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_relationship.rs

@@ -1 +1,108 @@
-//! Submodule stub — populated in subsequent tasks.
+//! Matrix coverage for `drop relationship (endpoints | name)`
+//! (ADR-0013).
+//!
+//! Two selector forms:
+//! - by endpoints: `drop relationship from P.c to C.c`
+//! - by name: `drop relationship <name>`
+//!
+//! Handoff-12 §2.2 noted the qualified-column slots
+//! (`from T.col`) don't narrow to T's columns. The fix lands
+//! alongside the matrix where the test asserts narrowing.
+
+use crate::typing_surface::*;
+use rdbms_playground::completion::SchemaCache;
+use rdbms_playground::input_render::InputState;
+
+/// schema_multi_table + a named relationship in the cache so
+/// the by-name selector has a candidate.
+fn schema_with_relationship() -> SchemaCache {
+    let mut cache = schema_multi_table();
+    cache
+        .relationships
+        .push("Orders_CustId_to_Customers".to_string());
+    cache
+}
+
+#[test]
+fn after_relationship_keyword_offers_from_and_names() {
+    let schema = schema_with_relationship();
+    let a = assess_at_end("drop relationship ", &schema);
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    // Both selector forms discoverable: `from` for endpoints,
+    // the relationship name for the by-name form.
+    assert_candidate_present(
+        &a,
+        &["from", "Orders_CustId_to_Customers"],
+    );
+    crate::snap!("after_relationship_keyword", a);
+}
+
+#[test]
+fn after_from_offers_table_names() {
+    let schema = schema_with_relationship();
+    let a = assess_at_end("drop relationship from ", &schema);
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    assert_candidate_present(&a, &["Customers", "Orders"]);
+    crate::snap!("after_from", a);
+}
+
+#[test]
+fn after_parent_table_dot_narrows_to_parent_columns() {
+    // §2.2 follow-up: `from Orders.` should narrow the
+    // column slot to Orders's columns.
+    let schema = schema_with_relationship();
+    let a = assess_at_end("drop relationship from Orders.", &schema);
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    assert_candidate_present(&a, &["OrderId", "CustId", "Total"]);
+    assert_no_candidate_named(&a, &["Name"]);
+    crate::snap!("after_parent_dot", a);
+}
+
+#[test]
+fn after_to_offers_table_names() {
+    let schema = schema_with_relationship();
+    let a = assess_at_end(
+        "drop relationship from Orders.CustId to ",
+        &schema,
+    );
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    assert_candidate_present(&a, &["Customers", "Orders"]);
+    crate::snap!("after_to", a);
+}
+
+#[test]
+fn after_child_table_dot_narrows_to_child_columns() {
+    let schema = schema_with_relationship();
+    let a = assess_at_end(
+        "drop relationship from Orders.CustId to Customers.",
+        &schema,
+    );
+    assert!(matches!(a.state, InputState::IncompleteAtEof));
+    assert_candidate_present(&a, &["id", "Name"]);
+    assert_no_candidate_named(&a, &["OrderId", "CustId", "Total"]);
+    crate::snap!("after_child_dot", a);
+}
+
+#[test]
+fn complete_drop_relationship_by_endpoints_parses() {
+    let schema = schema_with_relationship();
+    let a = assess_at_end(
+        "drop relationship from Orders.CustId to Customers.id",
+        &schema,
+    );
+    assert!(matches!(a.state, InputState::Valid));
+    assert_eq!(a.parse_result.as_deref(), Ok("DropRelationship"));
+    crate::snap!("complete_by_endpoints", a);
+}
+
+#[test]
+fn complete_drop_relationship_by_name_parses() {
+    let schema = schema_with_relationship();
+    let a = assess_at_end(
+        "drop relationship Orders_CustId_to_Customers",
+        &schema,
+    );
+    assert!(matches!(a.state, InputState::Valid));
+    assert_eq!(a.parse_result.as_deref(), Ok("DropRelationship"));
+    crate::snap!("complete_by_name", a);
+}