test: align merged fixture contracts

packages/coding-agent/test/modes/utils/render-initial-messages.test.ts

@@ -62,7 +62,7 @@ function makeCtx(): {
 
 	const ctx = {
 		chatContainer: { clear: vi.fn(), addChild: vi.fn() },
-		pendingMessagesContainer: { clear: vi.fn() },
+		pendingMessagesContainer: { clear: vi.fn(), disposeChildren: vi.fn() },
 		pendingBashComponents: [],
 		pendingPythonComponents: [],
 		session: { buildTranscriptSessionContext: transcriptSpy },