Matrix: create table, DDL, and app-command coverage

55 tests covering create table, drop column, drop relationship
(endpoints + by-name), add relationship, rename/change column, and
all app-lifecycle commands. The drop-column and relationship tests
drove the §2.2 writes_table fix in the previous commit.

Documents one UX wrinkle as a flagged finding: partial entry words
(`qu`) classify as DefiniteErrorAt — same as unknown commands —
because the walker only engages on a complete entry word.

859 baseline -> 989 passing; 1 ignored (pre-existing doc-test).

tests/typing_surface/drop_column.rs

@@ -1 +1,72 @@
-//! Submodule stub — populated in subsequent tasks.
+//! Matrix coverage for `drop column [from] [table] <T> : <col>`
+//! (ADR-0013).
+//!
+//! Handoff-12 §2.2 flagged that the DDL `TABLE_NAME_EXISTING`
+//! slot didn't set `writes_table`, so at `drop column from T: `
+//! the column-name slot couldn't narrow to T's columns —
+//! candidates leaked from every table. This file asserts the
+//! per-table narrowing; the fix lands alongside it.
+
+use crate::typing_surface::*;
+use rdbms_playground::input_render::InputState;
+
+#[test]
+fn after_drop_column_offers_table_names() {
+    let schema = schema_multi_table();
+    let a = assess_at_end("drop column from ", &schema);
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    assert_candidate_present(&a, &["Customers", "Orders"]);
+    crate::snap!("after_from", a);
+}
+
+#[test]
+fn after_table_name_expects_colon() {
+    let schema = schema_serial_pk();
+    let a = assess_at_end("drop column from Customers", &schema);
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    crate::snap!("after_table_name", a);
+}
+
+// =========================================================
+// Handoff §2.2 — column slot narrows to the active table.
+// =========================================================
+
+#[test]
+fn after_colon_offers_only_active_table_columns_no_leakage() {
+    let schema = schema_multi_table();
+    let a = assess_at_end("drop column from Customers: ", &schema);
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    // Customers's columns must be offered.
+    assert_candidate_present(&a, &["id", "Name"]);
+    // Orders's columns must NOT leak.
+    assert_no_candidate_named(&a, &["OrderId", "CustId", "Total"]);
+    crate::snap!("after_colon_multi_table", a);
+}
+
+#[test]
+fn after_colon_serial_pk_offers_all_columns() {
+    let schema = schema_serial_pk();
+    let a = assess_at_end("drop column from Customers: ", &schema);
+    assert_candidate_present(&a, &["id", "Name", "Email"]);
+    crate::snap!("after_colon_serial_pk", a);
+}
+
+#[test]
+fn complete_drop_column_parses() {
+    let schema = schema_serial_pk();
+    let a = assess_at_end("drop column from Customers: Email", &schema);
+    assert!(matches!(a.state, InputState::Valid));
+    assert_eq!(a.parse_result.as_deref(), Ok("DropColumn"));
+    crate::snap!("complete_drop_column", a);
+}
+
+#[test]
+fn drop_column_with_table_keyword_parses() {
+    let schema = schema_serial_pk();
+    let a = assess_at_end(
+        "drop column from table Customers: Email",
+        &schema,
+    );
+    assert!(matches!(a.state, InputState::Valid));
+    crate::snap!("with_table_keyword", a);
+}