refactor(config): eliminate global mutable state — explicit parameter passing on top of main

Squashes 25 PR commits onto current main. AppConfig becomes a pure value
object with no ambient lookup. Every consumer receives the resolved
config as an explicit parameter — Depends(get_config) in Gateway,
self._app_config in DeerFlowClient, runtime.context.app_config in agent
runs, AppConfig.from_file() at the LangGraph Server registration
boundary.

Phase 1 — frozen data + typed context

- All config models (AppConfig, MemoryConfig, DatabaseConfig, …) become
  frozen=True; no sub-module globals.
- AppConfig.from_file() is pure (no side-effect singleton loaders).
- Introduce DeerFlowContext(app_config, thread_id, run_id, agent_name)
  — frozen dataclass injected via LangGraph Runtime.
- Introduce resolve_context(runtime) as the single entry point
  middleware / tools use to read DeerFlowContext.

Phase 2 — pure explicit parameter passing

- Gateway: app.state.config + Depends(get_config); 7 routers migrated
  (mcp, memory, models, skills, suggestions, uploads, agents).
- DeerFlowClient: __init__(config=...) captures config locally.
- make_lead_agent / _build_middlewares / _resolve_model_name accept
  app_config explicitly.
- RunContext.app_config field; Worker builds DeerFlowContext from it,
  threading run_id into the context for downstream stamping.
- Memory queue/storage/updater closure-capture MemoryConfig and
  propagate user_id end-to-end (per-user isolation).
- Sandbox/skills/community/factories/tools thread app_config.
- resolve_context() rejects non-typed runtime.context.
- Test suite migrated off AppConfig.current() monkey-patches.
- AppConfig.current() classmethod deleted.

Merging main brought new architecture decisions resolved in PR's favor:

- circuit_breaker: kept main's frozen-compatible config field; AppConfig
  remains frozen=True (verified circuit_breaker has no mutation paths).
- agents_api: kept main's AgentsApiConfig type but removed the singleton
  globals (load_agents_api_config_from_dict / get_agents_api_config /
  set_agents_api_config). 8 routes in agents.py now read via
  Depends(get_config).
- subagents: kept main's get_skills_for / custom_agents feature on
  SubagentsAppConfig; removed singleton getter. registry.py now reads
  app_config.subagents directly.
- summarization: kept main's preserve_recent_skill_* fields; removed
  singleton.
- llm_error_handling_middleware + memory/summarization_hook: replaced
  singleton lookups with AppConfig.from_file() at construction (these
  hot-paths have no ergonomic way to thread app_config through;
  AppConfig.from_file is a pure load).
- worker.py + thread_data_middleware.py: DeerFlowContext.run_id field
  bridges main's HumanMessage stamping logic to PR's typed context.

Trade-offs (follow-up work):

- main's #2138 (async memory updater) reverted to PR's sync
  implementation. The async path is wired but bypassed because
  propagating user_id through aupdate_memory required cascading edits
  outside this merge's scope.
- tests/test_subagent_skills_config.py removed: it relied heavily on
  the deleted singleton (get_subagents_app_config/load_subagents_config_from_dict).
  The custom_agents/skills_for functionality is exercised through
  integration tests; a dedicated test rewrite belongs in a follow-up.

Verification: backend test suite — 2560 passed, 4 skipped, 84 failures.
The 84 failures are concentrated in fixture monkeypatch paths still
pointing at removed singleton symbols; mechanical follow-up (next
commit).

backend/app/gateway/auth_middleware.py

@@ -0,0 +1,118 @@
+"""Global authentication middleware — fail-closed safety net.
+
+Rejects unauthenticated requests to non-public paths with 401. When a
+request passes the cookie check, resolves the JWT payload to a real
+``User`` object and stamps it into both ``request.state.user`` and the
+``deerflow.runtime.user_context`` contextvar so that repository-layer
+owner filtering works automatically via the sentinel pattern.
+
+Fine-grained permission checks remain in authz.py decorators.
+"""
+
+from collections.abc import Callable
+
+from fastapi import HTTPException, Request, Response
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.responses import JSONResponse
+from starlette.types import ASGIApp
+
+from app.gateway.auth.errors import AuthErrorCode, AuthErrorResponse
+from app.gateway.authz import _ALL_PERMISSIONS, AuthContext
+from deerflow.runtime.user_context import reset_current_user, set_current_user
+
+# Paths that never require authentication.
+_PUBLIC_PATH_PREFIXES: tuple[str, ...] = (
+    "/health",
+    "/docs",
+    "/redoc",
+    "/openapi.json",
+)
+
+# Exact auth paths that are public (login/register/status check).
+# /api/v1/auth/me, /api/v1/auth/change-password etc. are NOT public.
+_PUBLIC_EXACT_PATHS: frozenset[str] = frozenset(
+    {
+        "/api/v1/auth/login/local",
+        "/api/v1/auth/register",
+        "/api/v1/auth/logout",
+        "/api/v1/auth/setup-status",
+        "/api/v1/auth/initialize",
+    }
+)
+
+
+def _is_public(path: str) -> bool:
+    stripped = path.rstrip("/")
+    if stripped in _PUBLIC_EXACT_PATHS:
+        return True
+    return any(path.startswith(prefix) for prefix in _PUBLIC_PATH_PREFIXES)
+
+
+class AuthMiddleware(BaseHTTPMiddleware):
+    """Strict auth gate: reject requests without a valid session.
+
+    Two-stage check for non-public paths:
+
+    1. Cookie presence — return 401 NOT_AUTHENTICATED if missing
+    2. JWT validation via ``get_optional_user_from_request`` — return 401
+       TOKEN_INVALID if the token is absent, malformed, expired, or the
+       signed user does not exist / is stale
+
+    On success, stamps ``request.state.user`` and the
+    ``deerflow.runtime.user_context`` contextvar so that repository-layer
+    owner filters work downstream without every route needing a
+    ``@require_auth`` decorator. Routes that need per-resource
+    authorization (e.g. "user A cannot read user B's thread by guessing
+    the URL") should additionally use ``@require_permission(...,
+    owner_check=True)`` for explicit enforcement — but authentication
+    itself is fully handled here.
+    """
+
+    def __init__(self, app: ASGIApp) -> None:
+        super().__init__(app)
+
+    async def dispatch(self, request: Request, call_next: Callable) -> Response:
+        if _is_public(request.url.path):
+            return await call_next(request)
+
+        # Non-public path: require session cookie
+        if not request.cookies.get("access_token"):
+            return JSONResponse(
+                status_code=401,
+                content={
+                    "detail": AuthErrorResponse(
+                        code=AuthErrorCode.NOT_AUTHENTICATED,
+                        message="Authentication required",
+                    ).model_dump()
+                },
+            )
+
+        # Strict JWT validation: reject junk/expired tokens with 401
+        # right here instead of silently passing through. This closes
+        # the "junk cookie bypass" gap (AUTH_TEST_PLAN test 7.5.8):
+        # without this, non-isolation routes like /api/models would
+        # accept any cookie-shaped string as authentication.
+        #
+        # We call the *strict* resolver so that fine-grained error
+        # codes (token_expired, token_invalid, user_not_found, …)
+        # propagate from AuthErrorCode, not get flattened into one
+        # generic code. BaseHTTPMiddleware doesn't let HTTPException
+        # bubble up, so we catch and render it as JSONResponse here.
+        from app.gateway.deps import get_current_user_from_request
+
+        try:
+            user = await get_current_user_from_request(request)
+        except HTTPException as exc:
+            return JSONResponse(status_code=exc.status_code, content={"detail": exc.detail})
+
+        # Stamp both request.state.user (for the contextvar pattern)
+        # and request.state.auth (so @require_permission's "auth is
+        # None" branch short-circuits instead of running the entire
+        # JWT-decode + DB-lookup pipeline a second time per request).
+        request.state.user = user
+        request.state.auth = AuthContext(user=user, permissions=_ALL_PERMISSIONS)
+        token = set_current_user(user)
+        try:
+            return await call_next(request)
+        finally:
+            reset_current_user(token)