2g: advanced-mode highlight + engine.* wiring + matrix tests

Cross-cut verification matrix for ADR-0032 Phase 2 is now fully
populated with concrete test references — every row green. Filling
the matrix surfaced three real gaps that this commit closes.

1. Advanced-mode syntax highlighting (ADR-0030 §8 matrix row).
   The `ui.rs` Advanced branch routed through `plain_input_spans`,
   bypassing the highlight walker entirely. In production SQL
   keywords past the entry word rendered as plain identifiers.
   Fix: mode-aware variants of `highlight_runs`,
   `render_input_runs`, `lex_to_runs`, and `input_diagnostics`;
   the Advanced render path now uses the highlighted form with
   `Mode::Advanced`. `plain_input_spans` removed (unused).

2. Engine.* key wiring (ADR-0032 §11.4 / §13 matrix rows + handoff
   §3.3 follow-up). The four Phase-2 engine.* catalog entries
   were authored in 2d but never reached: `translate_generic`
   discarded the engine message and returned a vague catalog
   entry. Fix: pattern-match the engine message text for the four
   Phase-2 categories (aggregate misuse, group-by required,
   compound arity mismatch fallback, scalar-subquery cardinality)
   inside `translate_generic`, routing each to its engine-neutral
   catalog entry.

3. Matrix-coverage tests. Thirteen new tests covering the rows
   that had no explicit coverage:
   - 3 SQL keyword/operator/CASE highlight tests
   - 4 engine.* engine-message tests
   - 3 sql_expr column-completion tests (WHERE, HAVING)
   - 3 predicate-warning slot tests (CASE, ORDER BY, projection)
   - 1 all-10-playground-types recovery test (tests/sql_select.rs)

Plan document (docs/plans/20260520-adr-0032-phase-2.md) updated:
every (TBD) row in the cross-cut matrix replaced with a concrete
test file::function reference and a green status marker.

Test totals: 1428 → 1441 passing (+13 new). Clippy clean.

src/input_render.rs

@@ -67,28 +67,39 @@ pub fn render_input_runs(
     theme: &Theme,
     cache: &crate::completion::SchemaCache,
 ) -> Vec<StyledRun> {
-    let mut runs = lex_to_runs(input, theme);
-    // `render_input_runs` is invoked from `ui.rs` only when the
-    // effective mode is plain `Simple` (advanced rendering uses
-    // `plain_input_spans`), so the classification must use the
-    // simple-mode walker view (ADR-0030 §2): a SQL form here
-    // surfaces as a definite error overlay, consistent with the
-    // dispatch path's "this is SQL" hint on submit.
+    render_input_runs_in_mode(input, cursor_byte, theme, cache, Mode::Simple)
+}
+
+/// Mode-aware [`render_input_runs`] (ADR-0030 §8).
+///
+/// Advanced mode runs the highlight walker with `Mode::Advanced`
+/// so SQL keywords get matched and coloured, and the
+/// definite-error / schema-existence overlays use the
+/// advanced-mode parse view.
+#[must_use]
+pub fn render_input_runs_in_mode(
+    input: &str,
+    cursor_byte: usize,
+    theme: &Theme,
+    cache: &crate::completion::SchemaCache,
+    mode: Mode,
+) -> Vec<StyledRun> {
+    let mut runs = lex_to_runs_in_mode(input, theme, mode);
     if let InputState::DefiniteErrorAt(pos) =
-        classify_parse_result(parse_command_with_schema_in_mode(input, cache, Mode::Simple))
+        classify_parse_result(parse_command_with_schema_in_mode(input, cache, mode))
     {
         overlay_error(&mut runs, pos, theme);
     }
     if let Some(inv) = crate::completion::invalid_ident_at_cursor(input, cursor_byte, cache) {
         overlay_error(&mut runs, inv.range.0, theme);
     }
-    // Schema-aware diagnostics (ADR-0027 §2): an unknown table
-    // or column (ERROR), or a dubious comparison (WARNING), is
-    // overlaid wherever it sits in the input — not only under
-    // the cursor, so a problem the user has typed past stays
-    // visible. `input_diagnostics` is empty on a parse failure,
-    // so this never fights the definite-error overlay above.
-    for diag in walker::input_diagnostics(input, Some(cache)) {
+    // Schema-aware diagnostics (ADR-0027 §2): unknown table /
+    // column (ERROR), or a dubious comparison (WARNING), is
+    // overlaid wherever it sits — not only under the cursor —
+    // so a problem the user has typed past stays visible. The
+    // mode-aware walk picks up the SQL-specific diagnostics from
+    // ADR-0032 in advanced mode.
+    for diag in walker::input_diagnostics_in_mode(input, Some(cache), mode) {
         let colour = match diag.severity {
             walker::Severity::Error => theme.tok_error,
             walker::Severity::Warning => theme.warning,
@@ -503,15 +514,28 @@ fn overlay_span(runs: &mut [StyledRun], span: (usize, usize), colour: Color) {
 /// no cursor to show.
 #[must_use]
 pub fn lex_to_runs(input: &str, theme: &Theme) -> Vec<StyledRun> {
-    base_runs(input, theme)
+    lex_to_runs_in_mode(input, theme, Mode::Simple)
 }
 
-fn base_runs(input: &str, theme: &Theme) -> Vec<StyledRun> {
+/// Mode-aware [`lex_to_runs`]. Advanced mode runs the walker
+/// with `Mode::Advanced` so SQL keywords past the entry word
+/// match and get highlighted (ADR-0030 §8).
+#[must_use]
+pub fn lex_to_runs_in_mode(
+    input: &str,
+    theme: &Theme,
+    mode: Mode,
+) -> Vec<StyledRun> {
+    base_runs(input, theme, mode)
+}
+
+fn base_runs(input: &str, theme: &Theme, mode: Mode) -> Vec<StyledRun> {
     // Walker-driven highlighting (ADR-0024 §architecture, Phase F).
-    // `walker::highlight_runs` returns per-byte classes for every
-    // token shape in the source; whitespace gaps are not represented
-    // and we fill them with the default foreground colour below.
-    let classes = walker::highlight_runs(input);
+    // `walker::highlight_runs_in_mode` returns per-byte classes for
+    // every token shape in the source; whitespace gaps are not
+    // represented and we fill them with the default foreground
+    // colour below.
+    let classes = walker::highlight_runs_in_mode(input, mode);
     let mut runs = Vec::with_capacity(classes.len() * 2);
     let mut pos = 0;
     for class in classes {