docs: handoff 18 — record the post-ADR-0027 manual-testing pass

The multi-form usage-template fix (151ed08) and the reviewed
`add index` syntax decision (kept as-is), so the next agent
does not re-flag a settled question.

docs/handoff/20260519-handoff-18.md

@@ -18,12 +18,13 @@ run. `S6` and `C5a` are both satisfied; nothing from ADRs
 
 ## State at handoff
 
-**Branch:** `main`. Working tree clean. **11 commits** since
+**Branch:** `main`. Working tree clean. **12 commits** since
 handoff-16 (`ac41938`), all local — push asynchronously, not
 blocking. handoff-17 (`dfd3c51`) is mid-chain; it documents
 the ADR-0026 landing and is superseded by this file.
 
 ```
+151ed08 hint: show the matching usage template for multi-form commands
 a326849 ADR-0027: existing-cases sweep + docs (step F)
 9e10997 runtime: debounce the validity indicator (ADR-0027 step E)
 1a9d950 ui: validity indicator rendering + warning theme colour (ADR-0027 step D)
@@ -37,7 +38,7 @@ f75f71b WHERE expressions: wire into update/delete/show data + SQL gen (ADR-0026
 f0b2043 walker: add Subgrammar node + recursion-depth cap (ADR-0026 step 1)
 ```
 
-**Tests:** **1099 passing, 0 failing, 1 ignored** (`cargo
+**Tests:** **1100 passing, 0 failing, 1 ignored** (`cargo
 test` — up from 1039 at handoff-16). The ignored test is the
 long-standing `` ```ignore `` doc-test in
 `src/friendly/mod.rs`. Typing-surface matrix: **161 cells**.
@@ -91,6 +92,38 @@ Six steps, one commit each (`e22f933`..`a326849`):
 - **F — sweep + docs.** `input_verdict` tests confirm the
   schema check fires across the identifier-taking commands.
 
+## §2a. Post-ADR-0027 — a manual-testing pass
+
+After ADR-0027 landed, a round of manual testing surfaced
+three things; all are resolved.
+
+- **Bug, fixed (`151ed08`).** A parse error in `add index …`
+  showed the `add column` usage. `add` / `drop` are
+  multi-form commands and both the ambient hint and the
+  submit-time usage block picked the *first* form
+  unconditionally. New `grammar::usage_key_for_input`
+  disambiguates by the form word after the entry keyword;
+  the hint shows the committed form, `render_usage_block`
+  too (bare `add` / `drop` still shows the whole family).
+- **`add index` syntax — reviewed, deliberately kept.** The
+  inconsistency is real: `add column [to] [table] <T>: <col>
+  (<type>)` vs `add index [as <name>] on <T> (<cols>)`. It
+  was weighed and **left as-is** — `add index … on <T>
+  (<cols>)` is intentionally SQL-idiomatic
+  (`CREATE INDEX … ON t (cols)`), the colon shape was built
+  for "one column *with a type*" and an index has neither.
+  A future agent should **not** re-flag this as a bug; if
+  the owner later wants the entity-command separators
+  unified, that is a deliberate ADR-0025 amendment / design
+  pass, not a drive-by fix.
+- **No index parameters / no `unique` — by design.** ADR-0025
+  scoped `add index` to plain non-unique indexes; there is
+  no `unique`-index syntax and no constraint syntax at all
+  (`NOT NULL` / `UNIQUE` / `CHECK` / `DEFAULT` are the
+  pending `C3`). ADR-0018's `unique` handling only
+  *detects + displays* an existing constraint — nothing
+  creates one. Not a gap in the help; the help is accurate.
+
 ## §3. Architectural delta (vs. handoff-17)
 
 ### Diagnostics
@@ -171,7 +204,7 @@ Prioritisation is a user product decision — ask.
    especially its "As-built notes" (post-walk diagnostics,
    the pre-rendered message, the `timeout` debounce, coarse
    spans, the deferred highlight/hint wiring).
-4. **Run `cargo test`** — 1099 passing, 0 failing, 1 ignored.
+4. **Run `cargo test`** — 1100 passing, 0 failing, 1 ignored.
 5. **Run `cargo clippy --all-targets -- -D warnings`** — clean.
 6. **Pick the next work from §5** — ADR-0028 is the natural
    pick; prioritisation is a user decision, so ask.