Add configurable adapter selection to app runner

pm/tasks-v2.org

@@ -272,21 +272,23 @@ Build a simple Python orchestration layer in youdis.py so the standard app stack
    - leave room for future Zulip/XMPP adapters without redesigning the runner
 
 ** evidence
-- commit:
+- commit: 309ce87
 - tests:
   1. `python3 -m py_compile ./youdis.py ./youdis/adapters/discord.py`
   2. backend direct run still works: `python3 -m uvicorn youdis.main:app --host 127.0.0.1 --port 8000`
   3. discord direct run still works: `python3 -m youdis.adapters.discord`
-  4. app runner backend-only smoke test: `YOUDIS_RUN_DISCORD=0 timeout 5s python3 ./youdis.py`
+  4. app runner backend-only smoke test: `YOUDIS_ENABLED_ADAPTERS= timeout 5s python3 ./youdis.py`
   5. app runner default path: `python3 ./youdis.py`
-- date:
+- date: [2026-04-02 Thu 14:13]
 
 ** notes
 - `youdis.py` is now the default v2 app runner and starts the standard stack explicitly rather than dynamically discovering adapters
 - backend starts first and must pass a health check before the Discord adapter is launched
 - backend and Discord adapter remain directly runnable for debugging and tests
 - Docker is intended to invoke `python3 /app/youdis.py`; Python owns app orchestration while Docker owns packaging and runtime environment
-- runner flags currently include `YOUDIS_RUN_BACKEND`, `YOUDIS_RUN_DISCORD`, `YOUDIS_BACKEND_HOST`, and `YOUDIS_BACKEND_PORT`
+- adapter startup remains explicit in `youdis.py`, while `YOUDIS_ENABLED_ADAPTERS` selects which known adapters to run
+- adding an adapter means creating `youdis/adapters/<adapter>.py`, adding `start_<adapter>()` in `youdis.py`, registering it in the explicit adapter map, and documenting any env vars in `.env.example`
+- runner flags currently include `YOUDIS_RUN_BACKEND`, `YOUDIS_ENABLED_ADAPTERS`, `YOUDIS_BACKEND_HOST`, and `YOUDIS_BACKEND_PORT`
 
 
 * ==== BACKLOG ====