Address review feedback on the previous commit:
1. Narrow exception catch removed. The old contract returned 503 whenever
`app.state.config is None`. The first cut only mapped
`FileNotFoundError`, leaving `PermissionError`, YAML parse errors, and
pydantic `ValidationError` to bubble up as 500. At the request boundary
we treat any inability to materialise the config as "configuration not
available" (503) and log the original exception so the operator still
has the stack.
2. Removed the unused `request: Request` parameter and the matching
`# noqa: ARG001`. FastAPI's `Depends()` does not require the dependency
to accept `Request`; the only call site uses the no-arg form.
3. `backend/CLAUDE.md` boundary now lists the *reason* each field is
restart-required (engine binding, singleton caching, one-shot
`apply_logging_level`, etc.), not just the field name, so reviewers do
not have to reverse-engineer the boundary themselves.
Tests parametrise four exception classes (`FileNotFoundError`,
`PermissionError`, `ValueError`, `RuntimeError`) and assert 503 for each.
Refs: bytedance/deer-flow#3107 (BUG-001)
`get_config(request)` returned the `app.state.config` snapshot captured at
startup. The worker / lead-agent path then threaded that frozen `AppConfig`
through `RunContext` and `agent_factory`, so per-run fields edited in
`config.yaml` (notably `max_tokens`) were ignored until the gateway process
was restarted — even though `get_app_config()` already does mtime-based
reload at the bottom layer.
Route the request dependency through `get_app_config()` directly. Runtime
`ContextVar` overrides (`push_current_app_config`) and test-injected
singletons (`set_app_config`) keep working; `app.state.config` is now only
read at startup for one-shot bootstrap (logging level, IM channels,
`langgraph_runtime` engines).
`tests/test_gateway_deps_config.py` encoded the old snapshot contract and is
removed; `tests/test_gateway_config_freshness.py` replaces it with mtime,
ContextVar, and `set_app_config` coverage. `test_skills_custom_router.py` and
`test_uploads_router.py` now inject test configs via FastAPI
`dependency_overrides[get_config]` instead of mutating `app.state.config`.
Document the hot-reload boundary in `backend/CLAUDE.md` so reviewers know
which fields are picked up on the next request vs. which still require a
restart (`database`, `checkpointer`, `run_events`, `stream_bridge`,
`sandbox.use`, `log_level`, `channels.*`).
Refs: bytedance/deer-flow#3107 (BUG-001)
fancyboi999