feat(hint): H2 Phase C batch 4 — advanced-mode SQL tier-3 hints (ADR-0053)

Distinct SQL-syntax hints for the 11 advanced-mode forms: sql create
table / alter table / create index / drop index / drop table / insert /
update / delete, select, with, explain. hint_ids wired on all 11 nodes.

Hardened hint_key_for_input_in_mode for shared entry words: a bare
multi-form entry word defers to tier-2; when the second token isn't a
form word (insert into / update … set), it falls back to the
mode-primary key — so advanced mode resolves to the SQL form and simple
mode to the DSL form. catalogue + keys.rs registered. +2 spot tests +
grammar mode-disambiguation asserts; 2495 pass / 1 ignored, clippy clean.

src/dsl/grammar/mod.rs

@@ -616,10 +616,13 @@ pub fn usage_keys_for_input_in_mode(
 /// form has no tier-3 block yet (the caller falls back to tier-2).
 #[must_use]
 pub fn hint_key_for_input_in_mode(source: &str, mode: crate::mode::Mode) -> Option<&'static str> {
+    use crate::dsl::walker::lex_helpers::{consume_ident, skip_whitespace};
     let nodes = selected_nodes_for_input_in_mode(source, mode);
     if nodes.is_empty() {
         return None;
     }
+    // Mode-ordered union (advanced-primary first in advanced mode), so a
+    // shared entry word resolves to the surface the user is in.
     let mut keys: Vec<&'static str> = Vec::new();
     for (_, node, _) in &nodes {
         for k in node.hint_ids {
@@ -628,7 +631,25 @@ pub fn hint_key_for_input_in_mode(source: &str, mode: crate::mode::Mode) -> Opti
             }
         }
     }
-    pick_form_key(source, &keys)
+    if keys.is_empty() {
+        return None;
+    }
+    if keys.len() == 1 {
+        return Some(keys[0]);
+    }
+    // A bare multi-form entry word (no form word yet — `add`⏎) has no
+    // chosen form: defer to tier-2, which lists the choices.
+    let start = skip_whitespace(source, 0);
+    if let Some((_, entry_end)) = consume_ident(source, start)
+        && skip_whitespace(source, entry_end) >= source.len()
+    {
+        return None;
+    }
+    // A form word picks the form (`drop column` → `drop_column`); when
+    // the second token isn't a form word (`insert into …`, `update …
+    // set`), fall back to the mode-primary key — in advanced mode the
+    // SQL form, in simple mode the DSL form.
+    pick_form_key(source, &keys).or_else(|| keys.first().copied())
 }
 
 /// Shared mode-aware command-form selection for the entry word at the
@@ -922,6 +943,22 @@ mod hint_key_tests {
             hint_key_for_input_in_mode("drop table T", Mode::Simple),
             Some("drop_table")
         );
+        // Mode picks the surface for a shared entry word whose second
+        // token isn't a form word: SQL form in advanced, DSL in simple.
+        assert_eq!(
+            hint_key_for_input_in_mode("insert into T values (1)", Mode::Advanced),
+            Some("sql_insert")
+        );
+        assert_eq!(
+            hint_key_for_input_in_mode("insert into T values (1)", Mode::Simple),
+            Some("insert")
+        );
+        // `create table` shares a form word — advanced-first ordering
+        // resolves it to the SQL form in advanced mode.
+        assert_eq!(
+            hint_key_for_input_in_mode("create table T (id int)", Mode::Advanced),
+            Some("sql_create_table")
+        );
         // Unknown entry word → None (tier-2 fallback).
         assert_eq!(hint_key_for_input_in_mode("zzz", Mode::Simple), None);
     }