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/dsl/walker/highlight.rs

@@ -31,13 +31,28 @@ use crate::dsl::walker::outcome::{ByteClass, WalkBound};
 
 /// Produce the per-byte highlight classes for `source`.
 ///
-/// On a successful walk this is exactly the walker's recorded
-/// classes. On partial / unmatched input the byte-shape scanner
-/// fills the gap so the renderer keeps colouring through trailing
-/// tokens and unknown-command inputs.
+/// Defaults to `Mode::Simple`. Callers in advanced-mode UIs
+/// should use [`highlight_runs_in_mode`] so SQL keywords get
+/// matched and highlighted past the entry word (the simple-mode
+/// gate at the dispatcher truncates the walker on advanced-only
+/// commands, ADR-0030 §2).
 #[must_use]
 pub fn highlight_runs(source: &str) -> Vec<ByteClass> {
+    highlight_runs_in_mode(source, crate::mode::Mode::Simple)
+}
+
+/// Mode-aware [`highlight_runs`] (ADR-0032 §10.6 follow-up).
+///
+/// In `Mode::Advanced` the walker matches every Phase-2 SQL
+/// token, producing the keyword classes the renderer needs to
+/// colour `select` / `from` / `where` / `union` / `case` / etc.
+#[must_use]
+pub fn highlight_runs_in_mode(
+    source: &str,
+    mode: crate::mode::Mode,
+) -> Vec<ByteClass> {
     let mut ctx = WalkContext::new();
+    ctx.mode = mode;
     let (result, _cmd) = super::walk(source, WalkBound::EndOfInput, &mut ctx);
     let mut classes: Vec<ByteClass> = result
         .map(|r| r.per_byte_class)
@@ -316,4 +331,70 @@ mod tests {
         assert_eq!(runs[0].2, HighlightClass::String);
         assert_eq!(runs[0].1, "'café'".len());
     }
+
+    // ---- ADR-0030 §8 / ADR-0032 — SQL keyword highlighting ----
+
+    fn run_advanced(input: &str) -> Vec<(usize, usize, HighlightClass)> {
+        highlight_runs_in_mode(input, crate::mode::Mode::Advanced)
+            .into_iter()
+            .map(|c| (c.start, c.end, c.class))
+            .collect()
+    }
+
+    #[test]
+    fn sql_select_keywords_classified() {
+        // ADR-0030 §8 — `select` / `from` get keyword class in
+        // Advanced mode (Simple mode gates SELECT out at the
+        // dispatcher, so only the entry word would highlight).
+        let runs = run_advanced("select * from t");
+        assert!(
+            runs.iter().any(|(s, e, c)| {
+                *c == HighlightClass::Keyword && (*s, *e) == (0, 6)
+            }),
+            "expected `select` keyword span 0..6; got {runs:?}",
+        );
+        assert!(
+            runs.iter().any(|(s, e, c)| {
+                *c == HighlightClass::Keyword && (*s, *e) == (9, 13)
+            }),
+            "expected `from` keyword span 9..13; got {runs:?}",
+        );
+    }
+
+    #[test]
+    fn sql_expression_operators_classified_as_keywords() {
+        // ADR-0031 §5: LIKE / BETWEEN / IN / IS / AND / OR / NOT
+        // are part of the predicate ladder. Walker matches them
+        // as Word nodes; highlight class = Keyword.
+        let input = "select * from t where a like 'x' and b between 1 and 5";
+        let runs = run_advanced(input);
+        let keywords: Vec<&str> = runs
+            .iter()
+            .filter(|(_, _, c)| *c == HighlightClass::Keyword)
+            .map(|(s, e, _)| &input[*s..*e])
+            .collect();
+        assert!(keywords.contains(&"like"), "no `like`; got {keywords:?}");
+        assert!(keywords.contains(&"and"), "no `and`; got {keywords:?}");
+        assert!(
+            keywords.contains(&"between"),
+            "no `between`; got {keywords:?}",
+        );
+    }
+
+    #[test]
+    fn sql_case_expression_keywords_classified() {
+        let input = "select case when a = 1 then 'one' else 'other' end from t";
+        let runs = run_advanced(input);
+        let keywords: Vec<&str> = runs
+            .iter()
+            .filter(|(_, _, c)| *c == HighlightClass::Keyword)
+            .map(|(s, e, _)| &input[*s..*e])
+            .collect();
+        for kw in ["case", "when", "then", "else", "end"] {
+            assert!(
+                keywords.contains(&kw),
+                "missing `{kw}` keyword; got {keywords:?}",
+            );
+        }
+    }
 }