# Session handoff — 2026-05-19 (23) Twenty-third handover. This session **finished ADR-0029** — column constraints (`NOT NULL` / `UNIQUE` / `CHECK` / `DEFAULT`). Commits 5–6, planned in full in handoff-22 §4, are implemented, tested and committed. **ADR-0029 is complete**; requirement `C3` (schema constraints) is now ticked in `docs/requirements.md`. ## §1. State at handoff **Branch:** `main`. Working tree clean (after this docs commit). **3 commits** since handoff-22 (`102dff0`) — two feature commits plus this handoff — all local; push asynchronously, not blocking. ``` docs: handoff 23 — ADR-0029 complete; tick C3 5e97f6a constraints: CHECK-violation friendly error + typing-surface matrix (ADR-0029 §10) abce118 constraints: `add constraint` / `drop constraint` on existing columns (ADR-0029 §2.2) ``` **Tests:** **1240 passing, 0 failing, 1 ignored** (`cargo test`). The ignored test is the long-standing `` ```ignore `` doc-test in `src/friendly/mod.rs`. Typing-surface matrix: **188 cells** (was 174 — +14 for the constraint grammar). **Clippy:** clean (`cargo clippy --all-targets -- -D warnings`, nursery group). ## §2. What ADR-0029 delivered (full picture) Commits 1–4 (handoff-22) landed the constraint *suffix* — `not null` / `unique` / `default ` / `check ()` after a column's `(type)` group on `create table` and `add column`, the db-layer DDL/round-trip, and the §6 `add column` routing. This session added the rest: **Commit 5 (`abce118`) — `add constraint` / `drop constraint`.** The §2.2 surface for modifying an *existing* column's constraints: ``` add constraint not null to . add constraint unique to . add constraint default to . add constraint check ( ) to . drop constraint (not null | unique | default | check) from . ``` - **Grammar** (`src/dsl/grammar/ddl.rs`): `ADD_CONSTRAINT` / `DROP_CONSTRAINT` join the `add` / `drop` `Choice`s, discriminated by the `constraint` form word. `add constraint` reuses the §2.1 `COLUMN_CONSTRAINT` Choice; `drop constraint` uses a payload-free `DROP_CONSTRAINT_KIND` Choice. `CONSTRAINT_TARGET` is the dotted `.` (`table_name` / `column_name` roles — distinct from the CHECK expression's `expr_column`, so the target column never collides with an expression column). - **AST** (`src/dsl/command.rs`): `Command::AddConstraint` / `DropConstraint`; `Constraint` (payload-carrying) / `ConstraintKind` (payload-free) enums. - **Worker** (`src/db.rs`): `do_add_constraint` / `do_drop_constraint` apply the change through the rebuild-table primitive. `do_add_constraint` runs the §5 **dry-run first** — `dry_run_not_null` / `dry_run_unique` / `dry_run_check` scan the existing rows and, on a violation, refuse *before any write* with a pretty-printed table of offending rows (the `db.diagnostic.add_*_summary` catalog keys + `render_diagnostic_table`, mirroring `do_change_column_type`). §9 redundant-on-PK declarations and §6 `default` on a `serial` / `shortid` column are friendly refusals. - Both return `TableDescription` → `CommandOutcome::Schema` → the existing auto-show path (no new `AppEvent`). **Commit 6 (`5e97f6a`) — CHECK friendly error + matrix.** - **CHECK-violation friendly error (ADR §10).** The friendly layer already had a `translate_check` + `error.check.*` catalog entries (placeholder from an earlier session), but nothing filled the column in. `enrich_dsl_failure` (`src/runtime.rs`) gained a CHECK branch: `enrich_check_violation` reads the column from the engine's `CHECK constraint failed: ` message, then resolves the table, the offending value, and the column's compiled `CHECK` expression. `FailureContext` / `TranslateContext` carry a new `check_rule` field; `translate_check` renders "the value `` breaks the rule ``" when the rule is known, falling back to the plain hint otherwise. - **Typing-surface matrix.** New `tests/typing_surface/ constraints.rs` — 14 cells covering the create-table / add-column constraint suffix and `add` / `drop constraint`. ## §3. Decisions / deviations this session 1. **`schema_to_ddl` UNIQUE bug fixed** (`abce118`). It suppressed `UNIQUE` for *every* PK column. A *compound*-PK member is **not** individually unique, so an explicit `UNIQUE` on it must survive the rebuild. The condition is now "suppress only for a *single-column* PK". Caught by the `add_constraint_unique_on_compound_pk_member_is_allowed` test. Pre-existing latent bug. 2. **"Nothing to drop" is a friendly refusal** (`abce118`) — `drop constraint` on a constraint the column never carried refuses ("`T.col` has no UNIQUE constraint to drop") instead of a silent no-op rebuild. This was *not* spelled out in handoff-22 §4; it is consistent with ADR-0029 §9's "clarity over permissiveness" and was an autonomous call — flagged here and accepted by the user at commit time. 3. **CHECK friendly error went full ADR §10** (`5e97f6a`) — the user chose, when asked, to surface the rule + offending value rather than the minimal handoff-§4 scope. ADR §10's prose said "DSL-form expression"; deviation §7 had removed the DSL-text form, so §10 was updated to say the rule is shown in its **compiled-SQL form** — consistent with §7/§8. ## §4. Key reusable pieces (this session) - `src/db.rs`: `do_add_constraint` / `do_drop_constraint`; `read_constraint_dry_run_rows` + `dry_run_not_null` / `dry_run_unique` / `dry_run_check`; `render_constraint_ dry_run` and the `dry_run_id_*` helpers; `value_to_default_ sql` (factored out of `default_sql_literal`). `DryRunRow` type alias. - `src/runtime.rs`: `enrich_check_violation`. - `src/friendly/`: `FailureContext.check_rule` / `TranslateContext.check_rule`; `error.check.*.hint_with_rule` catalog keys. - `Operation::AddConstraint` / `DropConstraint` in `src/friendly/translate.rs`. ## §5. What's next ADR-0029 closes requirement `C3`. No feature is in flight. Open clusters (prioritisation is a **user decision — ask**): - Snapshot / undo / replay `U`-series (designed in ADR-0006, not yet implemented). - m:n convenience `C4`; modify-relationship `C3a` (drop+add covers it today). - Project storage Iter 5–6: `export` / `import`, `--resume`, persistent input history, migration-framework scaffold. - SQL handling in advanced mode (`sqlparser-rs`, its own ADR). - Friendly-error layer `H1` (the remaining SQL→English sweep); strong syntax-help in parse errors `H1a`. - Session-log / Markdown export `V4`; ER diagram export `V3`. - CI workflow `TT5`; readline shortcuts `I1b`; multi-line input `I1`; Tab completion polish `I3`. ## §6. How to take over 1. **Read this file**, then `CLAUDE.md` (working-style rules), then `docs/requirements.md` (per-item progress — `C3` now ticked). 2. **Run `cargo test`** — 1240 passing, 0 failing, 1 ignored. 3. **Run `cargo clippy --all-targets -- -D warnings`** — clean. 4. Pick the next cluster *with the user* — §5 has no default. ### Note on the typing-surface matrix `tests/typing_surface/` is **188 cells**. The matrix-snapshot discipline stands: a failing cell with *correct* new behaviour → update its snapshot; with *wrong* behaviour → the cell earned its keep. `cargo insta` is not installed — regenerate with `INSTA_UPDATE=always cargo test --test typing_surface_matrix ` and review the written `.snap` files before committing.