ADR-0027: existing-cases sweep + docs (step F)

Sweep: input_verdict tests confirm the schema-existence check
fires across the identifier-taking commands — unknown table
on drop / show / add column, unknown column on drop column /
update — and that known references stay clean. The Step B
check is grammar-generic, so this is verification + coverage
rather than new code.

Docs: requirements.md S6 -> [x], baseline 1096; CLAUDE.md
deferred list reconciled (C5a and S6 are done — removed);
ADR-0026's as-built note updated (step 5 shipped via
ADR-0027); ADR-0027 gains an As-built notes section
recording the post-walk diagnostics realization, the
pre-rendered message, the timeout-based debounce, coarse
WARNING spans, and the deferred highlight/hint wiring.

docs/requirements.md

@@ -26,13 +26,14 @@ repo is pushed).
 
 ## Test baseline
 
-After ADR-0026 steps 1–4 (complex WHERE expressions):
-**1070 passing, 0 failing, 1 ignored** (`cargo test` — the
-one ignored test is a long-standing `` ```ignore `` doc-test
-in `src/friendly/mod.rs`). Clippy clean with the nursery lint
-group enabled. (Earlier reference points: 1039 after ADR-0025
-(indexes); 1006 after ADR-0024 + the handoff-14 cleanup; 449
-after B2/C2.)
+After ADR-0027 (input-validity indicator): **1096 passing,
+0 failing, 1 ignored** (`cargo test` — the one ignored test
+is a long-standing `` ```ignore `` doc-test in
+`src/friendly/mod.rs`). Clippy clean with the nursery lint
+group enabled. (Earlier reference points: 1079 after ADR-0026
+(complex WHERE expressions); 1039 after ADR-0025 (indexes);
+1006 after ADR-0024 + the handoff-14 cleanup; 449 after
+B2/C2.)
 
 ---
 
@@ -60,12 +61,18 @@ after B2/C2.)
   for inspecting hints about the current input or last error.
 - [ ] **S5** Mode label and distinct border style on the input
   field communicate the current input mode at all times.
-- [ ] **S6** Input-field validity indicator: a debounced
+- [x] **S6** Input-field validity indicator: a debounced
   `[ERR]` / `[WRN]` marker at the right edge of the input row,
   summarising — before submit — whether the current command
   would run. Backed by a walker diagnostics-severity model
   (ERROR / WARNING). Advisory only — never blocks submission.
-  Designed in ADR-0027; implementation pending.
+  *(ADR-0027: `Severity` / `Diagnostic` on `WalkResult`;
+  `input_verdict` combines the parse outcome, schema-existence
+  ERRORs — unknown table / column — and the ADR-0026 §7
+  expression WARNINGs — type mismatch, `= NULL`. The runtime
+  debounces the indicator's display ~1 s; the rightmost six
+  columns of the input row are reserved unconditionally. New
+  `warning` theme colour.)*
 
 ## Input field