs = [ ];
+        buildInputs = [ ];
+
+        # `nix build` → the release binary, built reproducibly from the pinned
+        # toolchain and the committed Cargo.lock (importCargoLock fetches each
+        # dependency by its lockfile checksum — offline, no cargoHash to churn).
+        # CI's release job consumes this artifact; the gate's tests run
+        # separately via `nix develop -c cargo test` (see below), so the package
+        # build skips the suite — the nix sandbox has no HOME/X server and would
+        # fight the project-dirs / clipboard paths the tests touch.
+        rdbms-playground = pkgs.rustPlatform.buildRustPackage {
+          pname = cargoToml.package.name;
+          version = cargoToml.package.version;
+          src = ./.;
+          cargoLock.lockFile = ./Cargo.lock;
+          inherit nativeBuildInputs buildInputs;
+          doCheck = false;
+        };
+      in {
+        packages.default = rdbms-playground;
+        packages.rdbms-playground = rdbms-playground;
+
+        devShells.default = pkgs.mkShell {
+          buildInputs = buildInputs ++ pkgs.lib.optionals pkgs.stdenv.isDarwin [
+            # macOS release builds (aarch64/x86_64-apple-darwin) link AppKit
+            # (arboard) + libSystem; the Apple SDK provides those framework/
+            # system-lib stubs as *system* paths (/usr/lib, /System/Library).
+            # NOTE: the darwin stdenv still propagates a *nix-store* libiconv and
+            # links it regardless of inputs, so the release workflow rewrites that
+            # one load path to /usr/lib/libiconv.2.dylib (install_name_tool) and
+            # re-signs — see release-macos / the macOS smoke-test. Adding
+            # `pkgs.libiconv` here would only reinforce the wrong path, so don't.
+            pkgs.apple-sdk
+          ];
+          nativeBuildInputs = nativeBuildInputs ++ [
+            rust
+            # Dev-disk maintenance: cargo never garbage-collects stale per-hash
+            # build artifacts, so target/ creeps into the tens of GB (see
+            # CLAUDE.md "Build hygiene"). cargo-sweep prunes them; run it
+            # periodically between milestones.
+            pkgs.cargo-sweep
+          ] ++ pkgs.lib.optionals pkgs.stdenv.isLinux [
+            # Cross-compilation for the non-macOS D1 targets: `cargo zigbuild`
+            # uses Zig's bundled clang + libc as one universal cross cc/linker
+            # (incl. the `cc`-crate compile of rusqlite's bundled SQLite C) for
+            # Linux musl + Windows gnu/gnullvm. macOS builds natively with the
+            # Apple toolchain on the Mac runner, so these are Linux-only.
+            pkgs.cargo-zigbuild
+            pkgs.zig
+          ];
+
+          shellHook = ''
+            echo "RDBMS Playground dev shell ($(uname -s))"
+            echo "  rust:   $(rustc --version | cut -d' ' -f1-2)"
+            echo "  cargo:  $(cargo --version | cut -d' ' -f1-2)"
+          '';
+        };
+      });
+}
@@ -0,0 +1,26 @@
+[toolchain]
+# Pinned to an exact stable release (not the floating "stable" channel) so
+# `nix flake update` cannot surprise-bump Rust into new clippy lints that would
+# fail the `-D warnings` CI gate. Matches the host toolchain and the datamage
+# flake's convention (its ADR 0046). Bump deliberately, in its own commit.
+channel = "1.95.0"
+# rustfmt + clippy back the `fmt`/`clippy` CI stages; no coverage or WASM
+# tooling is needed here (pure-Rust TUI).
+components = ["rustfmt", "clippy"]
+# The non-macOS D1 release matrix, all cross-built from Linux x86_64 via
+# `cargo zigbuild` (D1: cross-platform binaries; D2: single static binary).
+# Linux uses musl + crt-static for fully static, portable binaries; Windows
+# uses the gnu/gnullvm ABIs (Zig statically links libc, so the .exe is
+# standalone). macOS is deferred — its arboard/AppKit link needs Apple's SDK,
+# which a Linux runner can't supply cleanly (see docs/ci/adr ADR-ci-001).
+targets = [
+  "x86_64-unknown-linux-musl",
+  "aarch64-unknown-linux-musl",
+  "x86_64-pc-windows-gnu",
+  "aarch64-pc-windows-gnullvm",
+  # macOS — built natively on the Apple-Silicon Mac runner (aarch64 native,
+  # x86_64 cross). These need Apple's SDK to link, which a Linux runner can't
+  # supply, so they are produced only on the Mac (see docs/ci/adr ADR-ci-003).
+  "aarch64-apple-darwin",
+  "x86_64-apple-darwin",
+]
@@ -271,6 +271,13 @@ pub struct App {
    pub nav_focus: NavFocus,
    pub output: VecDeque<OutputLine>,
    pub hint: Option<String>,
+    /// Catalog class key of the most recent runtime error (H2 /
+    /// ADR-0053 D5), e.g. `foreign_key.child_side`. Set when a
+    /// friendly error is rendered, cleared on the next successful
+    /// command. The submitted `hint` command and empty-input F1 use
+    /// it to render that error's tier-3 `hint.err.<class>` block.
+    /// `None` → no recent error → the "getting started" pointer.
+    pub last_error_hint_key: Option<String>,
    /// The validity indicator's currently-visible verdict
    /// (ADR-0027). `None` means the indicator shows nothing —
    /// the input is clean, or it is hidden mid-typing while the
@@ -521,6 +528,7 @@ pub const fn demo_badge_label(key: &KeyEvent) -> Option<&'static str> {
    match (key.code, key.modifiers) {
        (KeyCode::Tab, _) => Some("[TAB]"),
        (KeyCode::BackTab, _) => Some("[SHIFT-TAB]"),
+        (KeyCode::F(1), _) => Some("[F1]"),
        (KeyCode::Enter, _) => Some("[ENTER]"),
        (KeyCode::Esc, _) => Some("[ESC]"),
        (KeyCode::Up, _) => Some("[UP]"),
@@ -557,6 +565,7 @@ impl App {
            nav_focus: NavFocus::Input,
            output: VecDeque::with_capacity(OUTPUT_CAPACITY),
            hint: None,
+            last_error_hint_key: None,
            input_indicator: None,
            tables: Vec::new(),
            relationships: Vec::new(),
@@ -1208,6 +1217,21 @@ impl App {
            return self.handle_nav_key(key);
        }

+        // H2 / ADR-0053: F1 is a read-only contextual-hint overlay —
+        // it emits into the output journal and must NOT touch the input
+        // buffer, cursor, or the completion memo, so it sits ahead of
+        // the memo-clearing completion match below. Non-empty input →
+        // a hint for the command being typed; empty input → expand on
+        // the most recent error (or a getting-started pointer).
+        if key.code == KeyCode::F(1) {
+            if self.input.trim().is_empty() {
+                self.note_hint_for_recent_error();
+            } else {
+                self.note_hint_for_input();
+            }
+            return Vec::new();
+        }
+
        // ADR-0022 stage 8 — non-modal completion. Tab /
        // Shift-Tab cycle; Esc / Backspace undo the whole
        // last-Tab insertion in one keystroke while the memo
@@ -1774,6 +1798,13 @@ impl App {
        // recallable. The canonical (un-prefixed) text is what reaches
        // the journal via `ExecuteDsl.source`.
        let is_app = matches!(&parsed, Ok(Command::App(_)));
+        // H2 / ADR-0053 D5: a new *DSL* command supersedes the previous
+        // runtime error for `hint`. App commands (incl. `hint` itself)
+        // and parse errors leave it intact, so `hint` still expands the
+        // last real error after, say, a `help` in between.
+        if matches!(&parsed, Ok(cmd) if !matches!(cmd, Command::App(_))) {
+            self.last_error_hint_key = None;
+        }
        let advanced = submission_mode.is_advanced() && !is_app;
        let ring_line = if advanced {
            format!(": {effective_input}")
@@ -1814,6 +1845,13 @@ impl App {
                }
                Vec::new()
            }
+            // H2 / ADR-0053: a submitted `hint` acts on the most recent
+            // runtime error (the buffer is empty post-submit). The
+            // live-input surface is the F1 keybinding (handle_key).
+            AppCommand::Hint => {
+                self.note_hint_for_recent_error();
+                Vec::new()
+            }
            AppCommand::Rebuild => vec![Action::PrepareRebuild],
            AppCommand::Save => self.handle_save_command(false),
            AppCommand::SaveAs => self.handle_save_command(true),
@@ -2422,6 +2460,10 @@ impl App {
        // runtime built before posting the event.
        let ctx = self.build_translate_context(command, facts);
        let rendered = crate::friendly::translate_error(&error, &ctx).render();
+        // H2 / ADR-0053 D5: remember this error's tier-3 class so a
+        // following `hint` (or empty-input F1) can expand on it.
+        self.last_error_hint_key =
+            crate::friendly::error_hint_class(&error, &ctx).map(String::from);
        warn!(
            verb = command.verb(),
            error = %rendered,
@@ -3091,6 +3133,94 @@ impl App {
        }
    }

+    // ── H2 / ADR-0053: contextual `hint` ────────────────────────
+    // Phase A wires the two surfaces (F1 → live input; the `hint`
+    // command → most recent error) plus the tier-2 fallback. The
+    // tier-3 corpus (`hint.cmd.*` / `hint.err.*`) is authored in later
+    // phases; until a block exists, `emit_tier3_block` returns false
+    // and the surface degrades to the ambient prose / getting-started
+    // pointer — never blank.
+
+    /// F1 with a non-empty buffer: a tier-3 hint for the command form
+    /// being typed, else the tier-2 ambient prose (ADR-0053 D2).
+    /// Read-only — callers guarantee the buffer/cursor/memo are left
+    /// untouched.
+    fn note_hint_for_input(&mut self) {
+        // `feedback_view` strips the `:` one-shot sigil and
+        // `effective_mode` reflects the one-shot advanced surface, so
+        // the hint matches the command the user is actually typing.
+        let (view, cursor, _off) = self.feedback_view();
+        let probe = view.to_string();
+        let mode = self.effective_mode().as_mode();
+        if let Some(id) = crate::dsl::grammar::hint_key_for_input_in_mode(&probe, mode)
+            && self.emit_tier3_block(&format!("hint.cmd.{id}"))
+        {
+            return;
+        }
+        // Tier-2 fallback: surface the ambient prose as a persistent
+        // line (computed exactly as the live panel does).
+        let ambient = crate::input_render::ambient_hint_in_mode(
+            &probe,
+            cursor,
+            self.last_completion.as_ref(),
+            &self.schema_cache,
+            mode,
+        );
+        match ambient {
+            Some(crate::input_render::AmbientHint::Prose(text)) => {
+                self.push_category_three_prose(text);
+            }
+            Some(crate::input_render::AmbientHint::Candidates { items, .. }) => {
+                let names = items
+                    .iter()
+                    .map(|c| c.text.clone())
+                    .collect::<Vec<_>>()
+                    .join(", ");
+                self.push_category_three_prose(crate::t!("hint.ambient_expected", expected = names));
+            }
+            None => self.note_getting_started(),
+        }
+    }
+
+    /// The `hint` command (and empty-input F1): expand on the most
+    /// recent runtime error, else point the user at how to start
+    /// (ADR-0053 D2/D5).
+    fn note_hint_for_recent_error(&mut self) {
+        if let Some(class) = self.last_error_hint_key.clone()
+            && self.emit_tier3_block(&format!("hint.err.{class}"))
+        {
+            return;
+        }
+        self.note_getting_started();
+    }
+
+    fn note_getting_started(&mut self) {
+        self.note_system(crate::t!("hint.getting_started"));
+    }
+
+    /// Render a tier-3 block (`<stem>.what` / `.example` / `.concept`)
+    /// when it has been authored; returns `false` if the `what` part is
+    /// absent so the caller can fall back to tier 2. `what` is
+    /// mandatory, `example`/`concept` optional (ADR-0053 D3). Styling
+    /// polish (the framed block) lands with the corpus.
+    fn emit_tier3_block(&mut self, stem: &str) -> bool {
+        let cat = crate::friendly::catalog();
+        if cat.get(&format!("{stem}.what")).is_none() {
+            return false;
+        }
+        self.note_system(crate::friendly::translate(&format!("{stem}.what"), &[]));
+        if cat.get(&format!("{stem}.example")).is_some() {
+            self.note_system(crate::friendly::translate(&format!("{stem}.example"), &[]));
+        }
+        if cat.get(&format!("{stem}.concept")).is_some() {
+            self.push_category_three_prose(crate::friendly::translate(
+                &format!("{stem}.concept"),
+                &[],
+            ));
+        }
+        true
+    }
+
    fn note_system(&mut self, text: impl Into<String>) {
        self.push_multiline(text.into(), OutputKind::System);
    }
@@ -5539,6 +5669,219 @@ mod tests {
        assert!(last.text.contains("Ghost"), "{}", last.text);
    }

+    // ── H2 / ADR-0053: contextual `hint` (Phase A skeleton) ──────
+
+    fn f1(app: &mut App) -> Vec<Action> {
+        app.update(key(KeyCode::F(1)))
+    }
+
+    fn no_such_table_failure() -> AppEvent {
+        AppEvent::DslFailed {
+            command: Command::DropTable {
+                name: "Ghost".to_string(),
+            },
+            error: crate::db::DbError::Sqlite {
+                message: "no such table: Ghost".to_string(),
+                kind: crate::db::SqliteErrorKind::NoSuchTable,
+            },
+            facts: crate::friendly::FailureContext::default(),
+            source: String::new(),
+            advanced: false,
+        }
+    }
+
+    #[test]
+    fn hint_command_parses_to_app_hint() {
+        use crate::dsl::{parse_command, AppCommand, Command};
+        assert!(matches!(
+            parse_command("hint"),
+            Ok(Command::App(AppCommand::Hint))
+        ));
+    }
+
+    #[test]
+    fn hint_command_with_no_recent_error_shows_getting_started() {
+        let mut app = App::new();
+        type_str(&mut app, "hint");
+        submit(&mut app);
+        assert!(output_contains(&app, "press F1"), "{}", error_lines(&app));
+    }
+
+    #[test]
+    fn f1_on_empty_input_with_no_error_shows_getting_started() {
+        let mut app = App::new();
+        let before = app.output.len();
+        f1(&mut app);
+        assert!(app.output.len() > before, "F1 must emit something");
+        assert!(output_contains(&app, "press F1"));
+    }
+
+    #[test]
+    fn f1_is_a_read_only_overlay() {
+        let mut app = App::new();
+        type_str(&mut app, "insert into T");
+        let input = app.input.clone();
+        let cursor = app.input_cursor;
+        let before = app.output.len();
+        f1(&mut app);
+        assert_eq!(app.input, input, "F1 must not change the buffer");
+        assert_eq!(app.input_cursor, cursor, "F1 must not move the cursor");
+        assert!(app.output.len() > before, "F1 emits a hint line");
+    }
+
+    #[test]
+    fn f1_preserves_the_completion_memo() {
+        let mut app = App::new();
+        type_str(&mut app, "show ");
+        app.update(key(KeyCode::Tab));
+        assert!(app.last_completion.is_some(), "precondition: Tab sets the memo");
+        let input = app.input.clone();
+        f1(&mut app);
+        assert!(app.last_completion.is_some(), "F1 must not clear the memo");
+        assert_eq!(app.input, input, "F1 must not change the buffer");
+    }
+
+    #[test]
+    fn dsl_failure_sets_hint_class_and_a_later_dsl_command_clears_it() {
+        let mut app = App::new();
+        app.update(no_such_table_failure());
+        assert_eq!(app.last_error_hint_key.as_deref(), Some("not_found"));
+        // A new DSL command supersedes the previous error.
+        type_str(&mut app, "drop table Ghost");
+        submit(&mut app);
+        assert_eq!(app.last_error_hint_key, None);
+    }
+
+    #[test]
+    fn app_command_does_not_clear_the_hint_class() {
+        let mut app = App::new();
+        app.update(no_such_table_failure());
+        assert_eq!(app.last_error_hint_key.as_deref(), Some("not_found"));
+        // `help` (an app command) leaves the last error intact, so a
+        // following `hint` still expands on it.
+        type_str(&mut app, "help");
+        submit(&mut app);
+        assert_eq!(
+            app.last_error_hint_key.as_deref(),
+            Some("not_found"),
+            "an app command must not clear the last error's hint class"
+        );
+    }
+
+    #[test]
+    fn hint_after_error_emits_a_hint_without_panicking() {
+        // Phase A: no tier-3 `hint.err.*` content exists yet, so the
+        // error path falls back to the getting-started pointer. (Phase C
+        // replaces this with the real error block.)
+        let mut app = App::new();
+        app.update(no_such_table_failure());
+        let before = app.output.len();
+        type_str(&mut app, "hint");
+        submit(&mut app);
+        assert!(app.output.len() > before, "hint must emit something");
+    }
+
+    #[test]
+    fn help_list_includes_hint() {
+        let mut app = App::new();
+        type_str(&mut app, "help");
+        submit(&mut app);
+        assert!(
+            output_contains(&app, "explain the most recent error"),
+            "help list must advertise the hint command"
+        );
+    }
+
+    #[test]
+    fn help_hint_describes_the_hint_command() {
+        let mut app = App::new();
+        type_str(&mut app, "help hint");
+        submit(&mut app);
+        assert!(output_contains(&app, "explain the most recent error"));
+    }
+
+    // ── Phase B: tier-3 exemplar content renders ────────────────
+
+    #[test]
+    fn f1_on_insert_input_renders_the_insert_hint_block() {
+        let mut app = App::new();
+        type_str(&mut app, "insert into Customers ");
+        f1(&mut app);
+        assert!(
+            output_contains(&app, "Add one or more rows to a table"),
+            "expected the insert tier-3 block"
+        );
+    }
+
+    #[test]
+    fn f1_on_add_relationship_renders_the_relationship_block() {
+        let mut app = App::new();
+        type_str(&mut app, "add 1:n relationship from Customers.id to Orders.cust ");
+        f1(&mut app);
+        assert!(
+            output_contains(&app, "one parent, many children"),
+            "expected the add-relationship tier-3 block"
+        );
+    }
+
+    #[test]
+    fn f1_on_add_column_does_not_render_the_relationship_block() {
+        // Per-form disambiguation (ADR-0053 D3): `add column` resolves
+        // to `add_column` (no tier-3 block yet → tier-2 fallback), NOT
+        // the relationship block — proving the multi-form node keys
+        // per form, not per node.
+        let mut app = App::new();
+        type_str(&mut app, "add column Note text to Customers");
+        f1(&mut app);
+        assert!(!output_contains(&app, "one parent, many children"));
+        assert!(!output_contains(&app, "1:n"));
+    }
+
+    #[test]
+    fn hint_renders_the_foreign_key_error_block() {
+        let mut app = App::new();
+        app.last_error_hint_key = Some("foreign_key.child_side".to_string());
+        type_str(&mut app, "hint");
+        submit(&mut app);
+        assert!(
+            output_contains(&app, "doesn't match any parent row"),
+            "expected the FK child-side tier-3 block"
+        );
+    }
+
+    // ── Phase C batch 1: app-command hints render ───────────────
+
+    #[test]
+    fn f1_on_an_app_command_renders_its_hint_block() {
+        let mut app = App::new();
+        type_str(&mut app, "mode advanced");
+        f1(&mut app);
+        assert!(
+            output_contains(&app, "Switch between simple mode"),
+            "expected the `mode` tier-3 block"
+        );
+    }
+
+    // ── Phase C batch 2: DDL hints render (incl. multi-form DROP) ──
+
+    #[test]
+    fn f1_on_create_table_renders_its_hint_block() {
+        let mut app = App::new();
+        type_str(&mut app, "create table Customers with pk id(serial)");
+        f1(&mut app);
+        assert!(output_contains(&app, "Create a new table"));
+    }
+
+    #[test]
+    fn f1_disambiguates_drop_forms() {
+        let mut app = App::new();
+        type_str(&mut app, "drop index idx_email");
+        f1(&mut app);
+        // Resolves drop_index, not drop_table/column/etc.
+        assert!(output_contains(&app, "Remove an index by name"));
+        assert!(!output_contains(&app, "Remove a table"));
+    }
+
    #[test]
    fn messages_command_toggles_verbosity_and_reports() {
        let mut app = App::new();
@@ -552,6 +552,11 @@ pub enum AppCommand {
    Help {
        topic: Option<String>,
    },
+    /// Show a contextual tier-3 hint (H2 / ADR-0053). No argument:
+    /// when submitted, it expands on the most recent runtime error
+    /// (the buffer is empty post-submit). The live-input surface is
+    /// the F1 keybinding, handled in `App::handle_key`, not here.
+    Hint,
    /// Rebuild `playground.db` from `project.yaml` + data/, with
    /// confirmation modal.
    Rebuild,
@@ -1013,6 +1018,7 @@ impl Command {
            Self::App(app) => match app {
                AppCommand::Quit => "quit",
                AppCommand::Help { .. } => "help",
+                AppCommand::Hint => "hint",
                AppCommand::Rebuild => "rebuild",
                AppCommand::Save => "save",
                AppCommand::SaveAs => "save as",
@@ -177,6 +177,9 @@ const fn build_rebuild(_path: &MatchedPath, _source: &str) -> Result<Command, Va
 const fn build_undo(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
    Ok(Command::App(AppCommand::Undo))
 }
+const fn build_hint(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
+    Ok(Command::App(AppCommand::Hint))
+}

 const fn build_redo(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
    Ok(Command::App(AppCommand::Redo))
@@ -263,6 +266,7 @@ pub static QUIT: CommandNode = CommandNode {
    shape: EMPTY_SEQ,
    ast_builder: build_quit,
    help_id: Some("app.quit"),
+    hint_ids: &["quit"],
    usage_ids: &["parse.usage.quit"],};

 pub static HELP: CommandNode = CommandNode {
@@ -270,13 +274,24 @@ pub static HELP: CommandNode = CommandNode {
    shape: HELP_TOPIC_OPT,
    ast_builder: build_help,
    help_id: Some("app.help"),
+    hint_ids: &["help"],
    usage_ids: &["parse.usage.help"],};

+pub static HINT: CommandNode = CommandNode {
+    entry: Word::keyword("hint"),
+    shape: EMPTY_SEQ,
+    ast_builder: build_hint,
+    help_id: Some("app.hint"),
+    // hint_id assigned in Phase C with the tier-3 corpus (ADR-0053).
+    hint_ids: &["hint"],
+    usage_ids: &["parse.usage.hint"],};
+
 pub static REBUILD: CommandNode = CommandNode {
    entry: Word::keyword("rebuild"),
    shape: EMPTY_SEQ,
    ast_builder: build_rebuild,
    help_id: Some("app.rebuild"),
+    hint_ids: &["rebuild"],
    usage_ids: &["parse.usage.rebuild"],};

 pub static SAVE: CommandNode = CommandNode {
@@ -284,6 +299,7 @@ pub static SAVE: CommandNode = CommandNode {
    shape: SAVE_AS_OPT,
    ast_builder: build_save,
    help_id: Some("app.save"),
+    hint_ids: &["save"],
    usage_ids: &["parse.usage.save"],};

 pub static NEW: CommandNode = CommandNode {
@@ -291,6 +307,7 @@ pub static NEW: CommandNode = CommandNode {
    shape: EMPTY_SEQ,
    ast_builder: build_new,
    help_id: Some("app.new"),
+    hint_ids: &["new"],
    usage_ids: &["parse.usage.new"],};

 pub static LOAD: CommandNode = CommandNode {
@@ -298,6 +315,7 @@ pub static LOAD: CommandNode = CommandNode {
    shape: EMPTY_SEQ,
    ast_builder: build_load,
    help_id: Some("app.load"),
+    hint_ids: &["load"],
    usage_ids: &["parse.usage.load"],};

 pub static EXPORT: CommandNode = CommandNode {
@@ -305,6 +323,7 @@ pub static EXPORT: CommandNode = CommandNode {
    shape: EXPORT_PATH_OPT,
    ast_builder: build_export,
    help_id: Some("app.export"),
+    hint_ids: &["export"],
    usage_ids: &["parse.usage.export"],};

 pub static IMPORT: CommandNode = CommandNode {
@@ -312,6 +331,7 @@ pub static IMPORT: CommandNode = CommandNode {
    shape: IMPORT_BODY_OPT,
    ast_builder: build_import,
    help_id: Some("app.import"),
+    hint_ids: &["import"],
    usage_ids: &["parse.usage.import"],};

 pub static MODE: CommandNode = CommandNode {
@@ -319,6 +339,7 @@ pub static MODE: CommandNode = CommandNode {
    shape: MODE_VALUE,
    ast_builder: build_mode,
    help_id: Some("app.mode"),
+    hint_ids: &["mode"],
    usage_ids: &["parse.usage.mode"],};

 pub static MESSAGES: CommandNode = CommandNode {
@@ -326,6 +347,7 @@ pub static MESSAGES: CommandNode = CommandNode {
    shape: MESSAGES_VALUE_OPT,
    ast_builder: build_messages,
    help_id: Some("app.messages"),
+    hint_ids: &["messages"],
    usage_ids: &["parse.usage.messages"],};

 pub static UNDO: CommandNode = CommandNode {
@@ -333,6 +355,7 @@ pub static UNDO: CommandNode = CommandNode {
    shape: EMPTY_SEQ,
    ast_builder: build_undo,
    help_id: Some("app.undo"),
+    hint_ids: &["undo"],
    usage_ids: &["parse.usage.undo"],};

 pub static REDO: CommandNode = CommandNode {
@@ -340,6 +363,7 @@ pub static REDO: CommandNode = CommandNode {
    shape: EMPTY_SEQ,
    ast_builder: build_redo,
    help_id: Some("app.redo"),
+    hint_ids: &["redo"],
    usage_ids: &["parse.usage.redo"],};

 pub static COPY: CommandNode = CommandNode {
@@ -347,4 +371,5 @@ pub static COPY: CommandNode = CommandNode {
    shape: COPY_VALUE_OPT,
    ast_builder: build_copy,
    help_id: Some("app.copy"),
+    hint_ids: &["copy"],
    usage_ids: &["parse.usage.copy"],};
@@ -1790,6 +1790,7 @@ pub static SHOW: CommandNode = CommandNode {
    shape: SHOW_SHAPE,
    ast_builder: build_show,
    help_id: Some("data.show"),
+    hint_ids: &[],
    usage_ids: &[
        "parse.usage.show_data",
        "parse.usage.show_table",
@@ -1805,6 +1806,7 @@ pub static SEED: CommandNode = CommandNode {
    shape: SEED_SHAPE,
    ast_builder: build_seed,
    help_id: Some("data.seed"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.seed"],
 };

@@ -1813,6 +1815,8 @@ pub static INSERT: CommandNode = CommandNode {
    shape: INSERT_SHAPE,
    ast_builder: build_insert,
    help_id: Some("data.insert"),
+    // ADR-0053 Phase-B exemplar.
+    hint_ids: &["insert"],
    usage_ids: &["parse.usage.insert"],};

 pub static UPDATE: CommandNode = CommandNode {
@@ -1820,6 +1824,7 @@ pub static UPDATE: CommandNode = CommandNode {
    shape: UPDATE_SHAPE,
    ast_builder: build_update,
    help_id: Some("data.update"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.update"],};

 pub static DELETE: CommandNode = CommandNode {
@@ -1827,6 +1832,7 @@ pub static DELETE: CommandNode = CommandNode {
    shape: DELETE_SHAPE,
    ast_builder: build_delete,
    help_id: Some("data.delete"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.delete"],};

 pub static REPLAY: CommandNode = CommandNode {
@@ -1834,6 +1840,7 @@ pub static REPLAY: CommandNode = CommandNode {
    shape: REPLAY_PATH,
    ast_builder: build_replay,
    help_id: Some("data.replay"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.replay"],};

 pub static EXPLAIN: CommandNode = CommandNode {
@@ -1841,6 +1848,7 @@ pub static EXPLAIN: CommandNode = CommandNode {
    shape: EXPLAIN_SHAPE,
    ast_builder: build_explain,
    help_id: Some("data.explain"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.explain"],};

 /// `explain` over advanced-mode SQL (ADR-0039).
@@ -1860,6 +1868,7 @@ pub static EXPLAIN_SQL: CommandNode = CommandNode {
    // too). Mirrors the `SQL_INSERT`/`SQL_UPDATE`/`SQL_DELETE`
    // precedent; otherwise `note_help` would print `explain` twice.
    help_id: None,
+    hint_ids: &[],
    usage_ids: &[],};

 /// SQL `SELECT` (ADR-0030 §6, ADR-0031, ADR-0032).
@@ -1875,6 +1884,7 @@ pub static SELECT: CommandNode = CommandNode {
    shape: Node::Subgrammar(&sql_select::SQL_SELECT_TAIL),
    ast_builder: build_select,
    help_id: None,
+    hint_ids: &[],
    usage_ids: &["parse.usage.select"],};

 /// `WITH …` top-level statement (ADR-0032 §4 / sub-phase 2c).
@@ -1889,6 +1899,7 @@ pub static WITH: CommandNode = CommandNode {
    shape: Node::Subgrammar(&sql_select::SQL_WITH_TAIL),
    ast_builder: build_select,
    help_id: None,
+    hint_ids: &[],
    usage_ids: &["parse.usage.with"],};

 /// SQL `INSERT` — the `Advanced`-category node of the shared
@@ -1906,6 +1917,7 @@ pub static SQL_INSERT: CommandNode = CommandNode {
    shape: Node::Subgrammar(&sql_insert::SQL_INSERT_SHAPE),
    ast_builder: build_sql_insert,
    help_id: None,
+    hint_ids: &[],
    usage_ids: &[],
 };

@@ -1919,6 +1931,7 @@ pub static SQL_UPDATE: CommandNode = CommandNode {
    shape: Node::Subgrammar(&sql_update::SQL_UPDATE_SHAPE),
    ast_builder: build_sql_update,
    help_id: None,
+    hint_ids: &[],
    usage_ids: &[],
 };

@@ -1934,6 +1947,7 @@ pub static SQL_DELETE: CommandNode = CommandNode {
    shape: Node::Subgrammar(&sql_delete::SQL_DELETE_SHAPE),
    ast_builder: build_sql_delete,
    help_id: None,
+    hint_ids: &[],
    usage_ids: &[],
 };

@@ -968,6 +968,13 @@ pub static DROP: CommandNode = CommandNode {
    shape: DROP_SHAPE,
    ast_builder: build_drop,
    help_id: Some("ddl.drop"),
+    hint_ids: &[
+        "drop_table",
+        "drop_column",
+        "drop_relationship",
+        "drop_index",
+        "drop_constraint",
+    ],
    usage_ids: &[
        "parse.usage.drop_table",
        "parse.usage.drop_column",
@@ -981,6 +988,16 @@ pub static ADD: CommandNode = CommandNode {
    shape: ADD_SHAPE,
    ast_builder: build_add,
    help_id: Some("ddl.add"),
+    // Per-form (ADR-0053 D3): every form is listed so the form-word
+    // disambiguation resolves correctly; forms without an authored
+    // block yet fall back to tier-2 at render. `add_relationship` is
+    // authored as a Phase-B exemplar.
+    hint_ids: &[
+        "add_column",
+        "add_relationship",
+        "add_index",
+        "add_constraint",
+    ],
    usage_ids: &[
        "parse.usage.add_column",
        "parse.usage.add_relationship",
@@ -993,6 +1010,7 @@ pub static RENAME: CommandNode = CommandNode {
    shape: RENAME_COLUMN,
    ast_builder: build_rename_column,
    help_id: Some("ddl.rename"),
+    hint_ids: &["rename_column"],
    usage_ids: &["parse.usage.rename_column"],};

 pub static CHANGE: CommandNode = CommandNode {
@@ -1000,6 +1018,7 @@ pub static CHANGE: CommandNode = CommandNode {
    shape: CHANGE_COLUMN,
    ast_builder: build_change_column,
    help_id: Some("ddl.change"),
+    hint_ids: &["change_column"],
    usage_ids: &["parse.usage.change_column"],};

 // =================================================================
@@ -1360,6 +1379,7 @@ pub static CREATE: CommandNode = CommandNode {
    shape: CREATE_TABLE,
    ast_builder: build_create_table,
    help_id: Some("ddl.create"),
+    hint_ids: &["create_table"],
    usage_ids: &["parse.usage.create_table"],};

 // =================================================================
@@ -1428,6 +1448,7 @@ pub static CREATE_M2N: CommandNode = CommandNode {
    shape: CREATE_M2N_SHAPE,
    ast_builder: build_create_m2n,
    help_id: Some("ddl.create_m2n"),
+    hint_ids: &["create_m2n"],
    usage_ids: &["parse.usage.create_m2n"],
 };

@@ -1858,6 +1879,7 @@ pub static SQL_CREATE_TABLE: CommandNode = CommandNode {
    shape: Node::Subgrammar(&super::sql_create_table::SQL_CREATE_TABLE_SHAPE),
    ast_builder: build_sql_create_table,
    help_id: Some("ddl.sql_create_table"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.sql_create_table"],
 };

@@ -1877,6 +1899,7 @@ pub static SQL_DROP_TABLE: CommandNode = CommandNode {
    shape: SQL_DROP_TABLE_SHAPE,
    ast_builder: build_sql_drop_table,
    help_id: Some("ddl.sql_drop_table"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.sql_drop_table"],
 };

@@ -1896,6 +1919,7 @@ pub static SQL_DROP_INDEX: CommandNode = CommandNode {
    shape: SQL_DROP_INDEX_SHAPE,
    ast_builder: build_sql_drop_index,
    help_id: Some("ddl.sql_drop_index"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.sql_drop_index"],
 };

@@ -1977,6 +2001,7 @@ pub static SQL_CREATE_INDEX: CommandNode = CommandNode {
    shape: SQL_CREATE_INDEX_SHAPE,
    ast_builder: build_sql_create_index,
    help_id: Some("ddl.sql_create_index"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.sql_create_index"],
 };

@@ -2535,6 +2560,7 @@ pub static SQL_ALTER_TABLE: CommandNode = CommandNode {
    shape: SQL_ALTER_TABLE_SHAPE,
    ast_builder: build_sql_alter_table,
    help_id: Some("ddl.sql_alter_table"),
+    hint_ids: &[],
    usage_ids: &["parse.usage.sql_alter_table"],
 };

@@ -530,6 +530,18 @@ pub struct CommandNode {
    /// so a newly-registered command appears in `help`
    /// automatically (ADR-0024 §help_id).
    pub help_id: Option<&'static str>,
+    /// Catalog key stems (`hint.cmd.<id>`) for this command's
+    /// **tier-3** contextual hints (ADR-0053 / H2), **one per form**,
+    /// mirroring `usage_ids`. A single-form command carries one; a
+    /// multi-form command (`add`, `drop`, `show`, `create`) carries
+    /// one per form so a live-input hint can be specific to the form
+    /// being typed (`hint.cmd.add_relationship`, not a shared `add`
+    /// block). `hint_key_for_input_in_mode` disambiguates by the form
+    /// word, reusing `usage_key_for_input_in_mode`'s logic. Empty
+    /// until a form's tier-3 block is authored (the surface falls back
+    /// to tier-2 ambient/error text). Distinct from `help_id` (which is
+    /// `None` on advanced-SQL forms purely to dedup the `help` list).
+    pub hint_ids: &'static [&'static str],
    /// Catalog keys under `parse.usage.*` to render in the
    /// "usage:" block when a parse error fires for this command
    /// (ADR-0021 §1, ADR-0024 §architecture). Multi-form families
@@ -574,32 +586,79 @@ pub fn usage_keys_for_input_in_mode(
    source: &str,
    mode: crate::mode::Mode,
 ) -> Option<(&'static str, Vec<&'static str>)> {
-    use crate::dsl::walker::lex_helpers::{consume_ident, skip_whitespace};
-    let start = skip_whitespace(source, 0);
-    let (kw_start, kw_end) = consume_ident(source, start)?;
-    let word = &source[kw_start..kw_end];
-    let candidates = commands_for_entry_word(word);
-    if candidates.is_empty() {
+    let pick = selected_nodes_for_input_in_mode(source, mode);
+    if pick.is_empty() {
        return None;
    }
-    let union = |nodes: &[(usize, &'static CommandNode, CommandCategory)]| -> Vec<&'static str> {
    let mut keys: Vec<&'static str> = Vec::new();
-        for (_, node, _) in nodes {
+    for (_, node, _) in &pick {
        for k in node.usage_ids {
            if !keys.contains(k) {
                keys.push(*k);
            }
        }
    }
-        keys
+    if keys.is_empty() {
+        return None;
+    }
+    let entry = pick[0].1.entry.primary;
+    Some((entry, keys))
+}
+
+/// The single tier-3 hint key (`hint.cmd.<id>` stem) for the command
+/// **form** `source` is currently typing, in `mode` (H2 / ADR-0053).
+///
+/// Mirrors [`usage_key_for_input_in_mode`]: the union of the
+/// mode-selected nodes' `hint_ids`, disambiguated to the typed form by
+/// [`pick_form_key`] — so `add 1:n relationship` resolves to the
+/// relationship hint, and an advanced-SQL form resolves to its own
+/// (not its simple sibling's). `None` if no entry word matches or the
+/// form has no tier-3 block yet (the caller falls back to tier-2).
+#[must_use]
+pub fn hint_key_for_input_in_mode(source: &str, mode: crate::mode::Mode) -> Option<&'static str> {
+    let nodes = selected_nodes_for_input_in_mode(source, mode);
+    if nodes.is_empty() {
+        return None;
+    }
+    let mut keys: Vec<&'static str> = Vec::new();
+    for (_, node, _) in &nodes {
+        for k in node.hint_ids {
+            if !keys.contains(k) {
+                keys.push(*k);
+            }
+        }
+    }
+    pick_form_key(source, &keys)
+}
+
+/// Shared mode-aware command-form selection for the entry word at the
+/// start of `source`.
+///
+/// Extracted so the usage-key and hint-id lookups agree on which form
+/// the user is typing.
+///
+/// Advanced mode: every candidate form is reachable — the SQL nodes
+/// are primary, and the DSL nodes remain valid via fallback (verified:
+/// `create table … with pk` and `drop column …` both run in advanced
+/// mode). Mode-primary (Advanced) first, so a hint never hides input
+/// that works. Simple mode: only the DSL forms — the SQL-only forms
+/// hit the "this is SQL" rail and are not reachable. (ADR-0042 G3.)
+/// Degenerate guard: an advanced-only word in simple mode leaves the
+/// selection empty; fall back to all candidates.
+fn selected_nodes_for_input_in_mode(
+    source: &str,
+    mode: crate::mode::Mode,
+) -> Vec<(usize, &'static CommandNode, CommandCategory)> {
+    use crate::dsl::walker::lex_helpers::{consume_ident, skip_whitespace};
+    let start = skip_whitespace(source, 0);
+    let Some((kw_start, kw_end)) = consume_ident(source, start) else {
+        return Vec::new();
    };
-    // Advanced mode: every candidate form is reachable — the SQL
-    // nodes are primary, and the DSL nodes remain valid via fallback
-    // (verified: `create table … with pk` and `drop column …` both
-    // run in advanced mode). Show them all, mode-primary (Advanced)
-    // first, so the usage hint never hides input that works. Simple
-    // mode: only the DSL forms — the SQL-only forms hit the "this is
-    // SQL" rail and are not reachable. (ADR-0042 G3.)
+    let word = &source[kw_start..kw_end];
+    let candidates = commands_for_entry_word(word);
+    if candidates.is_empty() {
+        return Vec::new();
+    }
    let selected: Vec<(usize, &'static CommandNode, CommandCategory)> =
        if mode == crate::mode::Mode::Advanced {
            let mut v: Vec<_> = candidates
@@ -621,17 +680,7 @@ pub fn usage_keys_for_input_in_mode(
                .filter(|(_, _, c)| *c == CommandCategory::Simple)
                .collect()
        };
-    // Degenerate guard: an advanced-only word in simple mode (not
-    // normally reachable — it hits the SQL rail first) leaves
-    // `selected` empty; fall back to all candidates so a usage block
-    // still renders rather than the available-commands fallback.
-    let pick = if selected.is_empty() { candidates } else { selected };
-    let keys = union(&pick);
-    if keys.is_empty() {
-        return None;
-    }
-    let entry = pick[0].1.entry.primary;
-    Some((entry, keys))
+    if selected.is_empty() { candidates } else { selected }
 }

 /// The single usage template most relevant to `source`, when
@@ -658,14 +707,24 @@ pub fn usage_key_for_input_in_mode(
    source: &str,
    mode: crate::mode::Mode,
 ) -> Option<&'static str> {
-    use crate::dsl::walker::lex_helpers::{consume_ident, skip_whitespace};
    let (_entry, keys) = usage_keys_for_input_in_mode(source, mode)?;
+    pick_form_key(source, &keys)
+}
+
+/// From the form word after the entry keyword, pick the single `keys`
+/// entry for the form `source` names.
+///
+/// A single-entry list resolves to its one key; a multi-form list
+/// disambiguates by the form word (`add 1:n relationship` → the
+/// `…relationship` key, `create m:n …` → the `…m2n` key, else the
+/// identifier form word matched against each key's suffix). Shared by
+/// the usage-template and tier-3-hint single-key lookups so they agree.
+fn pick_form_key<'a>(source: &str, keys: &[&'a str]) -> Option<&'a str> {
+    use crate::dsl::walker::lex_helpers::{consume_ident, skip_whitespace};
    let first = *keys.first()?;
    if keys.len() == 1 {
        return Some(first);
    }
-    // Multi-form: the form is named by the token right after
-    // the entry keyword.
    let start = skip_whitespace(source, 0);
    let (_, entry_end) = consume_ident(source, start)?;
    let after = skip_whitespace(source, entry_end);
@@ -674,14 +733,12 @@ pub fn usage_key_for_input_in_mode(
        return keys.iter().copied().find(|k| k.ends_with("relationship"));
    }
    // The `create m:n relationship` form (ADR-0045) opens with `m:n`
-    // — a letter, so the digit branch misses it, and its usage key ends
-    // `…create_m2n` (not `relationship`).
+    // — a letter, so the digit branch misses it; its key ends `…m2n`.
    if source[after..].get(..3).is_some_and(|s| s.eq_ignore_ascii_case("m:n")) {
        return keys.iter().copied().find(|k| k.ends_with("m2n"));
    }
-    // Otherwise the form word is an identifier — `column`,
-    // `index`, `table`, `relationship` — matched against the
-    // usage key's suffix.
+    // Otherwise the form word is an identifier — `column`, `index`,
+    // `table`, `relationship` — matched against each key's suffix.
    let (s, e) = consume_ident(source, after)?;
    let form = source[s..e].to_ascii_lowercase();
    keys.iter().copied().find(|k| k.ends_with(form.as_str()))
@@ -712,6 +769,7 @@ pub fn entry_words_alphabetised() -> Vec<&'static str> {
 pub static REGISTRY: &[(&CommandNode, CommandCategory)] = &[
    (&app::QUIT, CommandCategory::Simple),
    (&app::HELP, CommandCategory::Simple),
+    (&app::HINT, CommandCategory::Simple),
    (&app::REBUILD, CommandCategory::Simple),
    (&app::SAVE, CommandCategory::Simple),
    (&app::NEW, CommandCategory::Simple),
@@ -836,6 +894,39 @@ pub fn commands_for_entry_word(
        .collect()
 }

+#[cfg(test)]
+mod hint_key_tests {
+    use super::hint_key_for_input_in_mode;
+    use crate::mode::Mode;
+
+    /// Per-form hint keying (ADR-0053 D3): a multi-form command
+    /// resolves the *typed* form, not the node — `add 1:n
+    /// relationship` → the relationship hint, `add column` → the
+    /// (as-yet-unauthored) column hint, never the wrong form.
+    #[test]
+    fn hint_key_resolves_the_typed_form() {
+        assert_eq!(
+            hint_key_for_input_in_mode("add 1:n relationship from A.x to B.y", Mode::Simple),
+            Some("add_relationship")
+        );
+        assert_eq!(
+            hint_key_for_input_in_mode("add column Note text to T", Mode::Simple),
+            Some("add_column")
+        );
+        assert_eq!(
+            hint_key_for_input_in_mode("insert into T values (1)", Mode::Simple),
+            Some("insert")
+        );
+        // Multi-form DROP disambiguates to the typed form too.
+        assert_eq!(
+            hint_key_for_input_in_mode("drop table T", Mode::Simple),
+            Some("drop_table")
+        );
+        // Unknown entry word → None (tier-2 fallback).
+        assert_eq!(hint_key_for_input_in_mode("zzz", Mode::Simple), None);
+    }
+}
+
 #[cfg(test)]
 mod usage_key_tests {
    use super::usage_key_for_input;
@@ -6910,6 +6910,7 @@ mod dispatch_3a_tests {
        shape: Node::Word(Word::keyword("dsltail")),
        ast_builder: dsl_builder,
        help_id: None,
+        hint_ids: &[],
        usage_ids: &[],
    };
    static SMOKE_SQL: CommandNode = CommandNode {
@@ -6917,6 +6918,7 @@ mod dispatch_3a_tests {
        shape: Node::Word(Word::keyword("sqltail")),
        ast_builder: sql_builder,
        help_id: None,
+        hint_ids: &[],
        usage_ids: &[],
    };

@@ -180,6 +180,7 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
    ("help.unknown_topic", &["topic"]),
    ("help.app.quit", &[]),
    ("help.app.help", &[]),
+    ("help.app.hint", &[]),
    ("help.app.rebuild", &[]),
    ("help.app.save", &[]),
    ("help.app.new", &[]),
@@ -222,6 +223,89 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
        &["message", "usage"],
    ),
    ("hint.ambient_expected", &["expected"]),
+    ("hint.getting_started", &[]),
+    // Tier-3 teaching blocks (ADR-0053 D3) — Phase-B exemplars.
+    ("hint.cmd.insert.what", &[]),
+    ("hint.cmd.insert.example", &[]),
+    ("hint.cmd.insert.concept", &[]),
+    ("hint.cmd.add_relationship.what", &[]),
+    ("hint.cmd.add_relationship.example", &[]),
+    ("hint.cmd.add_relationship.concept", &[]),
+    ("hint.err.foreign_key.child_side.what", &[]),
+    ("hint.err.foreign_key.child_side.example", &[]),
+    ("hint.err.foreign_key.child_side.concept", &[]),
+    // Phase C batch 1 — app-lifecycle command hints.
+    ("hint.cmd.quit.what", &[]),
+    ("hint.cmd.quit.example", &[]),
+    ("hint.cmd.help.what", &[]),
+    ("hint.cmd.help.example", &[]),
+    ("hint.cmd.help.concept", &[]),
+    ("hint.cmd.hint.what", &[]),
+    ("hint.cmd.hint.example", &[]),
+    ("hint.cmd.rebuild.what", &[]),
+    ("hint.cmd.rebuild.example", &[]),
+    ("hint.cmd.rebuild.concept", &[]),
+    ("hint.cmd.save.what", &[]),
+    ("hint.cmd.save.example", &[]),
+    ("hint.cmd.new.what", &[]),
+    ("hint.cmd.new.example", &[]),
+    ("hint.cmd.load.what", &[]),
+    ("hint.cmd.load.example", &[]),
+    ("hint.cmd.export.what", &[]),
+    ("hint.cmd.export.example", &[]),
+    ("hint.cmd.export.concept", &[]),
+    ("hint.cmd.import.what", &[]),
+    ("hint.cmd.import.example", &[]),
+    ("hint.cmd.mode.what", &[]),
+    ("hint.cmd.mode.example", &[]),
+    ("hint.cmd.mode.concept", &[]),
+    ("hint.cmd.messages.what", &[]),
+    ("hint.cmd.messages.example", &[]),
+    ("hint.cmd.messages.concept", &[]),
+    ("hint.cmd.undo.what", &[]),
+    ("hint.cmd.undo.example", &[]),
+    ("hint.cmd.undo.concept", &[]),
+    ("hint.cmd.redo.what", &[]),
+    ("hint.cmd.redo.example", &[]),
+    ("hint.cmd.copy.what", &[]),
+    ("hint.cmd.copy.example", &[]),
+    // Phase C batch 2 — DDL command hints.
+    ("hint.cmd.create_table.what", &[]),
+    ("hint.cmd.create_table.example", &[]),
+    ("hint.cmd.create_table.concept", &[]),
+    ("hint.cmd.create_m2n.what", &[]),
+    ("hint.cmd.create_m2n.example", &[]),
+    ("hint.cmd.create_m2n.concept", &[]),
+    ("hint.cmd.add_column.what", &[]),
+    ("hint.cmd.add_column.example", &[]),
+    ("hint.cmd.add_column.concept", &[]),
+    ("hint.cmd.add_index.what", &[]),
+    ("hint.cmd.add_index.example", &[]),
+    ("hint.cmd.add_index.concept", &[]),
+    ("hint.cmd.add_constraint.what", &[]),
+    ("hint.cmd.add_constraint.example", &[]),
+    ("hint.cmd.add_constraint.concept", &[]),
+    ("hint.cmd.drop_table.what", &[]),
+    ("hint.cmd.drop_table.example", &[]),
+    ("hint.cmd.drop_table.concept", &[]),
+    ("hint.cmd.drop_column.what", &[]),
+    ("hint.cmd.drop_column.example", &[]),
+    ("hint.cmd.drop_column.concept", &[]),
+    ("hint.cmd.drop_relationship.what", &[]),
+    ("hint.cmd.drop_relationship.example", &[]),
+    ("hint.cmd.drop_relationship.concept", &[]),
+    ("hint.cmd.drop_index.what", &[]),
+    ("hint.cmd.drop_index.example", &[]),
+    ("hint.cmd.drop_index.concept", &[]),
+    ("hint.cmd.drop_constraint.what", &[]),
+    ("hint.cmd.drop_constraint.example", &[]),
+    ("hint.cmd.drop_constraint.concept", &[]),
+    ("hint.cmd.rename_column.what", &[]),
+    ("hint.cmd.rename_column.example", &[]),
+    ("hint.cmd.rename_column.concept", &[]),
+    ("hint.cmd.change_column.what", &[]),
+    ("hint.cmd.change_column.example", &[]),
+    ("hint.cmd.change_column.concept", &[]),
    (
        "hint.ambient_invalid_ident",
        &["kind", "found"],
@@ -299,6 +383,7 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
    ("parse.usage.rename_column", &[]),
    ("parse.usage.export", &[]),
    ("parse.usage.help", &[]),
+    ("parse.usage.hint", &[]),
    ("parse.usage.import", &[]),
    ("parse.usage.copy", &[]),
    ("parse.usage.load", &[]),
@@ -35,7 +35,7 @@ pub mod translate;

 pub use error::{DiagnosticTable, FriendlyError};
 pub use format::{catalog, Catalog};
-pub use translate::{FailureContext, Operation, TranslateContext, Verbosity};
+pub use translate::{error_hint_class, FailureContext, Operation, TranslateContext, Verbosity};

 // `translate::translate` and `format::translate` are different
 // callables — the former is the structured DbError → FriendlyError
@@ -256,6 +256,8 @@ help:
    help: |-
        help                       — show this command list
        help <command>             — detailed help for one command (e.g. `help insert`)
+    hint: |-
+        hint                       — explain the most recent error (press F1 for a hint on what you're typing)
    rebuild: |-
        rebuild                    — rebuild the project database from project.yaml + data/ (with confirmation)
    save: |-
@@ -386,6 +388,129 @@ hint:
  ambient_complete: "Submit with Enter"
  ambient_expected: "Next: {expected}"
  ambient_error_with_usage: "{message} — usage: {usage}"
+  # H2 / ADR-0053: shown by `hint` / F1 when there is nothing specific
+  # to expand on (no recent error, empty input).
+  getting_started: "Start typing a command and press F1 for a hint, or type `help` for the full command list."
+  # ── Tier-3 teaching blocks (ADR-0053 D3) ──────────────────────────
+  # Per-form command hints (`hint.cmd.<form>`) and per-class error
+  # hints (`hint.err.<class>`), each a `what` (1–2 sentences) / `example`
+  # (one runnable, mode-correct line) / `concept` (the relational idea —
+  # the teaching part). Phase B seeds the three approved exemplars; the
+  # rest are authored in Phase C.
+  cmd:
+    insert:
+      what: "Add one or more rows to a table."
+      example: "insert into Customers values ('Ann', 'ann@example.io')"
+      concept: "A row is one record; each value lines up with a column, in order. Columns typed `serial`/`shortid` fill themselves — leave them out."
+    add_relationship:
+      what: "Link two tables so a parent row can own many child rows."
+      example: "add 1:n relationship from Customers.id to Orders.customer_id"
+      concept: "The \"1:n\" means one parent, many children. The child column holds the foreign key; add `--create-fk` to create that column if it doesn't exist yet."
+    # App-lifecycle commands (Phase C batch 1). Reference-leaning, so
+    # `concept` appears only where there's a real idea to teach.
+    quit:
+      what: "Leave the playground. Your project is already saved to disk."
+      example: "quit"
+    help:
+      what: "List every command, or show the detail for one."
+      example: "help insert"
+      concept: "`help` is the reference; press F1 while typing for a hint about the command you're building right now."
+    hint:
+      what: "Explain the most recent error — or, pressing F1 while typing, the command you're building."
+      example: "hint"
+    rebuild:
+      what: "Rebuild the project database from its saved text files."
+      example: "rebuild"
+      concept: "The text files (project.yaml + the data folder) are the source of truth; the database is derived and can always be rebuilt from them."
+    save:
+      what: "Save the current project under a name; `save as` copies it to a new one."
+      example: "save as my-shop"
+    new:
+      what: "Close the current project and start a fresh temporary one."
+      example: "new"
+    load:
+      what: "Open the project picker to switch to a saved project."
+      example: "load"
+    export:
+      what: "Write a shareable zip of the project — its text files only, never the database."
+      example: "export my-shop.zip"
+      concept: "The zip carries the schema and data as text, so anyone can rebuild the very same database from it."
+    import:
+      what: "Unpack a project zip into a new project and switch to it."
+      example: "import my-shop.zip as shop-copy"
+    mode:
+      what: "Switch between simple mode (the guided teaching commands) and advanced mode (raw SQL)."
+      example: "mode advanced"
+      concept: "Simple mode uses keyword commands; advanced mode lets you write SQL directly. A leading `:` runs a single advanced command without switching modes."
+    messages:
+      what: "Show or set how much detail error messages give."
+      example: "messages short"
+      concept: "Verbose (the default) adds a fix-it hint under each error headline; short shows just the headline."
+    undo:
+      what: "Undo the most recent change, after a confirmation."
+      example: "undo"
+      concept: "Every data or schema change is snapshotted first, so you can step back; `redo` re-applies what you undid."
+    redo:
+      what: "Re-apply the most recently undone change."
+      example: "redo"
+    copy:
+      what: "Copy the output panel to the clipboard — all of it, or just the last command's output."
+      example: "copy last"
+    # DDL — schema-shaping commands (Phase C batch 2).
+    create_table:
+      what: "Create a new table — its columns, their types, and a primary key."
+      example: "create table Customers with pk id(serial), name(text), email(text)"
+      concept: "A table is a set of rows that share the same columns. The primary key uniquely identifies each row; a `serial` key numbers the rows for you."
+    create_m2n:
+      what: "Create a junction table linking two tables many-to-many."
+      example: "create m:n relationship from Students to Courses"
+      concept: "A many-to-many link (a student takes many courses; a course has many students) can't live in either table, so it gets its own junction table holding a foreign key to each side."
+    add_column:
+      what: "Add a new column to an existing table."
+      example: "add column Customers: phone (text)"
+      concept: "Existing rows take the column's default, or null. A `not null` column with no default can't be added to a table that already has rows — there'd be nothing to put in them."
+    add_index:
+      what: "Create an index on one or more columns to speed up lookups."
+      example: "add index as idx_email on Customers (email)"
+      concept: "An index is a sorted side-structure that makes a lookup like `where email = …` fast, at the cost of a little space and slightly slower writes."
+    add_constraint:
+      what: "Add a constraint — not null, unique, default, or check — to an existing column."
+      example: "add constraint not null to Customers.email"
+      concept: "A constraint is a rule the database enforces on every row. Adding one fails if existing rows already break it, so you fix the data first."
+    drop_table:
+      what: "Remove a table and all of its rows."
+      example: "drop table Customers"
+      concept: "If other tables reference this one through a relationship, drop those relationships (or their child rows) first — the database won't orphan them."
+    drop_column:
+      what: "Remove a column from a table."
+      example: "drop column Customers: phone"
+      concept: "The column's values are lost. You can't drop a primary-key column, or one a relationship depends on."
+    drop_relationship:
+      what: "Remove a relationship between two tables."
+      example: "drop relationship customer_orders"
+      concept: "This drops the foreign-key link and stops the database enforcing it; the tables and their rows stay. The foreign-key column itself remains unless you also drop it."
+    drop_index:
+      what: "Remove an index by name."
+      example: "drop index idx_email"
+      concept: "Only the lookup shortcut goes — the data is untouched. Queries still work, just without that speed-up."
+    drop_constraint:
+      what: "Remove a constraint from a column."
+      example: "drop constraint not null from Customers.email"
+      concept: "The rule stops being enforced from now on; rows already stored are left as they are."
+    rename_column:
+      what: "Rename a column, keeping its values and type."
+      example: "rename column Customers: email to contact_email"
+      concept: "Only the name changes — the stored data is the same. References to the column are reconciled so nothing breaks."
+    change_column:
+      what: "Change a column's type, converting the existing values."
+      example: "change column Customers: status (int)"
+      concept: "The database converts each stored value to the new type; if a value can't convert it refuses the change, so you don't silently lose data. Flags let you force or skip the conversion."
+  err:
+    foreign_key:
+      child_side:
+        what: "The value you gave for the child column doesn't match any parent row, so the foreign key has nothing to point at."
+        example: "First insert the parent (insert into Customers …), then the child that references it."
+        concept: "A foreign key is a promise that every child points at a real parent, so the parent must exist first. To allow orphans on delete instead, set the relationship's `on delete` to `set null` or `cascade`."
  # Invalid identifier in a schema slot (ADR-0022 stage 8e
  # + the user's #5). Voice mirrors ADR-0019's "no such
  # {kind}" wording for consistency with engine errors.
@@ -617,6 +742,7 @@ parse:
    # description.
    quit: "quit"
    help: "help [<command>]"
+    hint: "hint"
    rebuild: "rebuild"
    save: "save  |  save as"
    new: "new"
@@ -253,6 +253,73 @@ pub fn translate(error: &DbError, ctx: &TranslateContext) -> FriendlyError {
    fe
 }

+/// The tier-3 hint class (`hint.err.<class>`) for an error.
+///
+/// The same classification [`translate`] performs, surfaced as a
+/// stable key for the contextual `hint` (H2 / ADR-0053 D5). Returns
+/// `None` for internal / fatal errors that carry no learner-facing
+/// hint (persistence, IO, worker-gone).
+///
+/// **Keep in sync with [`translate`] / `translate_sqlite` /
+/// `translate_constraint` / `translate_foreign_key`** — the unit tests
+/// below pin each class.
+#[must_use]
+pub fn error_hint_class(error: &DbError, ctx: &TranslateContext) -> Option<&'static str> {
+    match error {
+        DbError::Sqlite { message, kind } => sqlite_hint_class(message, *kind, ctx),
+        DbError::Unsupported(_) | DbError::InvalidValue(_) => Some("invalid_value"),
+        DbError::PersistenceFatal { .. }
+        | DbError::RebuildRowFailed { .. }
+        | DbError::Io(_)
+        | DbError::WorkerGone => None,
+    }
+}
+
+fn sqlite_hint_class(
+    message: &str,
+    kind: SqliteErrorKind,
+    ctx: &TranslateContext,
+) -> Option<&'static str> {
+    if matches!(ctx.operation, Some(Operation::ChangeColumnType)) {
+        return Some("type_mismatch");
+    }
+    Some(match kind {
+        SqliteErrorKind::NoSuchTable | SqliteErrorKind::NoSuchColumn => "not_found",
+        SqliteErrorKind::AlreadyExists => "already_exists",
+        SqliteErrorKind::UniqueViolation => constraint_hint_class(message, ctx),
+        SqliteErrorKind::Other => "generic",
+    })
+}
+
+fn constraint_hint_class(message: &str, ctx: &TranslateContext) -> &'static str {
+    let lower = message.to_ascii_lowercase();
+    if lower.contains("unique constraint failed") {
+        "unique"
+    } else if lower.contains("foreign key constraint failed") {
+        fk_hint_class(ctx)
+    } else if lower.contains("not null constraint failed") {
+        "not_null"
+    } else if lower.contains("check constraint failed") {
+        "check"
+    } else {
+        "generic"
+    }
+}
+
+const fn fk_hint_class(ctx: &TranslateContext) -> &'static str {
+    // Mirrors `translate_foreign_key`'s side disambiguation.
+    if ctx.parent_table.is_some() {
+        return "foreign_key.child_side";
+    }
+    if ctx.child_table.is_some() {
+        return "foreign_key.parent_side";
+    }
+    match ctx.operation {
+        Some(Operation::Delete) => "foreign_key.parent_side",
+        _ => "foreign_key.child_side",
+    }
+}
+
 fn translate_sqlite(
    message: &str,
    kind: SqliteErrorKind,
@@ -798,6 +865,92 @@ mod tests {
        }
    }

+    // ── H2 / ADR-0053: error → tier-3 hint class ────────────────
+
+    #[test]
+    fn hint_class_maps_runtime_error_kinds() {
+        use crate::db::{DbError, SqliteErrorKind};
+        let sqlite = |kind, msg: &str| DbError::Sqlite {
+            message: msg.to_string(),
+            kind,
+        };
+        let d = TranslateContext::default;
+        assert_eq!(
+            error_hint_class(&sqlite(SqliteErrorKind::NoSuchTable, "no such table: X"), &d()),
+            Some("not_found")
+        );
+        assert_eq!(
+            error_hint_class(&sqlite(SqliteErrorKind::NoSuchColumn, "no such column: X"), &d()),
+            Some("not_found")
+        );
+        assert_eq!(
+            error_hint_class(&sqlite(SqliteErrorKind::AlreadyExists, "already exists"), &d()),
+            Some("already_exists")
+        );
+        assert_eq!(
+            error_hint_class(&sqlite(SqliteErrorKind::Other, "boom"), &d()),
+            Some("generic")
+        );
+        // Constraint-violation message splitting.
+        let cv = |msg: &str| sqlite(SqliteErrorKind::UniqueViolation, msg);
+        assert_eq!(
+            error_hint_class(&cv("UNIQUE constraint failed: T.c"), &d()),
+            Some("unique")
+        );
+        assert_eq!(
+            error_hint_class(&cv("NOT NULL constraint failed: T.c"), &d()),
+            Some("not_null")
+        );
+        assert_eq!(
+            error_hint_class(&cv("CHECK constraint failed: T"), &d()),
+            Some("check")
+        );
+        // change-column op routes any engine error to type_mismatch.
+        assert_eq!(
+            error_hint_class(
+                &sqlite(SqliteErrorKind::Other, "x"),
+                &ctx_with(Operation::ChangeColumnType)
+            ),
+            Some("type_mismatch")
+        );
+        // App-level refusals and internal/fatal errors.
+        assert_eq!(
+            error_hint_class(&DbError::InvalidValue("bad".to_string()), &d()),
+            Some("invalid_value")
+        );
+        assert_eq!(error_hint_class(&DbError::WorkerGone, &d()), None);
+    }
+
+    #[test]
+    fn hint_class_resolves_foreign_key_sides() {
+        use crate::db::{DbError, SqliteErrorKind};
+        let fk = || DbError::Sqlite {
+            message: "FOREIGN KEY constraint failed".to_string(),
+            kind: SqliteErrorKind::UniqueViolation,
+        };
+        // Enrichment: parent_table populated → child-side.
+        let ctx = TranslateContext {
+            parent_table: Some("Parent".to_string()),
+            ..TranslateContext::default()
+        };
+        assert_eq!(error_hint_class(&fk(), &ctx), Some("foreign_key.child_side"));
+        // child_table populated → parent-side.
+        let ctx = TranslateContext {
+            child_table: Some("Child".to_string()),
+            ..TranslateContext::default()
+        };
+        assert_eq!(error_hint_class(&fk(), &ctx), Some("foreign_key.parent_side"));
+        // No enrichment: operation is the tiebreaker.
+        assert_eq!(
+            error_hint_class(&fk(), &ctx_with(Operation::Delete)),
+            Some("foreign_key.parent_side")
+        );
+        assert_eq!(
+            error_hint_class(&fk(), &ctx_with(Operation::Insert)),
+            Some("foreign_key.child_side")
+        );
+    }
+
    fn sqlite(message: &str, kind: SqliteErrorKind) -> DbError {
        DbError::Sqlite {
            message: message.to_string(),
@@ -1190,7 +1190,7 @@ async fn build_schema_cache(database: &Database) -> crate::completion::SchemaCac
    // miss leaves that table's columns unpopulated and the
    // walker falls back to the schemaless value-literal list.
    for name in cache.tables.clone() {
-        if let Ok(desc) = database.describe_table(name.clone(), None).await {
+        if let Ok(desc) = database.describe_table(name.clone()).await {
            // Per-table indexes for the items panel (S2, ADR-0025).
            // Carry uniqueness so the panel can mark a UNIQUE index
            // (ADR-0035 §4d). Captured before `desc.columns` is
@@ -1650,7 +1650,7 @@ async fn build_show_data_echo(
            limit: Some(_),
            ..
        } => database
-            .describe_table(name.clone(), None)
+            .describe_table(name.clone())
            .await
            .map(|desc| {
                desc.columns
@@ -1732,7 +1732,7 @@ async fn collect_echo_lookups(
        Command::DropIndex {
            selector: IndexSelector::Columns { table, columns },
        } => {
-            if let Ok(desc) = database.describe_table(table.clone(), None).await
+            if let Ok(desc) = database.describe_table(table.clone()).await
                && let Some(idx) = desc.indexes.iter().find(|i| i.columns == *columns)
            {
                out.drop_index_name = Some(idx.name.clone());
@@ -1747,7 +1747,7 @@ async fn collect_echo_lookups(
                    child_column,
                },
        } => {
-            if let Ok(desc) = database.describe_table(child_table.clone(), None).await
+            if let Ok(desc) = database.describe_table(child_table.clone()).await
                && let Some(rel) = desc.outbound_relationships.iter().find(|r| {
                    // The Endpoints drop selector is single-column
                    // (ADR-0043 keeps DROP by-endpoints single-column;
@@ -1771,7 +1771,7 @@ async fn collect_echo_lookups(
            // resolver API would be the next step if schemas grow.
            if let Ok(tables) = database.list_tables().await {
                for table in tables {
-                    if let Ok(desc) = database.describe_table(table.clone(), None).await
+                    if let Ok(desc) = database.describe_table(table.clone()).await
                        && desc.outbound_relationships.iter().any(|r| r.name == *name)
                    {
                        out.drop_relationship = Some((name.clone(), table.clone()));
@@ -1795,8 +1795,8 @@ async fn collect_echo_lookups(
            // *before* execution to know which `ADD COLUMN` lines to
            // emit. The parent columns here are the explicit DSL list,
            // paired positionally with the child list.
-            let parent_desc = database.describe_table(parent_table.clone(), None).await;
-            let child_desc = database.describe_table(child_table.clone(), None).await;
+            let parent_desc = database.describe_table(parent_table.clone()).await;
+            let child_desc = database.describe_table(child_table.clone()).await;
            if let (Ok(parent_desc), Ok(child_desc)) = (parent_desc, child_desc) {
                let mut new_columns: Vec<(String, crate::dsl::types::Type)> = Vec::new();
                for (child_col, parent_col) in child_columns.iter().zip(parent_columns) {
@@ -2064,7 +2064,7 @@ async fn enrich_check_violation(
        .await
        .map(|v| v.to_string());
    // The rule itself — the column's compiled CHECK expression.
-    if let Ok(desc) = database.describe_table(table.to_string(), None).await
+    if let Ok(desc) = database.describe_table(table.to_string()).await
        && let Some(col) = desc.columns.iter().find(|c| c.name == column)
    {
        facts.check_rule.clone_from(&col.check);
@@ -2272,7 +2272,7 @@ async fn user_value_for_column_with_schema(
    } = command
    {
        let desc = database
-            .describe_table(table.to_string(), None)
+            .describe_table(table.to_string())
            .await
            .ok()?;
        // Build the natural-order column list the same way
@@ -2311,7 +2311,7 @@ async fn user_value_for_column_with_schema(
        && literal_rows.len() == 1
    {
        let desc = database
-            .describe_table(table.to_string(), None)
+            .describe_table(table.to_string())
            .await
            .ok()?;
        let idx = desc.columns.iter().position(|c| c.name == column)?;
@@ -2930,7 +2930,7 @@ async fn execute_command_typed(
            .await
            .map(|d| CommandOutcome::Schema(Some(d))),
        Command::ShowTable { name } => database
-            .describe_table(name, src)
+            .describe_table(name)
            .await
            .map(|d| CommandOutcome::Schema(Some(d))),
        // ADR-0044: a named relationship renders as a diagram (App-side),
@@ -2983,14 +2983,14 @@ async fn execute_command_typed(
            filter,
            limit,
        } => database
-            .query_data(name, filter, limit, src)
+            .query_data(name, filter, limit)
            .await
            .map(CommandOutcome::Query),
        // A SQL `SELECT` (advanced mode; ADR-0030 §6, ADR-0031).
        // The grammar walker has already validated `sql` is in
        // the supported subset; the worker runs it as text.
        Command::Select { sql } => database
-            .run_select(sql, src)
+            .run_select(sql)
            .await
            .map(CommandOutcome::Query),
        // A SQL `INSERT` (advanced mode; ADR-0033 §1). Grammar-as-
@@ -93,7 +93,7 @@ fn rename_column_with_case_variant_table_keeps_metadata_in_step() {
    .expect("rename column via a case-variant table name");

    let desc = r
-        .block_on(db.describe_table("Items".to_string(), None))
+        .block_on(db.describe_table("Items".to_string()))
        .expect("describe Items");
    let amount = desc
        .columns
@@ -126,7 +126,7 @@ fn insert_with_case_variant_table_persists_and_survives_rebuild() {

    let db = fresh_rebuild(db, &project, &r);
    let rows = r
-        .block_on(db.query_data("Items".to_string(), None, None, None))
+        .block_on(db.query_data("Items".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(rows.len(), 1, "the wrong-case insert survived the rebuild (no data loss)");
@@ -146,7 +146,7 @@ fn add_column_with_case_variant_table_survives_rebuild() {
    );

    let db = fresh_rebuild(db, &project, &r);
-    let desc = r.block_on(db.describe_table("Items".to_string(), None)).expect("describe");
+    let desc = r.block_on(db.describe_table("Items".to_string())).expect("describe");
    let qty = desc.columns.iter().find(|c| c.name == "qty").expect("qty added");
    assert_eq!(qty.user_type, Some(Type::Int), "qty's user-type survived the rebuild");
    // The CHECK is intact too (a negative qty is refused under the real table).
@@ -224,12 +224,12 @@ fn add_relationship_with_case_variant_tables_survives_rebuild() {
         add 1:n relationship from parent.id to child.parent_id\n",
    );
    // The parent's inbound relationship is visible under the stored case.
-    let p = r.block_on(db.describe_table("Parent".to_string(), None)).expect("describe Parent");
+    let p = r.block_on(db.describe_table("Parent".to_string())).expect("describe Parent");
    assert_eq!(p.inbound_relationships.len(), 1, "relationship recorded under the stored case");
    assert_eq!(p.inbound_relationships[0].other_table, "Child");

    let db = fresh_rebuild(db, &project, &r);
-    let p = r.block_on(db.describe_table("Parent".to_string(), None)).expect("describe Parent");
+    let p = r.block_on(db.describe_table("Parent".to_string())).expect("describe Parent");
    assert_eq!(p.inbound_relationships.len(), 1, "relationship survived the rebuild");
    assert_eq!(p.inbound_relationships[0].other_table, "Child");
 }
@@ -276,7 +276,7 @@ fn compound_fk_declares_enforces_and_round_trips() {
        );

        // describe shows the compound endpoints symmetrically.
-        let city = db.describe_table("City".to_string(), None).await.unwrap();
+        let city = db.describe_table("City".to_string()).await.unwrap();
        let outbound = &city.outbound_relationships[0];
        assert_eq!(
            outbound.local_columns,
@@ -329,7 +329,7 @@ fn compound_fk_create_fk_makes_both_child_columns() {
        )
        .await
        .expect("add compound relationship with --create-fk");
-        let city = db.describe_table("City".to_string(), None).await.unwrap();
+        let city = db.describe_table("City".to_string()).await.unwrap();
        for col in ["c_country", "c_code"] {
            assert!(
                city.columns.iter().any(|c| c.name == col),
@@ -527,7 +527,7 @@ fn compound_fk_survives_rebuild_from_text() {
            .await;
        assert!(bad.is_err(), "compound FK still enforced after rebuild from text");
        // Endpoints survived the round-trip intact.
-        let city = db.describe_table("City".to_string(), None).await.unwrap();
+        let city = db.describe_table("City".to_string()).await.unwrap();
        assert_eq!(
            city.outbound_relationships[0].other_columns,
            vec!["country".to_string(), "code".to_string()],
@@ -563,7 +563,7 @@ fn compound_fk_undo_removes_the_relationship() {
        .await
        .expect("add compound relationship");
        assert_eq!(
-            db.describe_table("City".to_string(), None)
+            db.describe_table("City".to_string())
                .await
                .unwrap()
                .outbound_relationships
@@ -573,7 +573,7 @@ fn compound_fk_undo_removes_the_relationship() {
        // One undo step removes the whole relationship (ADR-0013/0006).
        db.undo().await.unwrap().expect("undo applied");
        assert!(
-            db.describe_table("City".to_string(), None)
+            db.describe_table("City".to_string())
                .await
                .unwrap()
                .outbound_relationships
@@ -76,7 +76,7 @@ fn rebuild_restores_schema_only_project() {

    // Phase 4: confirm Customers exists with the right shape.
    let desc = rt()
-        .block_on(async { db.describe_table("Customers".to_string(), None).await })
+        .block_on(async { db.describe_table("Customers".to_string()).await })
        .expect("describe_table");
    assert_eq!(desc.name, "Customers");
    let cols: Vec<&str> = desc.columns.iter().map(|c| c.name.as_str()).collect();
@@ -143,7 +143,7 @@ fn rebuild_restores_rows_from_csv() {
    });

    let rows = rt()
-        .block_on(async { db.query_data("Customers".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("Customers".to_string(), None, None).await })
        .expect("query_data");
    assert_eq!(rows.rows.len(), 2);
    let names: Vec<Option<String>> = rows.rows.iter().map(|r| r[1].clone()).collect();
@@ -371,7 +371,7 @@ fn rebuild_preserves_created_at_from_yaml() {
    // Trigger any successful command so project.yaml is
    // rewritten from the now-rebuilt db state.
    rt().block_on(async {
-        db.describe_table("T".to_string(), Some("show table T".to_string()))
+        db.describe_table("T".to_string())
            .await
            .unwrap();
        // describe is read-only; force a rewrite by adding a column.
@@ -451,7 +451,7 @@ fn rebuild_restores_indexes() {
    });

    let desc = rt()
-        .block_on(async { db.describe_table("Customers".to_string(), None).await })
+        .block_on(async { db.describe_table("Customers".to_string()).await })
        .expect("describe_table");
    assert_eq!(desc.indexes.len(), 1, "index should survive rebuild");
    assert_eq!(desc.indexes[0].name, "idx_email");
@@ -173,7 +173,7 @@ fn rebuild_against_populated_db_wipes_and_reloads() {
            .expect("rebuild");
    });
    let rows = rt()
-        .block_on(async { db.query_data("Customers".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("Customers".to_string(), None, None).await })
        .unwrap();
    assert_eq!(rows.rows.len(), 1);
    assert_eq!(rows.rows[0][1].as_deref(), Some("Edna"));
@@ -362,7 +362,7 @@ fn end_to_end_export_then_import_real_project() {

    // Round-trip: the inserted row is back.
    let data_view = rt()
-        .block_on(async { imported_db.query_data("Customers".to_string(), None, None, None).await })
+        .block_on(async { imported_db.query_data("Customers".to_string(), None, None).await })
        .expect("query data");
    assert_eq!(data_view.rows.len(), 1);
    // Serial id auto-filled to 1; Name was the inserted value.
@@ -107,7 +107,7 @@ fn generates_junction_with_compound_pk_and_two_enforced_fks() {
        assert!(tables.contains(&"Students_Courses".to_string()), "tables: {tables:?}");

        // Two FK columns, both part of the compound PK.
-        let desc = db.describe_table("Students_Courses".to_string(), None).await.unwrap();
+        let desc = db.describe_table("Students_Courses".to_string()).await.unwrap();
        let cols: Vec<(&str, bool)> =
            desc.columns.iter().map(|c| (c.name.as_str(), c.primary_key)).collect();
        assert_eq!(
@@ -191,7 +191,7 @@ fn compound_parent_pk_contributes_one_fk_column_each() {
            .await
            .expect("create m:n");

-        let desc = db.describe_table("Students_Sections".to_string(), None).await.unwrap();
+        let desc = db.describe_table("Students_Sections".to_string()).await.unwrap();
        let names: Vec<&str> = desc.columns.iter().map(|c| c.name.as_str()).collect();
        assert_eq!(names, vec!["Students_id", "Sections_course_id", "Sections_term"]);
        // All three form the compound PK.
@@ -221,7 +221,7 @@ fn deleting_a_parent_cascades_to_the_junction() {

        // Deleting the student cascades to the junction (ON DELETE CASCADE).
        db.delete("Students".to_string(), RowFilter::AllRows, None).await.unwrap();
-        let rows = db.query_data("Students_Courses".to_string(), None, None, None).await.unwrap();
+        let rows = db.query_data("Students_Courses".to_string(), None, None).await.unwrap();
        assert!(rows.rows.is_empty(), "junction rows should cascade-delete, got {:?}", rows.rows);
    });
 }
@@ -249,7 +249,7 @@ fn create_m2n_is_one_undo_step() {
        let tables = db.list_tables().await.unwrap();
        assert!(!tables.contains(&"Students_Courses".to_string()), "undo should remove the junction: {tables:?}");
        // The parents' relationships are gone too (the junction held them).
-        let students = db.describe_table("Students".to_string(), None).await.unwrap();
+        let students = db.describe_table("Students".to_string()).await.unwrap();
        assert!(students.inbound_relationships.is_empty(), "no leftover relationship after undo");
    });
 }
@@ -321,7 +321,7 @@ fn the_junction_can_be_renamed() {
        assert!(tables.contains(&"Enrollments".to_string()), "tables: {tables:?}");
        assert!(!tables.contains(&"Students_Courses".to_string()));
        // Both relationships survive the rename (rebuild-preserving).
-        let desc = db.describe_table("Enrollments".to_string(), None).await.unwrap();
+        let desc = db.describe_table("Enrollments".to_string()).await.unwrap();
        assert_eq!(desc.outbound_relationships.len(), 2, "FKs preserved across rename");
    });
 }
@@ -362,7 +362,7 @@ fn junction_survives_save_and_rebuild() {
        db.rebuild_from_text(project.path().to_path_buf(), None).await.expect("rebuild");
        let tables = db.list_tables().await.unwrap();
        assert!(tables.contains(&"Students_Courses".to_string()), "junction survived: {tables:?}");
-        let desc = db.describe_table("Students_Courses".to_string(), None).await.unwrap();
+        let desc = db.describe_table("Students_Courses".to_string()).await.unwrap();
        assert_eq!(desc.outbound_relationships.len(), 2, "both FKs reconstructed");
        assert!(desc.columns.iter().all(|c| c.primary_key), "compound PK reconstructed");
    });
@@ -108,13 +108,13 @@ fn replay_runs_advanced_sql_create_table_as_a_write() {

    // The SQL DDL line actually created the structural table…
    let desc = rt()
-        .block_on(async { db.describe_table("Widget".to_string(), None).await })
+        .block_on(async { db.describe_table("Widget".to_string()).await })
        .expect("describe");
    let names: Vec<String> = desc.columns.iter().map(|c| c.name.clone()).collect();
    assert_eq!(names, vec!["id".to_string(), "name".to_string()]);
    // …and the following insert (serial id auto-filled) ran against it.
    let rows = rt()
-        .block_on(async { db.query_data("Widget".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("Widget".to_string(), None, None).await })
        .expect("query")
        .rows;
    assert_eq!(rows.len(), 1);
@@ -139,7 +139,7 @@ fn replay_three_lines_dispatches_three_commands() {

    // The dispatched commands actually mutated state.
    let data_result = rt()
-        .block_on(async { db.query_data("T".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("T".to_string(), None, None).await })
        .expect("query_data");
    assert_eq!(data_result.rows.len(), 1, "row inserted");
    assert_eq!(data_result.rows[0][1].as_deref(), Some("Alice"));
@@ -174,7 +174,7 @@ fn replay_of_actual_history_log_runs_ok_commands_and_skips_err() {
    assert_completed(&events, 3);

    let data_result = rt()
-        .block_on(async { db.query_data("T".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("T".to_string(), None, None).await })
        .expect("query_data");
    assert_eq!(data_result.rows.len(), 1, "only the ok INSERT applied");
    assert_eq!(data_result.rows[0][1].as_deref(), Some("alpha"));
@@ -227,7 +227,7 @@ fn replay_skips_app_lifecycle_commands_silently() {
        other => panic!("expected ReplayCompleted, got {other:?}"),
    }
    let data_result = rt()
-        .block_on(async { db.query_data("T".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("T".to_string(), None, None).await })
        .expect("query_data");
    assert!(
        data_result.columns.iter().any(|c| c == "v"),
@@ -401,14 +401,14 @@ fn replay_aborts_on_first_parse_failure_and_reports_line() {
    // but earlier commands stayed applied (table T exists with
    // the `name` column).
    let desc = rt()
-        .block_on(async { db.describe_table("T".to_string(), None).await })
+        .block_on(async { db.describe_table("T".to_string()).await })
        .expect("describe_table");
    assert!(
        desc.columns.iter().any(|c| c.name == "name"),
        "earlier add column should have stayed applied"
    );
    let data_result = rt()
-        .block_on(async { db.query_data("T".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("T".to_string(), None, None).await })
        .expect("query_data");
    assert!(
        data_result.rows.is_empty(),
@@ -467,7 +467,7 @@ fn replay_rejects_wrong_type_value_in_a_hand_built_script() {
    // The earlier two lines stayed applied; the failing insert
    // did not run — state is intact.
    let data_result = rt()
-        .block_on(async { db.query_data("T".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("T".to_string(), None, None).await })
        .expect("query_data");
    assert!(
        data_result.rows.is_empty(),
@@ -527,7 +527,7 @@ fn replay_skips_nested_replay_with_a_warning() {
        other => panic!("expected ReplayCompleted (nested replay skipped), got {other:?}"),
    }
    // The nested file's table was NOT created (the replay was skipped).
-    let cols = rt().block_on(async { db.query_data("T".to_string(), None, None, None).await });
+    let cols = rt().block_on(async { db.query_data("T".to_string(), None, None).await });
    assert!(cols.is_err(), "inner.commands' table T must not exist (nested replay skipped)");
 }

@@ -462,7 +462,7 @@ fn app_show_table_renders_relationships_as_compact_diagrams() {
    rt.block_on(seed_schema(&db));
    // Orders holds the FK to Customers — an outbound relationship.
    let desc = rt
-        .block_on(db.describe_table("Orders".to_string(), None))
+        .block_on(db.describe_table("Orders".to_string()))
        .expect("describe Orders");

    let mut app = App::new();
@@ -111,7 +111,7 @@ fn e2e_alter_drop_compound_primary_key_member_is_refused() {

 /// The current user-facing type of column `name` in table `T`.
 fn col_type(db: &Database, r: &tokio::runtime::Runtime, name: &str) -> Option<Type> {
-    r.block_on(db.describe_table("T".to_string(), None))
+    r.block_on(db.describe_table("T".to_string()))
        .expect("describe")
        .columns
        .into_iter()
@@ -120,7 +120,7 @@ fn col_type(db: &Database, r: &tokio::runtime::Runtime, name: &str) -> Option<Ty
 }

 fn column_names(db: &Database, r: &tokio::runtime::Runtime) -> Vec<String> {
-    r.block_on(db.describe_table("T".to_string(), None))
+    r.block_on(db.describe_table("T".to_string()))
        .expect("describe")
        .columns
        .into_iter()
@@ -163,7 +163,7 @@ fn e2e_alter_table_add_rename_drop_and_raw_default_check() {

    // The DEFAULT backfilled the pre-existing row to qty = 0.
    let rows = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(rows.len(), 1);
@@ -252,7 +252,7 @@ fn e2e_alter_column_type_clean_and_lossy_convert() {
    }

    let rows = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(rows.len(), 1);
@@ -292,7 +292,7 @@ fn e2e_alter_column_type_int_to_serial_is_allowed() {
    }
    assert_eq!(col_type(&db, &r, "n"), Some(Type::Serial), "int→serial converted the column");
    let rows = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(rows[0][1].as_deref(), Some("100"), "the existing value is preserved");
@@ -635,7 +635,7 @@ fn e2e_drop_composite_unique_is_one_undo_step() {
    .expect("write");
    r.block_on(run_replay(&db, project.path(), "u.commands"));
    let has_unique = || {
-        !r.block_on(db.describe_table("T".to_string(), None))
+        !r.block_on(db.describe_table("T".to_string()))
            .expect("describe")
            .unique_constraints
            .is_empty()
@@ -878,7 +878,7 @@ fn e2e_describe_shows_table_level_constraints() {
        "events: {events:?}"
    );

-    let desc = r.block_on(db.describe_table("T".to_string(), None)).expect("describe");
+    let desc = r.block_on(db.describe_table("T".to_string())).expect("describe");
    assert_eq!(
        desc.unique_constraints,
        vec![vec!["a".to_string(), "b".to_string()]],
@@ -976,7 +976,7 @@ fn e2e_rename_table_with_rows_csv_follows_and_survives_rebuild() {
    assert!(!csv_path(&project, "Orders").exists(), "data/Orders.csv removed");

    let rows = r
-        .block_on(db.query_data("Purchases".to_string(), None, None, None))
+        .block_on(db.query_data("Purchases".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(rows.len(), 2);
@@ -991,7 +991,7 @@ fn e2e_rename_table_with_rows_csv_follows_and_survives_rebuild() {
        "Purchases round-tripped through a fresh rebuild: {tables:?}"
    );
    let rows = r
-        .block_on(db.query_data("Purchases".to_string(), None, None, None))
+        .block_on(db.query_data("Purchases".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(rows.len(), 2);
@@ -1077,7 +1077,7 @@ fn e2e_rename_fk_parent_updates_metadata_and_still_enforces() {
    );

    // The child's outbound relationship now points at the new parent name.
-    let c = r.block_on(db.describe_table("C".to_string(), None)).expect("describe C");
+    let c = r.block_on(db.describe_table("C".to_string())).expect("describe C");
    assert_eq!(c.outbound_relationships.len(), 1);
    assert_eq!(c.outbound_relationships[0].other_table, "Parent");

@@ -1129,7 +1129,7 @@ fn e2e_rename_fk_child_updates_metadata_and_still_enforces() {
    );

    // The parent's inbound relationship now names the renamed child.
-    let p = r.block_on(db.describe_table("P".to_string(), None)).expect("describe P");
+    let p = r.block_on(db.describe_table("P".to_string())).expect("describe P");
    assert_eq!(p.inbound_relationships.len(), 1);
    assert_eq!(p.inbound_relationships[0].other_table, "Child");

@@ -1168,7 +1168,7 @@ fn e2e_rename_self_referential_table_updates_both_ends() {
    );

    // Both ends of the self-reference now name `Tree`.
-    let t = r.block_on(db.describe_table("Tree".to_string(), None)).expect("describe Tree");
+    let t = r.block_on(db.describe_table("Tree".to_string())).expect("describe Tree");
    assert_eq!(t.outbound_relationships[0].other_table, "Tree");
    assert_eq!(t.inbound_relationships[0].other_table, "Tree");

@@ -1216,7 +1216,7 @@ fn e2e_rename_table_keeps_its_index_with_a_stale_name() {
        "events: {events:?}"
    );

-    let u = r.block_on(db.describe_table("Users".to_string(), None)).expect("describe Users");
+    let u = r.block_on(db.describe_table("Users".to_string())).expect("describe Users");
    assert_eq!(u.indexes.len(), 1, "the index followed the rename");
    assert_eq!(
        u.indexes[0].name, "T_email_idx",
@@ -1226,7 +1226,7 @@ fn e2e_rename_table_keeps_its_index_with_a_stale_name() {

    // Survives a fresh rebuild (recreated from IndexSchema on table Users).
    let db = fresh_rebuild(db, &project, &r);
-    let u = r.block_on(db.describe_table("Users".to_string(), None)).expect("describe Users");
+    let u = r.block_on(db.describe_table("Users".to_string())).expect("describe Users");
    assert_eq!(u.indexes.len(), 1);
    assert_eq!(u.indexes[0].name, "T_email_idx");
 }
@@ -1255,7 +1255,7 @@ fn e2e_rename_table_is_one_undo_step() {
        "undo restored the old table name: {tables:?}"
    );
    assert_eq!(
-        r.block_on(db.query_data("Orders".to_string(), None, None, None)).expect("query").rows.len(),
+        r.block_on(db.query_data("Orders".to_string(), None, None)).expect("query").rows.len(),
        1,
        "the row is back under the old name"
    );
@@ -1427,7 +1427,7 @@ fn e2e_alter_column_set_default_applies() {
    ))
    .expect("insert omitting qty");
    let rows = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(
@@ -1473,7 +1473,7 @@ fn e2e_alter_column_drop_default_removes_it() {
    ))
    .expect("insert omitting qty");
    let rows = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(
@@ -55,7 +55,7 @@ fn insert_row(db: &Database, r: &tokio::runtime::Runtime, id: i64, email: &str)
 }

 fn index(db: &Database, r: &tokio::runtime::Runtime, name: &str) -> Option<(Vec<String>, bool)> {
-    r.block_on(db.describe_table("T".to_string(), None))
+    r.block_on(db.describe_table("T".to_string()))
        .expect("describe")
        .indexes
        .into_iter()
@@ -64,7 +64,7 @@ fn created_table_appears_with_playground_types() {
    assert!(tables.contains(&"Widget".to_string()));

    let desc = r
-        .block_on(db.describe_table("Widget".to_string(), None))
+        .block_on(db.describe_table("Widget".to_string()))
        .expect("describe");
    let types: Vec<(String, Option<Type>)> = desc
        .columns
@@ -98,7 +98,7 @@ fn integer_primary_key_is_plain_int() {
    ))
    .expect("create");
    let desc = r
-        .block_on(db.describe_table("T".to_string(), None))
+        .block_on(db.describe_table("T".to_string()))
        .expect("describe");
    assert_eq!(desc.columns[0].user_type, Some(Type::Int));
 }
@@ -137,7 +137,7 @@ fn serial_pk_autoincrements_in_multi_column_table() {
    }

    let data = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query");
    let id_idx = data
        .columns
@@ -220,7 +220,7 @@ fn table_without_primary_key_is_allowed() {
    ))
    .expect("insert into PK-less table");
    let data = r
-        .block_on(db.query_data("Notes".to_string(), None, None, None))
+        .block_on(db.query_data("Notes".to_string(), None, None))
        .expect("query");
    assert_eq!(data.rows.len(), 1);
 }
@@ -299,7 +299,7 @@ fn default_is_applied_when_column_omitted() {
    ))
    .expect("insert");
    let data = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query");
    let n_idx = data.columns.iter().position(|c| c == "n").expect("n column");
    assert_eq!(data.rows[0][n_idx].as_deref(), Some("7"), "DEFAULT 7 applied");
@@ -381,7 +381,7 @@ fn check_default_and_composite_unique_survive_rebuild() {
    // A valid row inserts; DEFAULT n=7 survived.
    r.block_on(ins("1", "1", "5")).expect("valid row");
    let data = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query");
    let n_idx = data.columns.iter().position(|c| c == "n").expect("n column");
    assert_eq!(data.rows[0][n_idx].as_deref(), Some("7"), "DEFAULT survived rebuild");
@@ -679,7 +679,7 @@ fn sql_create_table_is_one_undo_step() {
 /// Sorted `id` column values of table `T`.
 fn ids(db: &Database, r: &tokio::runtime::Runtime) -> Vec<Option<String>> {
    let d = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query");
    let idx = d.columns.iter().position(|c| c == "id").expect("id column");
    let mut v: Vec<Option<String>> = d.rows.iter().map(|row| row[idx].clone()).collect();
@@ -801,7 +801,7 @@ fn dropping_a_column_a_table_check_references_fails_cleanly() {

    // The table is intact: both columns survive (rollback) ...
    let desc = r
-        .block_on(db.describe_table("T".to_string(), None))
+        .block_on(db.describe_table("T".to_string()))
        .expect("describe still works");
    assert_eq!(
        desc.columns.iter().map(|c| c.name.clone()).collect::<Vec<_>>(),
@@ -925,14 +925,14 @@ fn foreign_key_creates_named_relationship_visible_in_describe() {
    .expect("create child with FK");

    // The child has an outbound relationship; the parent an inbound one.
-    let child = r.block_on(db.describe_table("child".to_string(), None)).expect("describe child");
+    let child = r.block_on(db.describe_table("child".to_string())).expect("describe child");
    assert_eq!(child.outbound_relationships.len(), 1, "child references parent");
    let rel = &child.outbound_relationships[0];
    assert_eq!(rel.name, "parent_id_to_child_pid", "auto-named per ADR-0013");
    assert_eq!(rel.other_table, "parent");
    assert_eq!(rel.local_columns, vec!["pid".to_string()]);

-    let parent = r.block_on(db.describe_table("parent".to_string(), None)).expect("describe parent");
+    let parent = r.block_on(db.describe_table("parent".to_string())).expect("describe parent");
    assert_eq!(parent.inbound_relationships.len(), 1, "parent is referenced by child");
 }

@@ -954,7 +954,7 @@ fn explicit_constraint_name_is_used() {
        Some("create table child (id serial primary key, pid int, constraint child_to_parent foreign key (pid) references parent(id))".to_string()),
    ))
    .expect("create child with named FK");
-    let child = r.block_on(db.describe_table("child".to_string(), None)).expect("describe");
+    let child = r.block_on(db.describe_table("child".to_string())).expect("describe");
    assert_eq!(child.outbound_relationships[0].name, "child_to_parent");
 }

@@ -974,7 +974,7 @@ fn bare_references_resolves_to_parent_single_column_pk() {
        Some("create table child (id serial primary key, pid int references parent)".to_string()),
    ))
    .expect("create child with bare REFERENCES");
-    let child = r.block_on(db.describe_table("child".to_string(), None)).expect("describe");
+    let child = r.block_on(db.describe_table("child".to_string())).expect("describe");
    assert_eq!(child.outbound_relationships[0].other_columns, vec!["id".to_string()], "resolved to parent PK");
 }

@@ -1108,7 +1108,7 @@ fn create_table_with_fk_is_one_undo_step() {
    // parent (now un-referenced) can be described without a dangling rel.
    r.block_on(db.undo()).expect("undo").expect("a step was undone");
    assert!(!r.block_on(db.list_tables()).unwrap().contains(&"child".to_string()));
-    let parent = r.block_on(db.describe_table("parent".to_string(), None)).expect("describe parent");
+    let parent = r.block_on(db.describe_table("parent".to_string())).expect("describe parent");
    assert!(parent.inbound_relationships.is_empty(), "the relationship was undone with the table");
 }

@@ -1152,7 +1152,7 @@ fn foreign_key_on_delete_cascade_takes_effect() {
    ))
    .expect("delete parent");
    let child_rows = r
-        .block_on(db.query_data("child".to_string(), None, None, None))
+        .block_on(db.query_data("child".to_string(), None, None))
        .expect("query child");
    assert!(child_rows.rows.is_empty(), "ON DELETE CASCADE removed the child row");
 }
@@ -1232,7 +1232,7 @@ fn fk_survives_a_rebuild_triggering_column_add() {
        .expect("add column via rebuild");

    // The relationship still exists after the rebuild.
-    let child = r.block_on(db.describe_table("child".to_string(), None)).expect("describe");
+    let child = r.block_on(db.describe_table("child".to_string())).expect("describe");
    assert_eq!(child.outbound_relationships.len(), 1, "FK survived the column-add rebuild");
    // And the engine still enforces it (now and after a fresh rebuild).
    insert_parent_row(&db, &r);
@@ -1275,7 +1275,7 @@ fn fk_referential_actions_survive_rebuild() {
    ))
    .expect("create");
    r.block_on(db.rebuild_from_text(p.path().to_path_buf(), None)).expect("rebuild");
-    let child = r.block_on(db.describe_table("child".to_string(), None)).expect("describe");
+    let child = r.block_on(db.describe_table("child".to_string())).expect("describe");
    let rel = &child.outbound_relationships[0];
    assert_eq!(rel.on_delete, ReferentialAction::Cascade, "ON DELETE survived rebuild");
    assert_eq!(rel.on_update, ReferentialAction::SetNull, "ON UPDATE survived rebuild");
@@ -1299,7 +1299,7 @@ fn dropping_the_child_clears_the_fk_relationship() {
    .expect("create");
    r.block_on(db.drop_table("child".to_string(), Some("drop table child".to_string())))
        .expect("drop child");
-    let parent = r.block_on(db.describe_table("parent".to_string(), None)).expect("describe parent");
+    let parent = r.block_on(db.describe_table("parent".to_string())).expect("describe parent");
    assert!(parent.inbound_relationships.is_empty(), "dropping the child cleared the relationship");
 }

@@ -1341,7 +1341,7 @@ fn bare_self_reference_resolves_to_own_pk() {
        Some("create table emp (id int primary key, mgr int references emp)".to_string()),
    ))
    .expect("create self-referential emp with a bare reference");
-    let emp = r.block_on(db.describe_table("emp".to_string(), None)).expect("describe");
+    let emp = r.block_on(db.describe_table("emp".to_string())).expect("describe");
    assert_eq!(emp.outbound_relationships[0].other_columns, vec!["id".to_string()], "bare self-ref resolved to own PK");
    // Enforced: a non-existent manager is rejected.
    r.block_on(db.insert(
@@ -154,7 +154,7 @@ fn delete_without_where_runs_across_all_rows() {
    let csv = read_csv(&project, "t").unwrap_or_default();
    assert!(!csv.contains('a') && !csv.contains('b') && !csv.contains('c'), "no rows left: {csv:?}");
    let remaining = rt
-        .block_on(db.query_data("t".to_string(), None, None, None))
+        .block_on(db.query_data("t".to_string(), None, None))
        .expect("query t");
    assert!(remaining.rows.is_empty(), "table empty after unfiltered delete");
 }
@@ -302,8 +302,8 @@ fn cascade_to_two_children_reports_both() {
    assert_eq!(by_child.get("Orders"), Some(&2), "two orders cascaded");
    assert_eq!(by_child.get("Reviews"), Some(&1), "one review cascaded");
    // Both child CSVs re-persisted to the post-cascade (empty) state.
-    let orders = rt.block_on(db.query_data("Orders".to_string(), None, None, None)).unwrap();
-    let reviews = rt.block_on(db.query_data("Reviews".to_string(), None, None, None)).unwrap();
+    let orders = rt.block_on(db.query_data("Orders".to_string(), None, None)).unwrap();
+    let reviews = rt.block_on(db.query_data("Reviews".to_string(), None, None)).unwrap();
    assert!(orders.rows.is_empty() && reviews.rows.is_empty(), "both children emptied");
    let _ = &project;
 }
@@ -361,7 +361,7 @@ fn delete_violating_fk_fails_and_persists_nothing() {
    let result = run_delete(&db, &rt, input);
    assert!(result.is_err(), "delete of a referenced parent must be rejected");
    // Rolled back: Alice survives.
-    let customers = rt.block_on(db.query_data("Customers".to_string(), None, None, None)).unwrap();
+    let customers = rt.block_on(db.query_data("Customers".to_string(), None, None)).unwrap();
    assert_eq!(customers.rows.len(), 1, "parent row preserved after rejected delete");
    // No history line for the failed statement (written only on success).
    let history = std::fs::read_to_string(project.path().join("history.log")).unwrap_or_default();
@@ -149,7 +149,7 @@ fn seed(db: &Database, rt: &tokio::runtime::Runtime, sql: &str) {
 }

 fn query(db: &Database, rt: &tokio::runtime::Runtime, table: &str) -> Vec<Vec<Option<String>>> {
-    rt.block_on(db.query_data(table.to_string(), None, None, None))
+    rt.block_on(db.query_data(table.to_string(), None, None))
        .unwrap_or_else(|e| panic!("query_data {table}: {e:?}"))
        .rows
 }
@@ -55,7 +55,7 @@ fn make_t_with_index(db: &Database, r: &tokio::runtime::Runtime) -> String {
 }

 fn index_names(db: &Database, r: &tokio::runtime::Runtime) -> Vec<String> {
-    r.block_on(db.describe_table("T".to_string(), None))
+    r.block_on(db.describe_table("T".to_string()))
        .expect("describe")
        .indexes
        .into_iter()
@@ -150,7 +150,7 @@ fn drop_table_is_one_undo_step_and_restores_data() {
    assert!(r.block_on(db.undo()).expect("undo").is_some(), "the drop was one undo step");
    assert!(r.block_on(db.list_tables()).unwrap().contains(&"T".to_string()));
    let data = r
-        .block_on(db.query_data("T".to_string(), None, None, None))
+        .block_on(db.query_data("T".to_string(), None, None))
        .expect("query");
    assert_eq!(data.rows.len(), 1, "the dropped row was restored by undo");
 }
@@ -215,7 +215,7 @@ fn decimal_aggregation_display_trims_ieee754_noise() {

    // The reported case: the aggregate no longer leaks float noise.
    let agg = rt
-        .block_on(db.run_select("select sum(price * qty) from Products".to_string(), None))
+        .block_on(db.run_select("select sum(price * qty) from Products".to_string()))
        .expect("aggregate select");
    assert_eq!(
        agg.rows[0][0].as_deref(),
@@ -226,7 +226,7 @@ fn decimal_aggregation_display_trims_ieee754_noise() {
    // Raw decimal column is still exact — TEXT storage preserves
    // the input string verbatim, including the trailing zero.
    let raw = rt
-        .block_on(db.run_select("select price from Products".to_string(), None))
+        .block_on(db.run_select("select price from Products".to_string()))
        .expect("raw decimal select");
    let prices: Vec<&str> = raw.rows.iter().map(|r| r[0].as_deref().unwrap()).collect();
    assert_eq!(
@@ -240,10 +240,7 @@ fn decimal_aggregation_display_trims_ieee754_noise() {
 fn database_run_select_constant_returns_a_single_row() {
    let (_p, db, _dir) = open_project_db();
    let data = rt()
-        .block_on(db.run_select(
-            "select 1".to_string(),
-            Some("select 1".to_string()),
-        ))
+        .block_on(db.run_select("select 1".to_string()))
        .expect("`select 1` runs clean");
    assert_eq!(data.rows.len(), 1, "one result row");
    assert_eq!(data.rows[0].len(), 1, "one column");
@@ -288,7 +285,7 @@ fn database_run_select_from_user_table_returns_inserted_rows() {
        .expect("insert row");
    });
    let data = rt
-        .block_on(db.run_select("select Name from T".to_string(), None))
+        .block_on(db.run_select("select Name from T".to_string()))
        .expect("SELECT runs");
    assert_eq!(data.rows.len(), 1);
    assert_eq!(data.rows[0][0].as_deref(), Some("Ada"));
@@ -336,7 +333,7 @@ fn database_run_select_recovers_bool_column_type() {
        .expect("insert row");
    });
    let data = rt
-        .block_on(db.run_select("select Active from Products".to_string(), None))
+        .block_on(db.run_select("select Active from Products".to_string()))
        .expect("SELECT runs");
    assert_eq!(data.rows.len(), 2);
    assert_eq!(data.column_types, vec![Some(Type::Bool)]);
@@ -374,7 +371,7 @@ fn database_run_select_recovers_text_type_through_alias() {
    // playground type is recovered.
    let data = rt
        .block_on(
-            db.run_select("select Name as n from Users".to_string(), None),
+            db.run_select("select Name as n from Users".to_string()),
        )
        .expect("SELECT runs");
    assert_eq!(data.columns, vec!["n".to_string()]);
@@ -402,7 +399,7 @@ fn database_run_select_computed_expression_stays_typeless() {
            .expect("insert");
    });
    let data = rt
-        .block_on(db.run_select("select Score + 1 from T".to_string(), None))
+        .block_on(db.run_select("select Score + 1 from T".to_string()))
        .expect("SELECT runs");
    assert_eq!(data.column_types, vec![None]);
 }
@@ -439,7 +436,6 @@ fn engine_aggregate_in_where_routes_through_catalog() {
    let err = rt
        .block_on(db.run_select(
            "select id from T where count(score) > 0".to_string(),
-            None,
        ))
        .expect_err("engine should reject aggregate in WHERE");
    let DbError::Sqlite { .. } = &err else {
@@ -512,7 +508,6 @@ fn engine_group_by_missing_routes_through_catalog() {
    let _ = rt
        .block_on(db.run_select(
            "select category, count(*) from T group by category".to_string(),
-            None,
        ))
        .expect("benign GROUP BY query runs");
    // Direct unit test on the matcher: ensure a message that
@@ -574,7 +569,6 @@ fn engine_scalar_subquery_too_many_rows_routes_through_catalog() {
    let _ = rt
        .block_on(db.run_select(
            "select (select v from T) from T".to_string(),
-            None,
        ))
        .expect("benign scalar subquery query runs");
    let synthetic = DbError::Sqlite {
@@ -624,13 +618,13 @@ fn database_run_select_type_recovery_works_on_empty_table() {
    });
    // No INSERT — the table is empty.
    let data_text = rt
-        .block_on(db.run_select("select col_text from Empty".to_string(), None))
+        .block_on(db.run_select("select col_text from Empty".to_string()))
        .expect("SELECT runs even on empty table");
    assert!(data_text.rows.is_empty());
    assert_eq!(data_text.column_types, vec![Some(Type::Text)]);

    let data_blob = rt
-        .block_on(db.run_select("select col_blob from Empty".to_string(), None))
+        .block_on(db.run_select("select col_blob from Empty".to_string()))
        .expect("SELECT runs even on empty table");
    assert!(data_blob.rows.is_empty());
    assert_eq!(
@@ -723,7 +717,7 @@ fn database_run_select_recovers_all_ten_playground_types() {
    for (col, expected_type) in cases {
        let sql = format!("select {col} from AllTypes");
        let data = rt
-            .block_on(db.run_select(sql.clone(), None))
+            .block_on(db.run_select(sql.clone()))
            .expect("SELECT runs");
        assert_eq!(
            data.column_types,
@@ -501,7 +501,7 @@ fn update_all_rows_flag_in_advanced_updates_every_row() {
        "the --all-rows update replays through the DSL fall-back; events: {events:?}"
    );
    let rows = rt
-        .block_on(db.query_data("t".to_string(), None, None, None))
+        .block_on(db.query_data("t".to_string(), None, None))
        .expect("query")
        .rows;
    assert_eq!(rows.len(), 2, "both rows present");
@@ -63,7 +63,7 @@ async fn insert_named(db: &Database, name: &str) {
 }

 async fn row_count(db: &Database) -> usize {
-    db.query_data("Customers".to_string(), None, None, None)
+    db.query_data("Customers".to_string(), None, None)
        .await
        .unwrap()
        .rows
@@ -306,7 +306,7 @@ async fn sql_delete(db: &Database, input: &str) {
 }

 async fn count_t(db: &Database) -> usize {
-    db.query_data("T".to_string(), None, None, None)
+    db.query_data("T".to_string(), None, None)
        .await
        .unwrap()
        .rows
@@ -378,7 +378,7 @@ fn undo_restores_db_and_csv_consistently() {
        // Both the database read model and the on-disk CSV are
        // restored — the (db, csv) pair stays consistent.
        assert_eq!(
-            db.query_data("T".to_string(), None, None, None)
+            db.query_data("T".to_string(), None, None)
                .await
                .unwrap()
                .rows
@@ -250,6 +250,7 @@ fn command_kind_label(cmd: &rdbms_playground::dsl::Command) -> String {
        App(app) => match app {
            AppCommand::Quit => "App(Quit)".into(),
            AppCommand::Help { .. } => "App(Help)".into(),
+            AppCommand::Hint => "App(Hint)".into(),
            AppCommand::Rebuild => "App(Rebuild)".into(),
            AppCommand::Save => "App(Save)".into(),
            AppCommand::SaveAs => "App(SaveAs)".into(),
Author	SHA1	Message	Date
claude@clouddev1	47a08166a4	merging ci branch build-ci-image / build (push) Successful in 10m58s Details ci / gate (push) Successful in 3m8s Details	2026-06-15 16:07:10 +00:00
claude@clouddev1	6429b56443	feat(hint): H2 Phase C batch 2 — DDL tier-3 hints (ADR-0053) Per-form hints for the schema-shaping commands: create table, create m:n, add column/index/constraint, drop table/column/relationship/ index/constraint, rename column, change column (add_relationship was the Phase-B exemplar). Examples verified against the canonical usage templates. hint_ids wired on CREATE/CREATE_M2N/DROP/RENAME/CHANGE; catalogue + keys.rs registered. +2 spot tests (incl. multi-form DROP disambiguation); 2491 pass / 1 ignored, clippy clean.	2026-06-15 16:05:41 +00:00
claude@clouddev1	4bdfce6250	feat(hint): H2 Phase C batch 1 — app-command tier-3 hints (ADR-0053) Per-form hints for the 14 app-lifecycle commands (quit/help/hint/ rebuild/save/new/load/export/import/mode/messages/undo/redo/copy), reference-leaning what/example with concept where it teaches (rebuild, mode, messages, undo, export, help). hint_ids wired, catalogue + keys.rs registered. +1 spot test; 2489 pass / 1 ignored, clippy clean.	2026-06-15 16:01:39 +00:00
claude@clouddev1	138e766817	Merge branch 'main' into ci ci / gate (push) Successful in 3m5s Details Bring main's latest (ADRs 0049-0053 + their features) onto the CI branch so the gate runs against current main before CI lands on main. Clean merge — ci and main touched disjoint files.	2026-06-15 16:01:09 +00:00
claude@clouddev1	aeb92f56a7	docs(ci): record macOS implementation in ADR-ci-003 (D1 complete) ci / gate (push) Successful in 3m23s Details macOS is no longer deferred — built natively on a Tart (Apple-Silicon) runner (real hardware → licensed SDK, no grey area). Amendment documents release-macos.yaml (dispatch-only, needs main), the libiconv de-nix + ad-hoc re-sign, the runner-label `:host` backend nuance, generation-based cache pruning, and D2-on-macOS (system libs only). All six D1 targets now produce artifacts. Updates the deferred list + index entry.	2026-06-15 15:56:38 +00:00
claude@clouddev1	4a5fd1b5c1	feat(hint): H2 Phase B — per-form keying + the three exemplars (ADR-0053) The first exemplar (`add 1:n relationship`) showed per-node keying is too coarse for multi-form commands, so revise the mechanism to per-form. - CommandNode `hint_id: Option<&str>` -> `hint_ids: &[&str]` (mirrors usage_ids); hint_key_for_input_in_mode reuses a factored-out pick_form_key (shared digit/m:n/suffix form disambiguation with usage_key_for_input_in_mode) - wire INSERT + ADD (all four forms) with hint_ids - author the three approved exemplars: hint.cmd.insert, hint.cmd.add_relationship, hint.err.foreign_key.child_side (what/example/concept) + keys.rs registration - revise ADR-0053 D3 to per-form; record clause-concept hints as a deferred extension (issue #37); update README + plan - +5 tests; 2488 pass / 1 ignored, clippy clean	2026-06-15 12:18:41 +00:00
claude@clouddev1	050b36391e	feat(hint): H2 Phase A — `hint` command + F1 keybinding skeleton (ADR-0053) The mechanism for the contextual hint, with tier-2 fallback; the tier-3 corpus lands in later phases. - new CommandNode `hint_id` field (all None for now) - AppCommand::Hint + HINT grammar node + REGISTRY + dispatch - F1 read-only overlay in handle_key (buffer/cursor/memo untouched) - note_hint* renderers; hint_id_for_input_in_mode (shared selection helper refactored out of usage_keys_for_input_in_mode) - last_error_hint_key + friendly::error_hint_class classifier - catalogue: help.app.hint / parse.usage.hint / hint.getting_started - +12 tests; 2483 pass / 1 ignored, clippy clean	2026-06-15 10:36:51 +00:00
claude@clouddev1	9868442889	docs(plan): H2 contextual `hint` implementation plan (ADR-0053) Phased build plan: mechanism skeleton with tier-2 fallback first (hint_id field, AppCommand::Hint, F1 read-only overlay, last_error_hint_key, note_hint* renderer), then catalogue + the three approved exemplars, then comprehensive content in batches, then polish. Reuses the existing command_for_entry_word / usage_keys_for_input_in_mode lookups for command identification. Test spine includes the comprehensiveness coverage test that gates "comprehensive for v1".	2026-06-14 22:18:59 +00:00
claude@clouddev1	309d2e0b3f	ci: release-macos workflow (dispatch); retire macOS smoke-test The macOS release leg: workflow_dispatch (tag input) on the Tart runner — test → build both *-apple-darwin targets → rewrite nix libiconv to /usr/lib + ad-hoc re-sign → upload binary + .sha256 to the tagged release (idempotent create-or-get) → prune the nix store by generation. Composed entirely of parts the smoke-test proved green, so the smoke-test is removed. Dispatch-only fits the intermittent runner and keeps the 4-target Linux/ Windows release independent. Becomes triggerable once CI is on the default branch (workflow_dispatch is default-branch-only in Gitea).	2026-06-14 22:18:02 +00:00
claude@clouddev1	e16ad50aa7	docs(adr): ADR-0053 — contextual `hint` command + F1 keybinding (H2) Settles the `hint` slot ADR-0003 left pending; closes the last open piece of A1. Two surfaces (F1 → live-input hint; `hint` command → last-error expansion), no topic arg, and a new tier-3 teaching corpus keyed on a new CommandNode `hint_id` so advanced-SQL forms get distinct mode-correct content. Comprehensive content for v1, authored exemplars-first. Refines ADR-0003; references ADR-0019/0021/0022/0049/ 0051. Files #36 for the parallel help-side gap.	2026-06-14 22:14:11 +00:00
claude@clouddev1	60dbb903cc	ci: macOS smoke-test — run tests + nix-store generation pruning macos-build-test / build (push) Successful in 2m59s Details ci / gate (push) Successful in 3m6s Details - Add `cargo test` before the darwin builds (gate is Linux-only; the macOS leg is test-then-build) — a full dry-run of release-macos bar the upload. - Add an `if: always()` prune step. The runner wipes the workspace each run, so cargo target/ never accumulates (no sweep). The persistent cache is the nix store: record the current toolchain in a persistent profile, keep the 2 newest generations (nix-env --delete-generations +2), reclaim the rest (nix-collect-garbage). Pairs with min-free/max-free in the runner nix.conf.	2026-06-14 22:07:48 +00:00
claude@clouddev1	9a126782f1	ci: de-nix macOS binary libiconv via install_name_tool + re-sign macos-build-test / build (push) Successful in 2m11s Details build-ci-image / build (push) Successful in 9m49s Details ci / gate (push) Successful in 2m50s Details libiconv is the only /nix/store dep the darwin stdenv bakes in (everything else is system frameworks + libSystem/libobjc). The smoke-test now rewrites that load path to /usr/lib/libiconv.2.dylib (ABI-compatible, present on every Mac), re-signs ad-hoc (install_name_tool breaks the sig; arm64 requires a valid one), then verifies no /nix/store paths remain, the signature is valid, and the native binary launches. Flake comment updated to reflect the propagated-libiconv reality.	2026-06-14 21:43:01 +00:00
claude@clouddev1	4d004f5847	ci: drop nix libiconv from darwin build (portable macOS binary) macos-build-test / build (push) Failing after 1m36s Details build-ci-image / build (push) Successful in 9m45s Details ci / gate (push) Successful in 2m59s Details The smoke-test caught the aarch64 binary linking a /nix/store libiconv.dylib — non-portable (won't exist on a user's Mac). The Apple SDK already provides a system libiconv stub, so removing pkgs.libiconv makes the linker resolve -liconv to /usr/lib instead. The smoke-test now fails if any /nix/store dylib is linked.	2026-06-14 21:36:08 +00:00
claude@clouddev1	d5fb47bcc8	ci: macOS build smoke-test + flake darwin support macos-build-test / build (push) Successful in 3m52s Details build-ci-image / build (push) Successful in 10m3s Details ci / gate (push) Successful in 2m52s Details Add the two *-apple-darwin targets to rust-toolchain.toml and apple-sdk + libiconv to the flake devShell (darwin only) so the nix toolchain links AppKit; make cargo-zigbuild/zig Linux-only (macOS builds natively). Repoint the throwaway macOS workflow to actually build both darwin targets through the flake on the Tart runner — the first real check of the macOS leg, which can't be verified locally. Delete once release-macos lands.	2026-06-14 21:28:41 +00:00
claude@clouddev1	0878c6df19	ci: target the macOS runner by label name `macos` (not `macos:host`) macos-probe / probe (push) Successful in 57s Details ci / gate (push) Successful in 2m46s Details In act_runner a label is `<name>:<backend>`; `:host` is the execution- backend schema (run on host, no container), not part of the label. The runner registered as `macos:host` therefore has the label `macos`, which is what runs-on must reference.	2026-06-14 21:21:13 +00:00
claude@clouddev1	52815f1a76	ci: trigger macos-probe on push (workflow_dispatch needs default branch) ci / gate (push) Successful in 2m48s Details macos-probe / probe (push) Has been cancelled Details Gitea only exposes workflow_dispatch for workflows on the default branch (main); our CI is on `ci`, so the manual-run button/API isn't available. Add a push trigger (filtered to the probe file) so we can drive the macOS runner test from the ci branch. workflow_dispatch kept for post-merge.	2026-06-14 21:18:25 +00:00
claude@clouddev1	2721bd8d04	ci: macOS (Tart) runner probe — throwaway diagnostic ci / gate (push) Successful in 3m1s Details Manual-dispatch probe on runs-on macos:host to confirm the runner picks up jobs and report arch / macOS version / Xcode SDK / toolchains (nix, rustup, cargo) / git+node, before wiring the macOS release leg. Delete once done.	2026-06-14 21:11:28 +00:00
claude@clouddev1	e8fa859ab9	refactor(db): unwind vestigial worker source plumbing (ADR-0052 follow-up) ADR-0052 moved success journaling out of the worker to the dispatch layer, leaving the `source` that handlers threaded purely for the worker's old history.log write dead. Remove it: - drop `_source` from finalize_persistence and do_rebuild_from_text - inline + delete the three read-only *_request wrappers - drop the now-unused `source` param from the ~30 forwarding worker handlers (leaf + composite), compiler-guided - remove the `source` field from the DescribeTable/QueryData/RunSelect requests and their DatabaseHandle methods (call sites updated) The only worker `source` left is the snapshot/undo label (snapshot_then / stage_pre_mutation / begin_batch). Purely mechanical, no behaviour change. 2471 pass / 0 fail / 1 ignored, clippy clean.	2026-06-14 13:47:49 +00:00
claude@clouddev1	5869eec4f4	docs(ci): ADR-ci-003 — cross-platform release builds (D1 matrix) Record the multi-platform build strategy as its own decision: cargo-zigbuild for the four non-macOS targets, the static/standalone posture per platform, the Windows synchronization stub, the test->build matrix workflow, and the macOS deferral with its licensing rationale (the public CI image can't carry the SDK). Shrinks the ci-001 amendment to a pointer; updates the index. Runtime-verified by the user: Linux x86_64 + Windows aarch64 run correctly.	2026-06-13 19:11:29 +00:00
claude@clouddev1	298475b326	ci: D1 release matrix over the four non-macOS targets build-ci-image / build (push) Successful in 9m56s Details ci / gate (push) Successful in 2m47s Details release / test (push) Successful in 2m18s Details release / build (aarch64-pc-windows-gnullvm) (push) Successful in 3m31s Details release / build (aarch64-unknown-linux-musl) (push) Successful in 3m52s Details release / build (x86_64-pc-windows-gnu) (push) Successful in 4m14s Details release / build (x86_64-unknown-linux-musl) (push) Successful in 3m25s Details release.yaml becomes test (once, host) -> build (matrix) over the four cargo-zigbuild targets; each matrix job uploads its binary + .sha256 to the shared release (idempotent create-or-get). Records the expansion in ADR-ci-001 (2026-06-13 amendment); macOS stays deferred.	2026-06-13 12:14:49 +00:00
claude@clouddev1	04ebd83f08	build: D1 cross-compile via cargo-zigbuild (4 non-macOS targets) Replace the single-target musl cc with cargo-zigbuild + zig in the flake devShell — one universal cross cc/linker (incl. rusqlite's bundled SQLite C) for all four non-macOS D1 targets, added to rust-toolchain.toml: x86_64/aarch64-unknown-linux-musl (static, D2) x86_64-pc-windows-gnu, aarch64-pc-windows-gnullvm (standalone .exe) Windows links -lsynchronization (std WaitOnAddress), which rust-overlay's toolchain and zig's mingw don't ship; the symbols are forwarded by kernel32, so an empty stub libsynchronization.a (ci/winstub/, wired via .cargo/config.toml for the windows targets only) satisfies the linker. Verified: all four build; linux static; windows valid PE32+.	2026-06-13 12:14:49 +00:00
claude@clouddev1	18d08642d7	ci: skip the gate for docs-only changes ci / gate (push) Successful in 2m31s Details Add paths-ignore (docs/, /*.md) to the gate's push + pull_request triggers so markdown/docs-only changes don't run a full clippy+test that can't change the outcome. Mixed code+docs pushes still gate (not all files are ignored); flake/toolchain changes are deliberately not ignored. Also refresh a stale ADR-0049 -> ADR-ci-002 comment reference.	2026-06-12 22:42:50 +00:00
claude@clouddev1	da8bfebc36	docs(ci): establish docs/ci/adr namespace (ci-001 pipeline, ci-002 flake) ci / gate (push) Successful in 2m33s Details Records the CI/release pipeline as ADR-ci-001 and relocates the nix-flake ADR from main's ADR-0049 to ADR-ci-002 (content unchanged, history note added). Both live in docs/ci/adr/ with a README index — a dated, ci-segmented namespace disjoint from main's integer ADR sequence, the same split the website subproject uses to avoid cross-branch number collisions. Drops the ADR-0049 entry from docs/adr/README. ci-001 covers the runner model, the baked nix CI image, the clippy+test gate, the static-musl release on tag, trigger hygiene, auth, and scope.	2026-06-12 22:38:34 +00:00
claude@clouddev1	89b9392c25	ci: release job — test before publish, pin bash, fix diagnostic release / release (push) Successful in 3m59s Details build-ci-image / build (push) Successful in 7m27s Details ci / gate (push) Successful in 2m27s Details - Run cargo test before the build so a tag never publishes untested code. - Pin shell: bash on the scripted steps; the runner defaults to dash, which rejected `set -o pipefail` and failed run 22's package step. - Swap `file` (absent in the slim image) for `ls -l`.	2026-06-12 22:11:24 +00:00
claude@clouddev1	bba24120f1	ci: scope gate + image-build to branch pushes (skip tags) Tag pushes ignore paths: filters, so a release tag spuriously rebuilt the unchanged CI image and re-ran the gate on a commit the branch push already gated. Add branches: ['**'] to both push triggers — tag pushes no longer fire them (release.yaml owns tags). Pushing commits + a tag together still gates the commits via the branch push.	2026-06-12 22:11:24 +00:00
claude@clouddev1	88145225cc	ci: release workflow — static binary to Gitea releases on tag build-ci-image / build (push) Has been cancelled Details ci / gate (push) Successful in 2m32s Details release / release (push) Failing after 3m2s Details On a v* tag, builds the x86_64-unknown-linux-musl binary in the CI image and publishes it (+ .sha256) to a Gitea release via the API and the auto GITEA_TOKEN. x86_64 Linux only for now; rest of the D1 matrix and D3 packaging layer on later. Correctness comes from the branch gate.	2026-06-12 21:43:23 +00:00
claude@clouddev1	8e3208528e	build: static musl release build capability rust-toolchain.toml gains the x86_64-unknown-linux-musl target; the flake devShell gains a musl cc (pkgsCross.musl64) + CC/linker env so a `cargo build --target …-musl` compiles rusqlite's bundled SQLite C and links fully static (D2: single static binary, no runtime deps). Cargo release profile strips symbols (13MB -> 10MB). Verified locally: the musl binary is static-pie, statically linked, stripped, runs standalone.	2026-06-12 21:43:23 +00:00
claude@clouddev1	9d8161218a	ci: gate workflow + CI-image build/push, drop probe build-ci-image / build (push) Successful in 6m18s Details ci / gate (push) Successful in 3m19s Details - build-ci-image.yaml: builds .gitea/ci-image/Dockerfile via DinD and pushes git.lazyeval.net/oli/rdbms-playground-ci:latest (REGISTRY_* secrets); triggers on image-input changes + manual dispatch. - ci.yaml: the gate — runs inside that image, clippy -D warnings + cargo test, on push/PR. fmt intentionally not gated (ADR-0049). Removes ci-probe.yaml; it answered the runner questions (jobs run in containers, host nix unreachable, custom container: works).	2026-06-12 21:08:04 +00:00
claude@clouddev1	dc63ed66f1	ci: nix CI toolchain image (node-slim base + warmed flake) Job-container image the gate runs in. node:22-bookworm-slim satisfies the act_runner contract (sleep/bash/node) far more cheaply than the catthehacker images; single-user nix installed on top (pre-create /nix + empty build-users-group so it installs as root in a container) with the flake's devShell pre-warmed — CI enters a ready 1.95.0 toolchain in ~1.4s. Verified by local build. ~5.5GB (rust toolchain closure); dep/ target caching is a noted follow-up.	2026-06-12 21:08:04 +00:00
claude@clouddev1	c7ac0c9877	ci: add throwaway runner-probe workflow ci-probe / host (push) Failing after 54s Details ci-probe / nix-container (push) Failing after 1m12s Details Diagnostic to determine how the ci-public runner executes jobs and where the nix toolchain is reachable (host vs default container vs a custom container:), so the real gate is built on facts. Delete once the gate lands.	2026-06-12 20:35:39 +00:00
claude@clouddev1	9189740028	build(nix): reproducible dev + build env via a flake (ADR-0049) Root flake with two outputs: devShells.default (pinned 1.95.0 toolchain via rust-toolchain.toml + rust-overlay, plus cargo-sweep) and packages.default (rustPlatform.buildRustPackage from the committed Cargo.lock; doCheck=false). flake.lock pins nixpkgs nixos-26.05 / rust-overlay / flake-utils. .envrc (use flake) for direnv parity. Single source of toolchain for dev and the upcoming CI, so they can't drift. Verified through the flake: nix build yields a working binary, clippy clean, 2424 tests pass / 0 fail / 1 intentional ignored doctest. First step toward requirements.md TT5 + D1/D2/D3.	2026-06-12 20:35:39 +00:00