fix(server): invalidate executor cache after dropping databases

Executors were cached with stale database manager references, causing dropped
databases to still appear in SHOW DATABASES queries. Added invalidateAllExecutors()
and call it after DropDatabase() and DropCompositeDatabase() operations to ensure
fresh executor references see the updated database list.

Fixes TestMultiDatabase_E2E_FullSequence test failures in Step12 and Step13.

Author: orneryd

pkg/multidb/composite.go

@@ -135,7 +135,14 @@ func (m *DatabaseManager) DropCompositeDatabase(name string) error {
 	delete(m.databases, name)
 	delete(m.engines, name) // Clear cached engine
 
-	return m.persistMetadata()
+	if err := m.persistMetadata(); err != nil {
+		// If persistence fails, restore the database to maintain consistency
+		// This prevents the database from being dropped in memory but still existing in storage
+		m.databases[name] = info
+		return fmt.Errorf("failed to persist metadata after drop: %w", err)
+	}
+
+	return nil
 }
 
 // AddConstituent adds a constituent to an existing composite database.

pkg/multidb/manager.go

@@ -379,7 +379,14 @@ func (m *DatabaseManager) DropDatabase(name string) error {
 	delete(m.databases, name)
 	delete(m.engines, name) // Clear cached engine
 
-	return m.persistMetadata()
+	if err := m.persistMetadata(); err != nil {
+		// If persistence fails, restore the database to maintain consistency
+		// This prevents the database from being dropped in memory but still existing in storage
+		m.databases[name] = info
+		return fmt.Errorf("failed to persist metadata after drop: %w", err)
+	}
+
+	return nil
 }
 
 // GetStorage returns a namespaced storage engine for the specified database.

pkg/server/server_db.go

@@ -142,6 +142,16 @@ func (s *Server) invalidateExecutor(dbName string) {
 	delete(s.executors, dbName)
 }
 
+// invalidateAllExecutors clears all cached executors to force fresh database manager references.
+// This is used when database metadata changes (e.g., dropping databases) to ensure
+// all executors see the updated state.
+func (s *Server) invalidateAllExecutors() {
+	s.executorsMu.Lock()
+	defer s.executorsMu.Unlock()
+	// Clear all executors - they will be recreated with fresh database manager references
+	s.executors = make(map[string]*cypher.StorageExecutor)
+}
+
 // databaseManagerAdapter wraps multidb.DatabaseManager to implement
 // cypher.DatabaseManagerInterface, avoiding import cycles.
 type databaseManagerAdapter struct {
@@ -165,6 +175,9 @@ func (a *databaseManagerAdapter) DropDatabase(name string) error {
 	// Invalidate cached executor for dropped database
 	if a.server != nil {
 		a.server.invalidateExecutor(name)
+		// Also invalidate all executors to ensure fresh database manager references
+		// This ensures queries from other databases see the updated database list
+		a.server.invalidateAllExecutors()
 	}
 	return nil
 }
@@ -238,8 +251,15 @@ func (a *databaseManagerAdapter) DropCompositeDatabase(name string) error {
 	if err := a.manager.DropCompositeDatabase(name); err != nil {
 		return err
 	}
-	// Note: Composite databases don't have their own executors cached
-	// since queries go through constituent databases. No cleanup needed.
+	// Invalidate any cached executors that might reference this composite database
+	// Note: Composite databases don't have their own executors cached, but we should
+	// invalidate the executor for the database we're querying from (usually "nornic")
+	// to ensure subsequent queries see the updated state
+	if a.server != nil {
+		// Invalidate executor cache to force fresh database manager reference
+		// This ensures all executors see the updated database list
+		a.server.invalidateAllExecutors()
+	}
 	return nil
 }