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

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_b__form_a_first_slot_has_no_skip_note@form_a_no_skip_note.snap

@@ -0,0 +1,33 @@
+---
+source: tests/typing_surface/insert_form_b.rs
+description: "input=\"insert into Customers (Name) values (\" cursor=37"
+expression: "& a"
+---
+Assessment {
+    input: "insert into Customers (Name) values (",
+    cursor: 37,
+    state: IncompleteAtEof,
+    hint: Some(
+        Prose(
+            "for `Name`: Type a quoted string (e.g. 'Alice') or null",
+        ),
+    ),
+    completion: Some(
+        Completion {
+            replaced_range: (
+                37,
+                37,
+            ),
+            partial_prefix: "",
+            candidates: [
+                Candidate {
+                    text: "null",
+                    kind: Keyword,
+                },
+            ],
+        },
+    ),
+    parse_result: Err(
+        "Invalid(at_eof)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_b__form_b_first_slot_mentions_skipped_serial_column@form_b_first_slot_skip_note.snap

@@ -0,0 +1,33 @@
+---
+source: tests/typing_surface/insert_form_b.rs
+description: "input=\"insert into Customers values (\" cursor=30"
+expression: "& a"
+---
+Assessment {
+    input: "insert into Customers values (",
+    cursor: 30,
+    state: IncompleteAtEof,
+    hint: Some(
+        Prose(
+            "for `Name`: Type a quoted string (e.g. 'Alice') or null (`id` auto-generated — skipped here; list columns explicitly, e.g. `insert into T (...) values (...)`, to set it.)",
+        ),
+    ),
+    completion: Some(
+        Completion {
+            replaced_range: (
+                30,
+                30,
+            ),
+            partial_prefix: "",
+            candidates: [
+                Candidate {
+                    text: "null",
+                    kind: Keyword,
+                },
+            ],
+        },
+    ),
+    parse_result: Err(
+        "Invalid(at_eof)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_b__form_b_first_value_every_type_first_column_is_int@form_b_first_value_every_type.snap

@@ -9,7 +9,7 @@ Assessment {
     state: IncompleteAtEof,
     hint: Some(
         Prose(
-            "for `k`: Type an integer (e.g. 42, -7) or null",
+            "for `k`: Type an integer (e.g. 42, -7) or null (`sid`, `auto` auto-generated — skipped here; list columns explicitly, e.g. `insert into T (...) values (...)`, to set it.)",
         ),
     ),
     completion: Some(

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_b__form_b_first_value_skips_serial_column@form_b_first_value_serial_pk.snap

@@ -9,7 +9,7 @@ Assessment {
     state: IncompleteAtEof,
     hint: Some(
         Prose(
-            "for `Name`: Type a quoted string (e.g. 'Alice') or null",
+            "for `Name`: Type a quoted string (e.g. 'Alice') or null (`id` auto-generated — skipped here; list columns explicitly, e.g. `insert into T (...) values (...)`, to set it.)",
         ),
     ),
     completion: Some(

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_b__form_b_second_slot_omits_skip_note@form_b_second_slot_no_skip_note.snap

@@ -0,0 +1,33 @@
+---
+source: tests/typing_surface/insert_form_b.rs
+description: "input=\"insert into Customers values ('Alice', \" cursor=39"
+expression: "& a"
+---
+Assessment {
+    input: "insert into Customers values ('Alice', ",
+    cursor: 39,
+    state: IncompleteAtEof,
+    hint: Some(
+        Prose(
+            "for `Email`: Type a quoted string (e.g. 'Alice') or null",
+        ),
+    ),
+    completion: Some(
+        Completion {
+            replaced_range: (
+                39,
+                39,
+            ),
+            partial_prefix: "",
+            candidates: [
+                Candidate {
+                    text: "null",
+                    kind: Keyword,
+                },
+            ],
+        },
+    ),
+    parse_result: Err(
+        "Invalid(at_eof)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_b__form_b_text_pk_has_no_skip_note@form_b_text_pk_no_skip_note.snap

@@ -0,0 +1,33 @@
+---
+source: tests/typing_surface/insert_form_b.rs
+description: "input=\"insert into Items values (\" cursor=26"
+expression: "& a"
+---
+Assessment {
+    input: "insert into Items values (",
+    cursor: 26,
+    state: IncompleteAtEof,
+    hint: Some(
+        Prose(
+            "for `Code`: Type a quoted string (e.g. 'Alice') or null",
+        ),
+    ),
+    completion: Some(
+        Completion {
+            replaced_range: (
+                26,
+                26,
+            ),
+            partial_prefix: "",
+            candidates: [
+                Candidate {
+                    text: "null",
+                    kind: Keyword,
+                },
+            ],
+        },
+    ),
+    parse_result: Err(
+        "Invalid(at_eof)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_b__form_b_with_extra_value_for_serial_column_is_invalid@form_b_extra_serial_value.snap

@@ -11,7 +11,7 @@ Assessment {
     ),
     hint: Some(
         Prose(
-            "for `Name`: Type a quoted string (e.g. 'Alice') or null",
+            "for `Name`: Type a quoted string (e.g. 'Alice') or null (`id` auto-generated — skipped here; list columns explicitly, e.g. `insert into T (...) values (...)`, to set it.)",
         ),
     ),
     completion: Some(