refactor(schema): fan desired-state schema out to one file per table (#8131)

schema/functions/attach_community_write_fence.sql

@@ -0,0 +1,45 @@
+-- Attach the universal fence to one community-scoped relation. Future
+-- migrations must invoke this helper explicitly after CREATE/ALTER introduces
+-- community_id; the migration lint enforces that contract.
+CREATE FUNCTION attach_community_write_fence(target REGCLASS) RETURNS VOID
+LANGUAGE plpgsql AS $$
+DECLARE
+    relation_name NAME;
+BEGIN
+    SELECT c.relname
+      INTO relation_name
+      FROM pg_class c
+      JOIN pg_namespace n ON n.oid = c.relnamespace
+     WHERE c.oid = target
+       AND n.nspname = current_schema()
+       AND c.relkind IN ('r', 'p')
+       AND NOT c.relispartition;
+    IF NOT FOUND THEN
+        RAISE EXCEPTION 'community write fence target % is not a table in the current schema', target
+            USING ERRCODE = 'wrong_object_type';
+    END IF;
+    IF community_write_fence_excluded_table(relation_name) THEN
+        RETURN;
+    END IF;
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_attribute
+         WHERE attrelid = target AND attname = 'community_id' AND NOT attisdropped
+    ) THEN
+        RAISE EXCEPTION 'community write fence target % has no community_id', target
+            USING ERRCODE = 'undefined_column';
+    END IF;
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_trigger
+         WHERE tgrelid = target
+           AND tgname = 'community_write_fence_' || relation_name
+           AND NOT tgisinternal
+    ) THEN
+        EXECUTE format(
+            'CREATE TRIGGER %I BEFORE INSERT OR UPDATE OR DELETE ON %s '
+            'FOR EACH ROW EXECUTE FUNCTION enforce_community_write_fence()',
+            'community_write_fence_' || relation_name,
+            target
+        );
+    END IF;
+END
+$$;