fix(channels): harden runtime credential management APIs (#3581)

* fix(channels): harden runtime credential management APIs

* fix(channels): address review feedback on credential hardening

Follow-up to the runtime credential-hardening pass, resolving five review
findings:

- WeChat auth persistence now writes through a 0o600 NamedTemporaryFile +
  Path.replace instead of write_text-then-chmod, so the iLink bot_token is
  never briefly readable at umask defaults (mirrors ChannelRuntimeConfigStore).
- The post-write chmod is split into its own try/except: a chmod failure on a
  filesystem without POSIX perms now logs at debug instead of masquerading as
  a "failed to persist" warning.
- Extracted the three near-identical _require_admin_user helpers (mcp,
  channel_connections, channels) into a single require_admin_user(request, *,
  detail) in app/gateway/deps.py; each router supplies its own detail string.
- Strengthened the runtime-config-store chmod coverage: a new test injects a
  temp-file chmod failure and asserts it is logged at debug while the
  destination is still owner-only (mutation-verified to fail if the chmod is
  dropped), plus a loose-pre-existing-file case.
- Removed the unused _FakeRepo from the blocking-io test: its isinstance gate
  routes through the repo-less 503 path, so neither stub was ever invoked.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/app/gateway/routers/channel_connections.py

@@ -16,6 +16,7 @@ from app.channels.runtime_config_store import (
     apply_runtime_connection_config,
     merge_runtime_channel_configs,
 )
+from app.gateway.deps import require_admin_user
 from deerflow.config.channel_connections_config import ChannelConnectionsConfig
 from deerflow.persistence.channel_connections import ChannelConnectionRepository
 from deerflow.persistence.engine import get_session_factory
@@ -26,6 +27,7 @@ logger = logging.getLogger(__name__)
 _STATE_TTL_SECONDS = 600
 _MAX_PENDING_CONNECT_CODES_PER_PROVIDER = 5
 _MASKED_CREDENTIAL_VALUE = "********"
+_ADMIN_REQUIRED_DETAIL = "Admin privileges required to manage channel runtime credentials."
 
 
 class ChannelCredentialFieldResponse(BaseModel):
@@ -135,24 +137,6 @@ def _get_user_id(request: Request) -> str:
     return str(user.id)
 
 
-async def _require_admin_user(request: Request) -> None:
-    """Require an admin caller for instance-wide channel runtime mutations.
-
-    Runtime credentials and the channel workers they start/stop are shared by
-    every user of the deployment, so only admins may change them (same model
-    as the MCP config API). Auth-disabled local mode uses a synthetic admin
-    user and is unaffected.
-    """
-    user = getattr(request.state, "user", None)
-    if user is None:
-        from app.gateway.deps import get_current_user_from_request
-
-        user = await get_current_user_from_request(request)
-
-    if getattr(user, "system_role", None) != "admin":
-        raise HTTPException(status_code=403, detail="Admin privileges required to manage channel runtime credentials.")
-
-
 def _get_app_config():
     from deerflow.config.app_config import get_app_config
 
@@ -572,7 +556,7 @@ async def disconnect_channel_connection(connection_id: str, request: Request) ->
 
 @router.delete("/{provider}/runtime-config", response_model=ChannelProviderResponse)
 async def disconnect_channel_provider_runtime(provider: str, request: Request) -> ChannelProviderResponse:
-    await _require_admin_user(request)
+    await require_admin_user(request, detail=_ADMIN_REQUIRED_DETAIL)
     config = await _get_channel_connections_config(request)
     if not config.enabled:
         raise HTTPException(status_code=400, detail="Channel connections are disabled")
@@ -658,7 +642,7 @@ async def configure_channel_provider_runtime(
     body: ChannelRuntimeConfigRequest,
     request: Request,
 ) -> ChannelProviderResponse:
-    await _require_admin_user(request)
+    await require_admin_user(request, detail=_ADMIN_REQUIRED_DETAIL)
     config = await _get_channel_connections_config(request)
     if not config.enabled:
         raise HTTPException(status_code=400, detail="Channel connections are disabled")