feat: add 2 new failure modes — rate limiting and streaming fallback

- Rate limiting during reconnection (429): honor retry-after headers
- Placeholder edit fails silently: fallback to sending as new message
- Both fixes deployed to pi Zulip extension

zulip-adapter-lessons.prose.md

@@ -57,6 +57,18 @@ description: >
 - **Fix**: Kill old process before starting, or use docker restart to clear state
 - **Applies to**: kagentz Agent Zero deployment
 
+### 9. Zulip API Rate Limiting During Reconnection
+- **Symptom**: Extension gets 429 errors and can't reconnect — responses vanish
+- **Root cause**: Rapid PM2 restarts cause multiple queue registrations, hitting Zulip's per-IP rate limit
+- **Fix**: Read `retry-after` header and wait before retrying; increase backoff between retries
+- **Applies to**: pi extension (fixed), Hermes adapter (has retry logic but should check retry-after)
+
+### 10. Placeholder Edit Fails Silently (Streaming Vanishes)
+- **Symptom**: User sees "Thinking..." placeholder but never gets the actual response
+- **Root cause**: `editMessage` API call fails (e.g., message too old, rate limited) but no fallback
+- **Fix**: If edit fails, send the response as a new message instead
+- **Applies to**: pi extension (fixed), Hermes adapter (verify edit fallback exists)
+
 ## Deployment Checklist
 
 When deploying a new Zulip adapter, verify: