feat: per-user channel config for Google Chat and Nextcloud Talk

- New endpoints: POST /channels/google-chat/{username} and /webhook/nextcloud/{username}
- Channel secrets/config live in home/{username}/channels.json (gitignored)
- auth_utils: get_user_channels() helper reads channels.json
- Both routers load persona, audience/secret, backend, timeout per user;
  set_context() wires the correct persona before building the system prompt
- Removed server-level channel settings from config.py and .env —
  no user gets a channel until they create their own channels.json
- .gitignore: home/**/channels.json added

To migrate: update Google Chat Add-on webhook URL to /channels/google-chat/{username}
and re-register NC Talk bot at /webhook/nextcloud/{username}

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/routers/google_chat.py

@@ -3,14 +3,16 @@ import logging
 from fastapi import APIRouter, HTTPException, Request, Response
 from google.auth.transport import requests as google_requests
 from google.oauth2 import id_token
+from auth_utils import get_user_channels
 from context_loader import load_context
 from llm_client import complete
+from persona import set_context
 from session_logger import log_turn
 from session_store import load as load_session, save as save_session
 from config import settings
 
 logger = logging.getLogger(__name__)
-router = APIRouter(prefix="/channels/google-chat")
+router = APIRouter()
 
 # Workspace Add-on Chat apps: JWT is issued by accounts.google.com.
 # (Legacy standalone Chat bots used chat@system.gserviceaccount.com — different format.)
@@ -35,7 +37,7 @@ def _msg(text: str) -> dict:
     }
 
 
-def _verify_system_id_token(token: str) -> None:
+def _verify_system_id_token(token: str, audience: str) -> None:
     """Verify the systemIdToken from authorizationEventObject.
 
     For Workspace Add-on Chat apps Google sends the token in the request body
@@ -44,13 +46,13 @@ def _verify_system_id_token(token: str) -> None:
 
     Claims verified:
       iss  = "https://accounts.google.com"
-      aud  = settings.google_chat_audience (the endpoint URL)
+      aud  = the per-user audience from channels.json (the endpoint URL)
     """
     try:
         claims = id_token.verify_oauth2_token(
             token,
             google_requests.Request(),
-            audience=settings.google_chat_audience,
+            audience=audience,
         )
     except Exception as exc:
         logger.warning("Google Chat JWT verification failed: %s", exc)
@@ -60,17 +62,30 @@ def _verify_system_id_token(token: str) -> None:
         raise HTTPException(status_code=401, detail="Wrong issuer")
 
 
-@router.post("")
-async def receive(request: Request):
+@router.post("/channels/google-chat/{username}")
+async def receive(username: str, request: Request):
+    channels = get_user_channels(username)
+    cfg = channels.get("google_chat")
+    if not cfg:
+        logger.warning("Google Chat: no channel config for user %r", username)
+        raise HTTPException(status_code=404, detail="Channel not configured for this user")
+
+    persona_name = cfg.get("persona", "inara")
+    audience     = cfg.get("audience", "")
+    backend      = cfg.get("backend", settings.primary_backend)
+    timeout      = cfg.get("timeout", 25)
+
+    set_context(username, persona_name)
+
     body = await request.json()
 
     # Verify the systemIdToken embedded in the request body
-    if settings.google_chat_audience:
+    if audience:
         token = body.get("authorizationEventObject", {}).get("systemIdToken", "")
         if not token:
-            logger.warning("Google Chat: missing systemIdToken")
+            logger.warning("Google Chat: missing systemIdToken for %s", username)
             raise HTTPException(status_code=401, detail="Missing token")
-        _verify_system_id_token(token)
+        _verify_system_id_token(token, audience)
 
     chat = body.get("chat", {})
 
@@ -79,8 +94,8 @@ async def receive(request: Request):
     if "addedToSpacePayload" in chat:
         space_type = chat["addedToSpacePayload"].get("space", {}).get("type", "")
         if space_type == "DM":
-            return _msg(f"✨ Hello! I'm {settings.agent_name}. What can I help you with?")
-        return _msg(f"✨ Hello! I'm {settings.agent_name}. Send me a message and I'll do my best to help.")
+            return _msg(f"✨ Hello! I'm {persona_name.capitalize()}. What can I help you with?")
+        return _msg(f"✨ Hello! I'm {persona_name.capitalize()}. Send me a message and I'll do my best to help.")
 
     if "removedFromSpacePayload" in chat:
         return Response(status_code=200)
@@ -89,10 +104,10 @@ async def receive(request: Request):
         logger.info("Google Chat: unhandled event keys: %s", list(chat.keys()))
         return Response(status_code=200)
 
-    payload       = chat["messagePayload"]
-    message       = payload.get("message", {})
-    space         = payload.get("space", {})
-    user          = chat.get("user", {})
+    payload        = chat["messagePayload"]
+    message        = payload.get("message", {})
+    space          = payload.get("space", {})
+    user           = chat.get("user", {})
 
     # argumentText strips @BotName mentions in Spaces; fall back to full text in DMs
     user_text      = (message.get("argumentText") or message.get("text", "")).strip()
@@ -107,7 +122,7 @@ async def receive(request: Request):
         logger.warning("Google Chat: empty user_text, ignoring")
         return Response(status_code=200)
 
-    session_id    = "gc_" + space_name.replace("/", "_")
+    session_id    = f"gc_{username}_{space_name.replace('/', '_')}"
     system_prompt = load_context(settings.default_tier)
     history       = load_session(session_id)
     history.append({"role": "user", "content": user_text})
@@ -117,9 +132,9 @@ async def receive(request: Request):
             complete(
                 system_prompt=system_prompt,
                 messages=history,
-                model=settings.google_chat_backend,
+                model=backend,
             ),
-            timeout=settings.google_chat_timeout,
+            timeout=timeout,
         )
     except asyncio.TimeoutError:
         logger.warning("Google Chat request timed out for session %s", session_id)