test(task): stubbed setIrcWakeTurnObserver on executor session fakes

- The IRC wake monitor from PR #7108 calls the observer on every kept-alive
  subagent finalize; fakes across the executor suites predate the method
  and threw during finalization (69 failures).

packages/coding-agent/test/task/executor-soft-budget.test.ts

@@ -63,6 +63,7 @@ function createMockSession(
 	};
 
 	const session: Partial<AgentSession> = {
+		setIrcWakeTurnObserver: () => {},
 		state: { messages: [] } as never,
 		agent: { state: { systemPrompt: ["test"] } } as never,
 		model: { api: "anthropic-messages" } as never,