feat: zulip-adapter-lessons — document 8 known failure modes + deployment checklist

Documents lessons from building pi Zulip extension and Hermes Zulip plugin:
1. Queue registration content-type
2. Missing bot_user_id for @mentions
3. Zero stream subscriptions
4. Stale errors never cleared
5. Stuck detection too aggressive
6. Env var name mismatch
7. Poll interval too aggressive
8. A2A port conflict

Also: fixed Hermes adapter to clear stale errors on successful poll

zulip-adapter-lessons.prose.md

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+---
+kind: pattern
+name: zulip-adapter-lessons
+description: >
+  Lessons learned from building and debugging the pi Zulip extension and
+  Hermes Zulip plugin. Documents failure modes, fixes, and patterns that
+  apply across all Zulip adapters.
+---
+
+## Known Failure Modes & Fixes
+
+### 1. Queue Registration Content-Type
+- **Symptom**: Event queue registered but delivers no stream events
+- **Root cause**: `multipart/form-data` (from `isomorphic-form-data` / `form-data` npm pkgs) vs `application/x-www-form-urlencoded`
+- **Fix**: Always use URLSearchParams / form-urlencoded for `/api/v1/register`
+- **Applies to**: pi extension (fixed), Hermes adapter (httpx sends form-urlencoded by default ✅)
+
+### 2. Missing bot_user_id for @mention Detection
+- **Symptom**: Bot receives stream messages but doesn't respond to @mentions
+- **Root cause**: `/api/v1/register` doesn't return `user_id`; `mentioned_users` check fails when bot ID is null
+- **Fix**: Call `GET /api/v1/users/me` after registration to get `user_id`
+- **Applies to**: pi extension (fixed), Hermes adapter (fixed via `_resolve_bot_user_id()` ✅)
+
+### 3. Zero Stream Subscriptions
+- **Symptom**: Bot can send to streams but never receives stream events
+- **Root cause**: Bot user created with 0 stream subscriptions — only DMs arrive
+- **Fix**: `POST /api/v1/users/me/subscriptions` with required stream names
+- **Applies to**: pi extension (fixed), Hermes adapter (⚠️ needs check)
+
+### 4. Stale Errors Never Cleared
+- **Symptom**: Health monitor shows persistent error long after recovery
+- **Root cause**: `last_error` set on failure but never cleared on successful poll
+- **Fix**: Clear `lastError` on every successful poll (not just on reconnect)
+- **Applies to**: pi extension (fixed), Hermes adapter (⚠️ needs check)
+
+### 5. Stuck Detection Too Aggressive
+- **Symptom**: Monitor restarts bot during quiet periods (nights/weekends)
+- **Root cause**: 30-min stuck threshold doesn't account for low traffic
+- **Fix**: Raise threshold to 4 hours — or remove stuck detection entirely
+- **Applies to**: pi extension (fixed to 4h), Hermes gateway (uses own idle detection)
+
+### 6. Env Var Name Mismatch (ZULIP_URL vs ZULIP_SITE)
+- **Symptom**: Plugin not loading because check_fn returns False
+- **Root cause**: Some deploy configs use `ZULIP_URL`, adapter code expects `ZULIP_SITE`
+- **Fix**: Support both names in check_fn, validate_config, and env_enablement_fn
+- **Applies to**: Hermes adapter (fixed ✅)
+
+### 7. Poll Interval Too Aggressive
+- **Symptom**: Queue expires faster than expected, reconnection cycling
+- **Root cause**: 3s poll interval with `dont_block=true` creates many requests
+- **Fix**: Use long-poll (no `dont_block`) with 30s+ server timeout
+- **Applies to**: pi extension (uses long-poll ✅), Hermes adapter (uses long-poll ✅)
+
+### 8. A2A Server Address Already In Use
+- **Symptom**: A2A server fails to start with "[Errno 98] address already in use"
+- **Root cause**: Previous process holds port after container restart
+- **Fix**: Kill old process before starting, or use docker restart to clear state
+- **Applies to**: kagentz Agent Zero deployment
+
+## Deployment Checklist
+
+When deploying a new Zulip adapter, verify:
+
+- [ ] Queue registered with form-urlencoded content type
+- [ ] Bot user_id fetched from `/api/v1/users/me`
+- [ ] Subscribed to all expected streams (check with `/api/v1/users/me/subscriptions`)
+- [ ] `last_error` cleared on successful poll
+- [ ] Env vars support both `ZULIP_URL` and `ZULIP_SITE`
+- [ ] Stream @mentions detected via `mentioned_users` array
+- [ ] `@all-bots` detected via configurable user_id
+- [ ] Poll uses long-poll (not `dont_block=true` polling)
+- [ ] Stuck/idle detection accounts for quiet periods