DDL grammar: writes_table on table-name slots for column narrowing

Handoff-12 §2.2: the DDL TABLE_NAME_EXISTING slot and the
relationship-endpoint table idents didn't set writes_table, so
column-name slots downstream (drop/rename/change column; relationship
qualified columns) couldn't narrow to the active table — candidates
leaked from every table. Set writes_table: true on TABLE_NAME_EXISTING
and on DR_PARENT/DR_CHILD/AR_PARENT/AR_CHILD table idents. The
deliberately-documenting completion test now asserts per-table
narrowing.

src/dsl/grammar/ddl.rs

@@ -34,12 +34,19 @@ const TABLE_NAME_NEW: Node = Node::Ident {
         writes_user_listed_column: false,
 };
 
+// `writes_table: true` so that the column-name slots that
+// follow the table name in `drop column` / `rename column` /
+// `change column` / `add column` can narrow their candidates to
+// this table's columns (handoff-12 §2.2). The walker writes
+// `current_table` / `current_table_columns` on match; the
+// completion engine reads the snapshot. `drop table` has no
+// downstream column slot, so the write is harmless there.
 const TABLE_NAME_EXISTING: Node = Node::Ident {
     source: IdentSource::Tables,
     role: "table_name",
     validator: None,
     highlight_override: None,
-        writes_table: false,
+        writes_table: true,
         writes_column: false,
         writes_user_listed_column: false,
 };
@@ -118,13 +125,19 @@ const DROP_COLUMN: Node = Node::Seq(DROP_COLUMN_NODES);
 // drop_relationship — `drop relationship (endpoints | name)`
 // =================================================================
 
+// `writes_table: true` on each endpoint's table ident so the
+// `.<col>` slot that follows narrows to that table's columns
+// (handoff-13 §2.2 follow-up). The two endpoints are walked
+// sequentially, so `current_table` is correctly the parent
+// table while walking `parent_column` and the child table
+// while walking `child_column`.
 const DR_PARENT_NODES: &[Node] = &[
     Node::Ident {
         source: IdentSource::Tables,
         role: "parent_table",
         validator: None,
         highlight_override: None,
-        writes_table: false,
+        writes_table: true,
         writes_column: false,
         writes_user_listed_column: false,
     },
@@ -147,7 +160,7 @@ const DR_CHILD_NODES: &[Node] = &[
         role: "child_table",
         validator: None,
         highlight_override: None,
-        writes_table: false,
+        writes_table: true,
         writes_column: false,
         writes_user_listed_column: false,
     },
@@ -212,13 +225,16 @@ const ADD_COLUMN: Node = Node::Seq(ADD_COLUMN_NODES);
 //                    [--create-fk]`
 // =================================================================
 
+// `writes_table: true` on each endpoint's table ident so the
+// `.<col>` slot narrows to that table's columns (handoff-13
+// §2.2 follow-up — mirrors DR_PARENT / DR_CHILD).
 const AR_PARENT_NODES: &[Node] = &[
     Node::Ident {
         source: IdentSource::Tables,
         role: "parent_table",
         validator: None,
         highlight_override: None,
-        writes_table: false,
+        writes_table: true,
         writes_column: false,
         writes_user_listed_column: false,
     },
@@ -241,7 +257,7 @@ const AR_CHILD_NODES: &[Node] = &[
         role: "child_table",
         validator: None,
         highlight_override: None,
-        writes_table: false,
+        writes_table: true,
         writes_column: false,
         writes_user_listed_column: false,
     },