Hint: pedagogical Form-A pointer at Form B's first value slot

Handoff-12 §2.2: Form B `insert into T values (…)` silently skips
auto-generated columns from the value list, so a user who wants to
set a serial/shortid column explicitly could only discover Form A by
reading help. Now the hint at the first Form B value slot appends a
note naming the skipped column(s) and pointing at the explicit-column
form.

hint_resolution_at_input derives the skipped columns from the
post-walk WalkContext (Form B = no user_listed_columns + table has
serial/shortid columns) and reports them on HintResolution; the note
fires only at the first slot so it doesn't repeat at every comma.
ambient_hint composes it onto the per-column prose.

tests/typing_surface/insert_form_b.rs

@@ -40,15 +40,18 @@ fn form_b_first_value_skips_serial_column() {
     let prose = hint_prose(&a).unwrap_or_else(|| {
         panic!("expected Prose at first Form B value slot, got {:?}", a.hint)
     });
-    // First column slot must name `Name`, not the skipped
-    // `id`.
+    // The value slot itself must be keyed on `Name` — the first
+    // non-auto column — not on the skipped `id`.
     assert!(
-        prose.contains("Name"),
-        "Form B should advance to first non-auto column `Name`, got prose: {prose:?}",
+        prose.starts_with("for `Name`"),
+        "Form B's first value slot should be for `Name`, got prose: {prose:?}",
     );
+    // `id` appears only inside the trailing pedagogical note
+    // (`id` auto-generated — skipped here …), never as the slot
+    // the user is being prompted to fill.
     assert!(
-        !prose.contains("`id`"),
-        "Form B should NOT prompt for the auto-gen `id`, got prose: {prose:?}",
+        !prose.starts_with("for `id`"),
+        "Form B must not prompt for the auto-gen `id` as a value slot, got prose: {prose:?}",
     );
     crate::snap!("form_b_first_value_serial_pk", a);
 }
@@ -218,6 +221,87 @@ fn form_b_text_pk_with_correct_values_parses() {
 // position.
 // =========================================================
 
+// =========================================================
+// Pedagogical Form-A pointer (handoff-12 §2.2).
+//
+// At the FIRST value slot of a Form B insert whose table has
+// auto-generated columns, the hint must mention the skipped
+// column(s) and point at the explicit-column form.
+// =========================================================
+
+#[test]
+fn form_b_first_slot_mentions_skipped_serial_column() {
+    let schema = schema_serial_pk();
+    let a = assess_at_end("insert into Customers values (", &schema);
+    let prose = hint_prose(&a).unwrap_or_else(|| {
+        panic!("expected Prose at first Form B slot, got {:?}", a.hint)
+    });
+    // Names the skipped auto-gen column.
+    assert!(
+        prose.contains("`id`"),
+        "first-slot hint should mention skipped `id`, got: {prose:?}",
+    );
+    // Points at the explicit-column escape hatch.
+    assert!(
+        prose.contains("auto-generated") && prose.contains("list columns"),
+        "first-slot hint should explain the Form-A escape, got: {prose:?}",
+    );
+    crate::snap!("form_b_first_slot_skip_note", a);
+}
+
+#[test]
+fn form_b_second_slot_omits_skip_note() {
+    // The note fires once, at the first slot only — not at
+    // every comma.
+    let schema = schema_serial_pk();
+    let a = assess_at_end(
+        "insert into Customers values ('Alice', ",
+        &schema,
+    );
+    let prose = hint_prose(&a).unwrap_or_else(|| {
+        panic!("expected Prose at second slot, got {:?}", a.hint)
+    });
+    assert!(
+        !prose.contains("auto-generated"),
+        "second-slot hint must NOT repeat the skip note, got: {prose:?}",
+    );
+    crate::snap!("form_b_second_slot_no_skip_note", a);
+}
+
+#[test]
+fn form_b_text_pk_has_no_skip_note() {
+    // No auto-gen columns → no skip note.
+    let schema = schema_text_pk();
+    let a = assess_at_end("insert into Items values (", &schema);
+    let prose = hint_prose(&a).unwrap_or_else(|| {
+        panic!("expected Prose, got {:?}", a.hint)
+    });
+    assert!(
+        !prose.contains("auto-generated"),
+        "text-PK table has no auto-gen column — no skip note expected, got: {prose:?}",
+    );
+    crate::snap!("form_b_text_pk_no_skip_note", a);
+}
+
+#[test]
+fn form_a_first_slot_has_no_skip_note() {
+    // Form A lists columns explicitly — the user is in control,
+    // no pedagogical pointer needed.
+    let schema = schema_serial_pk();
+    let a = assess_at_end(
+        "insert into Customers (Name) values (",
+        &schema,
+    );
+    let prose = hint_prose(&a).unwrap_or_else(|| {
+        panic!("expected Prose, got {:?}", a.hint)
+    });
+    assert!(
+        !prose.contains("auto-generated"),
+        "Form A must not show the Form-B skip note, got: {prose:?}",
+    );
+    crate::snap!("form_a_no_skip_note", a);
+}
+
 #[test]
 fn form_b_advances_through_every_type_first_to_real() {
     // Things' second column is `r:real`. After typing the