Insert grammar: Form C type-awareness via lookahead (ADR-0024 §Phase D)

Form C (`insert into T (vals)`) shared the `(` opener with Form A,
so its paren was an untyped Repeated(Choice(literal, ident)) — values
weren't type- or count-checked at parse time (handoff-12 §2.2).

New Node::Lookahead variant: a factory that peeks the source. The
insert first-paren factory inspects the first token — a value literal
routes the contents through the typed column_value_list (Form B
dispatch contract: per-non-auto-column typed slots); an identifier or
empty paren routes to a Form A column-name list. So Form C now gets
the same per-column typed slots, hints, and parse-time type/count
checking Form B has.

The explicit-Choice-branch split is impossible here (committed-choice
semantics commit after `(` matches); lookahead is the only route, and
DynamicSubgrammar factories couldn't see the source. Node::Lookahead
is not memoized — its output depends on source — but it returns only
a small node (a Repeated, or a thin DynamicSubgrammar wrapper that
delegates to the memoized column_value_list).

`insert into T (` now cleanly shows Form A column candidates instead
of mixed Form-A/C suggestions. Form C matrix tests updated for the
type-aware behaviour.

tests/typing_surface/insert_form_c.rs

@@ -1,24 +1,30 @@
 //! Matrix coverage for `insert into T (vals)` (Form C — bare
 //! value list, no `values` keyword).
 //!
-//! Form C shares the `( ... )` opener with Form A but resolves
-//! the paren contents as values rather than column names. Per
-//! handoff-12 §2.2 the Form C path is *type-unaware* — its
-//! grammar uses the schemaless `INSERT_PAREN_LIST` shape, not
-//! the typed `column_value_list`. Type validation happens at
-//! bind time, not parse time.
+//! Form C and Form B produce the identical AST and dispatch
+//! identically (`Insert { columns: None, … }`). As of the
+//! Form-C type-awareness work (handoff-14), Form C's paren is
+//! resolved by the `insert_first_paren` lookahead: a value
+//! literal as the first token routes the contents through the
+//! typed `column_value_list` — the same per-column typed slots
+//! Form B uses. So Form C values are now type-checked and
+//! count-checked at parse time, not only at bind time.
 //!
-//! The previous commit's Form C/A disambiguation means
-//! column-shaped items (idents) inside the parens now flag as
-//! "did you mean Form A?". This file pins both the happy-path
-//! (literals only) and the Form-A-recovery (column-shaped
-//! items).
+//! An identifier (column name) as the first token, or an empty
+//! paren, routes to Form A instead — `insert into T (Name)`
+//! still surfaces the "did you mean Form A?" recovery.
 
 use crate::typing_surface::*;
 use rdbms_playground::input_render::InputState;
 
+// =========================================================
+// Form C happy path: type-correct values parse to Insert.
+// =========================================================
+
 #[test]
-fn form_c_with_text_literals_parses() {
+fn form_c_text_pk_correct_values_parses() {
+    // Items(Code:text, Title:text) — Form C expects two text
+    // values (no auto-gen columns to skip).
     let schema = schema_text_pk();
     let a = assess_at_end(
         "insert into Items ('SKU-1', 'Widget')",
@@ -26,32 +32,128 @@ fn form_c_with_text_literals_parses() {
     );
     assert!(matches!(a.state, InputState::Valid));
     assert_eq!(a.parse_result.as_deref(), Ok("Insert"));
-    crate::snap!("form_c_text_literals", a);
+    crate::snap!("form_c_text_pk_valid", a);
 }
 
 #[test]
-fn form_c_with_mixed_literals_parses() {
+fn form_c_serial_pk_correct_values_parses() {
+    // Customers(id:serial, Name:text, Email:text) — Form C
+    // skips the serial `id`, expects two text values.
     let schema = schema_serial_pk();
     let a = assess_at_end(
-        "insert into Customers (1, 'Alice', 'a@b.c')",
+        "insert into Customers ('Alice', 'a@b.c')",
         &schema,
     );
     assert!(matches!(a.state, InputState::Valid));
     assert_eq!(a.parse_result.as_deref(), Ok("Insert"));
-    crate::snap!("form_c_mixed_literals", a);
+    crate::snap!("form_c_serial_pk_valid", a);
 }
 
 #[test]
-fn form_c_with_null_first_parses() {
+fn form_c_with_null_value_parses() {
+    // null is type-compatible with any slot.
     let schema = schema_serial_pk();
     let a = assess_at_end(
-        "insert into Customers (null, 'Alice', 'a@b.c')",
+        "insert into Customers (null, 'a@b.c')",
         &schema,
     );
     assert!(matches!(a.state, InputState::Valid));
-    crate::snap!("form_c_null_first", a);
+    crate::snap!("form_c_null_value", a);
 }
 
+// =========================================================
+// Form C is now type-aware (the §2.2 limitation is fixed).
+// =========================================================
+
+#[test]
+fn form_c_rejects_number_for_text_column() {
+    // `3.14` lands in the Name(text) slot — the typed slot
+    // rejects it at parse time. Before Form-C type-awareness
+    // this parsed Valid and only failed at bind time.
+    let schema = schema_serial_pk();
+    let a = assess_at_end(
+        "insert into Customers (3.14, 'a@b.c')",
+        &schema,
+    );
+    assert!(
+        !matches!(a.state, InputState::Valid),
+        "Form C should now type-check `3.14` against Name(text), got {:?}",
+        a.state,
+    );
+    crate::snap!("form_c_type_mismatch", a);
+}
+
+#[test]
+fn form_c_wrong_value_count_is_invalid() {
+    // Customers Form C expects exactly two values (id:serial
+    // skipped). Three values is a count mismatch — caught at
+    // parse time now.
+    let schema = schema_serial_pk();
+    let a = assess_at_end(
+        "insert into Customers ('Alice', 'a@b.c', 'extra')",
+        &schema,
+    );
+    assert!(
+        !matches!(a.state, InputState::Valid),
+        "Form C with too many values must be invalid, got {:?}",
+        a.state,
+    );
+    crate::snap!("form_c_wrong_count", a);
+}
+
+// =========================================================
+// Form C typed-slot prose — the per-column hint Form B has
+// is now available in Form C too.
+// =========================================================
+
+#[test]
+fn form_c_second_slot_shows_typed_prose_for_column() {
+    // First token `'Alice'` is a string literal → Form C. At
+    // the second slot the hint names the Email column.
+    let schema = schema_serial_pk();
+    let a = assess_at_end(
+        "insert into Customers ('Alice', ",
+        &schema,
+    );
+    let prose = hint_prose(&a).unwrap_or_else(|| {
+        panic!("expected Prose at Form C second slot, got {:?}", a.hint)
+    });
+    assert!(
+        prose.contains("Email"),
+        "Form C second slot should name `Email`, got prose: {prose:?}",
+    );
+    crate::snap!("form_c_typed_prose", a);
+}
+
+// =========================================================
+// In-progress Form C classifies as IncompleteAtEof.
+// =========================================================
+
+#[test]
+fn form_c_in_progress_after_comma_is_incomplete() {
+    let schema = schema_serial_pk();
+    let a = assess_at_end("insert into Customers ('Alice', ", &schema);
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    crate::snap!("form_c_in_progress_after_comma", a);
+}
+
+#[test]
+fn form_c_in_progress_without_close_paren_is_incomplete() {
+    let schema = schema_serial_pk();
+    let a = assess_at_end(
+        "insert into Customers ('Alice', 'a@b.c'",
+        &schema,
+    );
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    crate::snap!("form_c_in_progress_no_close", a);
+}
+
+// =========================================================
+// Form A recovery: a column-name identifier as the first
+// paren token routes to Form A — `insert into T (Name)`
+// without `values` flags as Form-A-in-progress.
+// =========================================================
+
 #[test]
 fn form_c_with_column_shaped_item_flags_as_form_a_in_progress() {
     let schema = schema_serial_pk();
@@ -73,37 +175,3 @@ fn form_c_with_two_columns_flags_as_form_a_in_progress() {
     assert_candidate_present(&a, &["values"]);
     crate::snap!("form_c_two_columns_recovery", a);
 }
-
-#[test]
-fn form_c_type_unaware_grammar_accepts_decimal_for_int_column() {
-    // Form C's grammar uses INSERT_PAREN_LIST (the pre-Phase-D
-    // schemaless choice), so type mismatches aren't caught at
-    // parse time. Bind time catches them. Handoff §2.2
-    // documents this as known.
-    let schema = schema_serial_pk();
-    let a = assess_at_end(
-        "insert into Customers (3.14, 'Alice', 'a@b.c')",
-        &schema,
-    );
-    assert!(matches!(a.state, InputState::Valid));
-    crate::snap!("form_c_type_unaware", a);
-}
-
-#[test]
-fn form_c_in_progress_after_comma_is_incomplete() {
-    let schema = schema_serial_pk();
-    let a = assess_at_end("insert into Customers (1, ", &schema);
-    assert!(matches!(a.state, InputState::IncompleteAtEof));
-    crate::snap!("form_c_in_progress_after_comma", a);
-}
-
-#[test]
-fn form_c_in_progress_without_close_paren_is_incomplete() {
-    let schema = schema_serial_pk();
-    let a = assess_at_end(
-        "insert into Customers (1, 'Alice'",
-        &schema,
-    );
-    assert!(matches!(a.state, InputState::IncompleteAtEof));
-    crate::snap!("form_c_in_progress_no_close", a);
-}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_a__after_open_paren_offers_active_table_columns_only@after_open_paren_multi_table.snap

@@ -8,9 +8,19 @@ Assessment {
     cursor: 23,
     state: IncompleteAtEof,
     hint: Some(
-        Prose(
-            "Type a value: number, 'text', true/false, null (dates as 'YYYY-MM-DD', datetimes as 'YYYY-MM-DDTHH:MM:SS')",
-        ),
+        Candidates {
+            items: [
+                Candidate {
+                    text: "Name",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "id",
+                    kind: Identifier,
+                },
+            ],
+            selected: None,
+        },
     ),
     completion: Some(
         Completion {
@@ -20,18 +30,6 @@ Assessment {
             ),
             partial_prefix: "",
             candidates: [
-                Candidate {
-                    text: "null",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "true",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "false",
-                    kind: Keyword,
-                },
                 Candidate {
                     text: "Name",
                     kind: Identifier,

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_a__after_open_paren_serial_pk_offers_all_columns_including_serial@after_open_paren_serial_pk.snap

@@ -8,9 +8,23 @@ Assessment {
     cursor: 23,
     state: IncompleteAtEof,
     hint: Some(
-        Prose(
-            "Type a value: number, 'text', true/false, null (dates as 'YYYY-MM-DD', datetimes as 'YYYY-MM-DDTHH:MM:SS')",
-        ),
+        Candidates {
+            items: [
+                Candidate {
+                    text: "Email",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "Name",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "id",
+                    kind: Identifier,
+                },
+            ],
+            selected: None,
+        },
     ),
     completion: Some(
         Completion {
@@ -20,18 +34,6 @@ Assessment {
             ),
             partial_prefix: "",
             candidates: [
-                Candidate {
-                    text: "null",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "true",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "false",
-                    kind: Keyword,
-                },
                 Candidate {
                     text: "Email",
                     kind: Identifier,

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_a__after_open_paren_text_pk_offers_text_pk_columns@after_open_paren_text_pk.snap

@@ -8,9 +8,19 @@ Assessment {
     cursor: 19,
     state: IncompleteAtEof,
     hint: Some(
-        Prose(
-            "Type a value: number, 'text', true/false, null (dates as 'YYYY-MM-DD', datetimes as 'YYYY-MM-DDTHH:MM:SS')",
-        ),
+        Candidates {
+            items: [
+                Candidate {
+                    text: "Code",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "Title",
+                    kind: Identifier,
+                },
+            ],
+            selected: None,
+        },
     ),
     completion: Some(
         Completion {
@@ -20,18 +30,6 @@ Assessment {
             ),
             partial_prefix: "",
             candidates: [
-                Candidate {
-                    text: "null",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "true",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "false",
-                    kind: Keyword,
-                },
                 Candidate {
                     text: "Code",
                     kind: Identifier,

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_a__form_a_open_paren_no_leakage_from_other_tables@form_a_open_paren_orders.snap

@@ -8,9 +8,23 @@ Assessment {
     cursor: 20,
     state: IncompleteAtEof,
     hint: Some(
-        Prose(
-            "Type a value: number, 'text', true/false, null (dates as 'YYYY-MM-DD', datetimes as 'YYYY-MM-DDTHH:MM:SS')",
-        ),
+        Candidates {
+            items: [
+                Candidate {
+                    text: "CustId",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "OrderId",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "Total",
+                    kind: Identifier,
+                },
+            ],
+            selected: None,
+        },
     ),
     completion: Some(
         Completion {
@@ -20,18 +34,6 @@ Assessment {
             ),
             partial_prefix: "",
             candidates: [
-                Candidate {
-                    text: "null",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "true",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "false",
-                    kind: Keyword,
-                },
                 Candidate {
                     text: "CustId",
                     kind: Identifier,

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_a__mid_column_list_after_comma_offers_remaining_columns@after_comma_in_column_list.snap

@@ -8,9 +8,23 @@ Assessment {
     cursor: 27,
     state: IncompleteAtEof,
     hint: Some(
-        Prose(
-            "Type a value: number, 'text', true/false, null (dates as 'YYYY-MM-DD', datetimes as 'YYYY-MM-DDTHH:MM:SS')",
-        ),
+        Candidates {
+            items: [
+                Candidate {
+                    text: "Email",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "Name",
+                    kind: Identifier,
+                },
+                Candidate {
+                    text: "id",
+                    kind: Identifier,
+                },
+            ],
+            selected: None,
+        },
     ),
     completion: Some(
         Completion {
@@ -20,18 +34,6 @@ Assessment {
             ),
             partial_prefix: "",
             candidates: [
-                Candidate {
-                    text: "null",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "true",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "false",
-                    kind: Keyword,
-                },
                 Candidate {
                     text: "Email",
                     kind: Identifier,

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_c__form_c_in_progress_after_comma_is_incomplete@form_c_in_progress_after_comma.snap

@@ -1,22 +1,22 @@
 ---
 source: tests/typing_surface/insert_form_c.rs
-description: "input=\"insert into Customers (1, \" cursor=26"
+description: "input=\"insert into Customers ('Alice', \" cursor=32"
 expression: "& a"
 ---
 Assessment {
-    input: "insert into Customers (1, ",
-    cursor: 26,
+    input: "insert into Customers ('Alice', ",
+    cursor: 32,
     state: IncompleteAtEof,
     hint: Some(
         Prose(
-            "Type a value: number, 'text', true/false, null (dates as 'YYYY-MM-DD', datetimes as 'YYYY-MM-DDTHH:MM:SS')",
+            "for `Email`: Type a quoted string (e.g. 'Alice') or null",
         ),
     ),
     completion: Some(
         Completion {
             replaced_range: (
-                26,
-                26,
+                32,
+                32,
             ),
             partial_prefix: "",
             candidates: [
@@ -24,26 +24,6 @@ Assessment {
                     text: "null",
                     kind: Keyword,
                 },
-                Candidate {
-                    text: "true",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "false",
-                    kind: Keyword,
-                },
-                Candidate {
-                    text: "Email",
-                    kind: Identifier,
-                },
-                Candidate {
-                    text: "Name",
-                    kind: Identifier,
-                },
-                Candidate {
-                    text: "id",
-                    kind: Identifier,
-                },
             ],
         },
     ),

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_c__form_c_in_progress_without_close_paren_is_incomplete@form_c_in_progress_no_close.snap

@@ -1,11 +1,11 @@
 ---
 source: tests/typing_surface/insert_form_c.rs
-description: "input=\"insert into Customers (1, 'Alice'\" cursor=33"
+description: "input=\"insert into Customers ('Alice', 'a@b.c'\" cursor=39"
 expression: "& a"
 ---
 Assessment {
-    input: "insert into Customers (1, 'Alice'",
-    cursor: 33,
+    input: "insert into Customers ('Alice', 'a@b.c'",
+    cursor: 39,
     state: IncompleteAtEof,
     hint: Some(
         Prose(

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_c__form_c_rejects_number_for_text_column@form_c_type_mismatch.snap

@@ -0,0 +1,35 @@
+---
+source: tests/typing_surface/insert_form_c.rs
+description: "input=\"insert into Customers (3.14, 'a@b.c')\" cursor=37"
+expression: "& a"
+---
+Assessment {
+    input: "insert into Customers (3.14, 'a@b.c')",
+    cursor: 37,
+    state: DefiniteErrorAt(
+        23,
+    ),
+    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: (
+                37,
+                37,
+            ),
+            partial_prefix: "",
+            candidates: [
+                Candidate {
+                    text: "null",
+                    kind: Keyword,
+                },
+            ],
+        },
+    ),
+    parse_result: Err(
+        "Invalid(definite)",
+    ),
+}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_c__form_c_second_slot_shows_typed_prose_for_column@form_c_typed_prose.snap

@@ -0,0 +1,33 @@
+---
+source: tests/typing_surface/insert_form_c.rs
+description: "input=\"insert into Customers ('Alice', \" cursor=32"
+expression: "& a"
+---
+Assessment {
+    input: "insert into Customers ('Alice', ",
+    cursor: 32,
+    state: IncompleteAtEof,
+    hint: Some(
+        Prose(
+            "for `Email`: Type a quoted string (e.g. 'Alice') or null",
+        ),
+    ),
+    completion: Some(
+        Completion {
+            replaced_range: (
+                32,
+                32,
+            ),
+            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_c__form_c_serial_pk_correct_values_parses@form_c_serial_pk_valid.snap

@@ -1,11 +1,11 @@
 ---
 source: tests/typing_surface/insert_form_c.rs
-description: "input=\"insert into Customers (1, 'Alice', 'a@b.c')\" cursor=43"
+description: "input=\"insert into Customers ('Alice', 'a@b.c')\" cursor=40"
 expression: "& a"
 ---
 Assessment {
-    input: "insert into Customers (1, 'Alice', 'a@b.c')",
-    cursor: 43,
+    input: "insert into Customers ('Alice', 'a@b.c')",
+    cursor: 40,
     state: Valid,
     hint: Some(
         Candidates {
@@ -21,8 +21,8 @@ Assessment {
     completion: Some(
         Completion {
             replaced_range: (
-                43,
-                43,
+                40,
+                40,
             ),
             partial_prefix: "",
             candidates: [

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_c__form_c_with_null_first_parses@form_c_null_first.snap

@@ -1,39 +0,0 @@
----
-source: tests/typing_surface/insert_form_c.rs
-description: "input=\"insert into Customers (null, 'Alice', 'a@b.c')\" cursor=46"
-expression: "& a"
----
-Assessment {
-    input: "insert into Customers (null, 'Alice', 'a@b.c')",
-    cursor: 46,
-    state: Valid,
-    hint: Some(
-        Candidates {
-            items: [
-                Candidate {
-                    text: "values",
-                    kind: Keyword,
-                },
-            ],
-            selected: None,
-        },
-    ),
-    completion: Some(
-        Completion {
-            replaced_range: (
-                46,
-                46,
-            ),
-            partial_prefix: "",
-            candidates: [
-                Candidate {
-                    text: "values",
-                    kind: Keyword,
-                },
-            ],
-        },
-    ),
-    parse_result: Ok(
-        "Insert",
-    ),
-}

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_c__form_c_with_null_value_parses@form_c_null_value.snap

@@ -1,11 +1,11 @@
 ---
 source: tests/typing_surface/insert_form_c.rs
-description: "input=\"insert into Customers (3.14, 'Alice', 'a@b.c')\" cursor=46"
+description: "input=\"insert into Customers (null, 'a@b.c')\" cursor=37"
 expression: "& a"
 ---
 Assessment {
-    input: "insert into Customers (3.14, 'Alice', 'a@b.c')",
-    cursor: 46,
+    input: "insert into Customers (null, 'a@b.c')",
+    cursor: 37,
     state: Valid,
     hint: Some(
         Candidates {
@@ -21,8 +21,8 @@ Assessment {
     completion: Some(
         Completion {
             replaced_range: (
-                46,
-                46,
+                37,
+                37,
             ),
             partial_prefix: "",
             candidates: [

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__insert_form_c__form_c_wrong_value_count_is_invalid@form_c_wrong_count.snap

@@ -0,0 +1,21 @@
+---
+source: tests/typing_surface/insert_form_c.rs
+description: "input=\"insert into Customers ('Alice', 'a@b.c', 'extra')\" cursor=49"
+expression: "& a"
+---
+Assessment {
+    input: "insert into Customers ('Alice', 'a@b.c', 'extra')",
+    cursor: 49,
+    state: DefiniteErrorAt(
+        39,
+    ),
+    hint: Some(
+        Prose(
+            "Submit with Enter",
+        ),
+    ),
+    completion: None,
+    parse_result: Err(
+        "Invalid(definite)",
+    ),
+}