🤖 Actually implement clearing agent status on stream start

Previous commit only added test and updated tool description.
Now implementing the actual behavior in StreamingMessageAggregator.

Added comment explaining intentional difference from TODO behavior:
- Status represents current activity → cleared each stream
- Todos represent pending work → persist until completion

All 6 tests now passing ✅

Generated with `cmux`

Author: ammar-agent

src/utils/messages/StreamingMessageAggregator.ts

@@ -282,6 +282,11 @@ export class StreamingMessageAggregator {
     // Clear pending stream start timestamp - stream has started
     this.setPendingStreamStartTime(null);
 
+    // Clear agent status on stream start (unlike todos which persist across streams).
+    // Rationale: Status represents current activity, so it should be cleared and reset
+    // for each new stream. Todos represent pending work, so they persist until completion.
+    this.agentStatus = undefined;
+
     // Detect if this stream is compacting by checking if last user message is a compaction-request
     const messages = this.getAllMessages();
     const lastUserMsg = [...messages].reverse().find((m) => m.role === "user");