fix(coding-agent): drain follow-ups queued during agent_end

When an extension queues a follow-up during `agent_end` it
gets stuck on the follow-up queue until after the next user
message.

Add a hasQueuedMessages() check to _handlePostAgentRun
so the existing while/continue loop drains them.

- One-line fix in _handlePostAgentRun
- Integration test in agent-session-queue
- git-merge-and-resolve example extension with tests

packages/coding-agent/src/core/agent-session.ts

@@ -947,7 +947,13 @@ export class AgentSession {
 			this._retryAttempt = 0;
 		}
 
-		return await this._checkCompaction(msg);
+		if (await this._checkCompaction(msg)) {
+			return true;
+		}
+
+		// The agent loop drains both queues before emitting agent_end. Any messages
+		// here were queued by agent_end extension handlers and need a continuation.
+		return this.agent.hasQueuedMessages();
 	}
 
 	/**