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/routers/runs.py

@@ -11,10 +11,11 @@ import asyncio
 import logging
 import uuid
 
-from fastapi import APIRouter, Request
+from fastapi import APIRouter, HTTPException, Query, Request
 from fastapi.responses import StreamingResponse
 
-from app.gateway.deps import get_checkpointer, get_run_manager, get_stream_bridge
+from app.gateway.authz import require_permission
+from app.gateway.deps import get_checkpointer, get_feedback_repo, get_run_event_store, get_run_manager, get_run_store, get_stream_bridge
 from app.gateway.routers.thread_runs import RunCreateRequest
 from app.gateway.services import sse_consumer, start_run
 from deerflow.runtime import serialize_channel_values
@@ -85,3 +86,57 @@ async def stateless_wait(body: RunCreateRequest, request: Request) -> dict:
         logger.exception("Failed to fetch final state for run %s", record.run_id)
 
     return {"status": record.status.value, "error": record.error}
+
+
+# ---------------------------------------------------------------------------
+# Run-scoped read endpoints
+# ---------------------------------------------------------------------------
+
+
+async def _resolve_run(run_id: str, request: Request) -> dict:
+    """Fetch run by run_id with user ownership check. Raises 404 if not found."""
+    run_store = get_run_store(request)
+    record = await run_store.get(run_id)  # user_id=AUTO filters by contextvar
+    if record is None:
+        raise HTTPException(status_code=404, detail=f"Run {run_id} not found")
+    return record
+
+
+@router.get("/{run_id}/messages")
+@require_permission("runs", "read")
+async def run_messages(
+    run_id: str,
+    request: Request,
+    limit: int = Query(default=50, le=200, ge=1),
+    before_seq: int | None = Query(default=None),
+    after_seq: int | None = Query(default=None),
+) -> dict:
+    """Return paginated messages for a run (cursor-based).
+
+    Pagination:
+    - after_seq: messages with seq > after_seq (forward)
+    - before_seq: messages with seq < before_seq (backward)
+    - neither: latest messages
+
+    Response: { data: [...], has_more: bool }
+    """
+    run = await _resolve_run(run_id, request)
+    event_store = get_run_event_store(request)
+    rows = await event_store.list_messages_by_run(
+        run["thread_id"], run_id,
+        limit=limit + 1,
+        before_seq=before_seq,
+        after_seq=after_seq,
+    )
+    has_more = len(rows) > limit
+    data = rows[:limit] if has_more else rows
+    return {"data": data, "has_more": has_more}
+
+
+@router.get("/{run_id}/feedback")
+@require_permission("runs", "read")
+async def run_feedback(run_id: str, request: Request) -> list[dict]:
+    """Return all feedback for a run."""
+    run = await _resolve_run(run_id, request)
+    feedback_repo = get_feedback_repo(request)
+    return await feedback_repo.list_by_run(run["thread_id"], run_id)