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/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(