docs: handoff 19 — ADR-0027 highlight/hint wiring finished

ADR-0027 gains a "Follow-up" section recording the completed
§2 highlight + hint wiring and precise per-literal WARNING
spans; the three stale As-built bullets point at it.
requirements.md test baseline → 1125 and the S6 entry notes
the completion + Amendment 1. handoff-19 records the run and
queues the two deferred manual-testing bugs (add 1:n
relationship completion/usage hint; --resume / last_project)
as the next session's first work.

docs/adr/0027-input-validity-indicator.md

@@ -273,23 +273,72 @@ choices and deviations from the sketch above:
   still blocks plainly. Any event resets the window (not
   only keystrokes) — a slight over-reset, harmless in
   practice.
-- **WARNING spans are coarse** — the whole WHERE clause. The
-  `Expr` AST carries no source spans, and the indicator
-  reads only severity. Precise per-literal spans (for a
-  future warning-highlight overlay) are a refinement.
-- **Highlight / hint integration beyond the indicator** —
-  §2 notes highlighting and the hint panel "read the
-  individual diagnostics". The indicator and the model
-  ship; routing diagnostic spans into the per-byte highlight
-  overlay, and diagnostic messages into the hint panel
-  beyond the existing parse-error path, is a follow-up (the
-  build order did not enumerate it as a step).
-- **Debounce timing is not unit-tested** — it is async
-  event-loop glue. `App::input_validity_verdict` (the pure
-  verdict) and the indicator rendering are covered;
+- **WARNING spans are per-literal.** Each `Operand` AST node
+  carries the byte span of the terminal it was built from, so
+  an expression WARNING is anchored to exactly the offending
+  literal. *(The initial ship used a coarse whole-WHERE-clause
+  span; made precise in the Follow-up section below.)*
+- **Highlight & hint wiring — complete.** §2's "highlighting
+  and the hint panel read the individual diagnostics" is
+  wired — see the Follow-up section below. *(The initial ship
+  had the indicator and the model only; the build order did
+  not enumerate the wiring as a step.)*
+- **Debounce decision logic is unit-tested** — it is the
+  `IndicatorDebounce` state machine in `runtime` (Follow-up
+  section). The `tokio::time::timeout` interaction itself
+  stays integration-level. The pure verdict
+  (`input_verdict` / `input_validity_verdict`) and the
+  indicator rendering were covered from the initial ship;
   `input_verdict` has a parse-outcome / schema-existence /
   expression-warning / existing-cases-sweep test set.
 
+## Follow-up — highlight & hint wiring, precise spans (2026-05-19)
+
+The As-built notes above left three items open; this pass
+closes them. §2's design — "the indicator is the summary;
+highlighting and the hint panel read the individual
+diagnostics for *where* and *why*" — is now fully realised.
+
+- **`Operand` carries a source span.** Each WHERE-expression
+  operand records the byte range of the terminal it was built
+  from. `Operand`'s `PartialEq` is hand-written to *ignore*
+  the span — it is editor metadata — so `Command` equality,
+  and the large `Expr` test corpus, stay whitespace- and
+  position-independent. Expression WARNINGs are now anchored
+  to exactly the offending literal, not the whole clause.
+- **`walker::input_diagnostics`** is the shared entry point
+  both UI layers read — the sibling of `input_verdict` that
+  returns the diagnostic set rather than its severity summary.
+- **Highlight overlay.** `render_input_runs` overlays the
+  schema-aware diagnostics on the input field: an unknown
+  table / column ERROR in the error colour, an expression
+  WARNING in `theme.warning`. The overlay is *global* — every
+  flagged token is coloured wherever it sits, not only under
+  the cursor, which is precisely the problem §Context
+  describes. The pre-existing cursor-local invalid-identifier
+  overlay is kept (it covers in-progress identifiers, which
+  produce no diagnostics); the two are additive and
+  idempotent. `overlay_span` recolours a token's whole byte
+  range (the older `overlay_error` hit only a single byte).
+- **Hint panel.** `ambient_hint` surfaces a diagnostic's
+  message. `input_diagnostics` is non-empty only for a
+  command that structurally parses — so a non-empty result
+  means "complete and submittable, but wrong or dubious". It
+  is checked early, ahead of slot hints and completions, so a
+  flawed-but-parsing command no longer gets the misleading
+  "Submit with Enter" prose. The diagnostic under the cursor
+  wins (the panel explains where the user is looking);
+  otherwise the most severe.
+- **Debounce.** The indicator-debounce decision logic moved
+  out of the event loop into the `IndicatorDebounce` state
+  machine, unit-tested for the keystroke / settle cycle.
+
+The one piece still integration-level: a PTY-tier test of the
+actual `tokio` debounce *timing* (as distinct from the
+now-tested decision logic) — consistent with the four-tier
+strategy (ADR-0008), where Tier 4 is wired only for the
+critical flows.
+
 ## Amendment 1 — `LIKE` on a numeric column (2026-05-19)
 
 §1 defined the WARNING set as exactly a type-mismatched