fix(skills): offload blocking filesystem IO in get_custom_skill_history (#3563)

* fix(skills): offload blocking filesystem IO in get_custom_skill_history

The GET /api/skills/custom/{name}/history handler ran its storage probes and the
per-skill .history read directly on the asyncio event loop:
get_or_new_skill_storage(), custom_skill_exists(), get_skill_history_file().exists()
and read_history() are all blocking filesystem IO. make detect-blocking-io flagged
the existence probe (routers/skills.py:224) as DIRECT_ASYNC.

Move the whole read into a nested sync function run via asyncio.to_thread; a None
return signals 404 (distinct from an empty history list). Behavior is unchanged.

Per the blocking-io-guard SOP:
- Candidate: get_custom_skill_history (FILE_METADATA, DIRECT_ASYNC) -> FIX+ANCHOR.
- Re-scan: the finding no longer appears for this handler.
- Anchor: tests/blocking_io/test_skills_router.py drives the real handler against a
  real on-disk skill + history; teeth verified red (pre-fix) -> green (post-fix)
  under make test-blocking-io.

Scoped to this self-contained read handler. rollback_custom_skill and update_skill
also touch blocking IO but interleave it with awaits (security scan / cache refresh)
and do a read-modify-write, so offloading them needs the asyncio.Lock serialization
treatment (cf. #3552) and is left as a separate fix unit.

* test: trim dead skills history setup

* fix(skills): use the user-scoped storage accessor in the offloaded history read

The merge with main left the offloaded reader calling get_or_new_skill_storage,
which is not defined in this module (ruff F821), so lint failed and the handler
would raise NameError at runtime. Use _get_user_skill_storage(config) — the same
accessor every other handler in this router uses.

Also update the regression test for the current route signature: the handler is
now admin-only and takes a Request, so the test supplies request.state.user
(mirroring tests/blocking_io/test_channel_runtime_config_store.py) and seeds the
history through the same user-scoped accessor.

---------

Co-authored-by: ly-wang19 <ly-wang19@users.noreply.github.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/app/gateway/routers/skills.py

@@ -327,10 +327,20 @@ async def get_custom_skill_history(skill_name: str, request: Request, config: Ap
     await require_admin_user(request, detail=_ADMIN_REQUIRED_DETAIL)
     try:
         skill_name = skill_name.replace("\r\n", "").replace("\n", "")
-        storage = _get_user_skill_storage(config)
-        if not storage.custom_skill_exists(skill_name) and not storage.get_skill_history_file(skill_name).exists():
+
+        def _read_history() -> list[dict] | None:
+            # Worker thread: storage construction, the existence probes, and the
+            # history-file read are blocking filesystem IO that must stay off the
+            # event loop. None signals 404 to the caller.
+            storage = _get_user_skill_storage(config)
+            if not storage.custom_skill_exists(skill_name) and not storage.get_skill_history_file(skill_name).exists():
+                return None
+            return storage.read_history(skill_name)
+
+        history = await asyncio.to_thread(_read_history)
+        if history is None:
             raise HTTPException(status_code=404, detail=f"Custom skill '{skill_name}' not found")
-        return CustomSkillHistoryResponse(history=storage.read_history(skill_name))
+        return CustomSkillHistoryResponse(history=history)
     except HTTPException:
         raise
     except Exception as e:

backend/tests/blocking_io/test_skills_router.py

@@ -0,0 +1,65 @@
+"""Regression anchor: get_custom_skill_history must not block the event loop.
+
+``app.gateway.routers.skills.get_custom_skill_history`` is an async route handler
+that probes custom-skill storage (``custom_skill_exists`` /
+``get_skill_history_file().exists()``) and reads the per-skill ``.history`` file —
+all blocking filesystem IO. It offloads that work via ``asyncio.to_thread``; if it
+regresses back onto the event loop, the strict Blockbuster gate raises
+``BlockingError`` and this test fails.
+
+Seeding the history on disk is itself offloaded with ``asyncio.to_thread`` so only
+the handler's own filesystem access is exercised on the loop.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import json
+from pathlib import Path
+from types import SimpleNamespace
+from uuid import UUID
+
+import pytest
+from fastapi import Request
+
+from app.gateway.routers.skills import _get_user_skill_storage, get_custom_skill_history
+
+pytestmark = pytest.mark.asyncio
+
+
+def _config(skills_root: Path) -> SimpleNamespace:
+    return SimpleNamespace(
+        skills=SimpleNamespace(
+            get_skills_path=lambda: skills_root,
+            container_path="/mnt/skills",
+            use="deerflow.skills.storage.local_skill_storage:LocalSkillStorage",
+        )
+    )
+
+
+def _admin_request() -> Request:
+    # The route is admin-only. ``AuthMiddleware`` normally stamps
+    # ``request.state.user``; supply it directly here, as
+    # ``test_channel_runtime_config_store`` does for the same reason.
+    user = SimpleNamespace(id=UUID("11111111-2222-3333-4444-555555555555"), system_role="admin")
+    return Request({"type": "http", "headers": [], "state": {"user": user}})
+
+
+async def test_get_custom_skill_history_does_not_block_event_loop(tmp_path: Path) -> None:
+    config = _config(tmp_path / "skills")
+
+    def _seed() -> None:
+        # Seed through the same user-scoped accessor the handler uses so both
+        # resolve the same storage root. An existing history file is enough for
+        # the handler to skip the 404 branch and read it.
+        history_file = _get_user_skill_storage(config).get_skill_history_file("demo-skill")
+        history_file.parent.mkdir(parents=True, exist_ok=True)
+        history_file.write_text(json.dumps({"action": "human_edit", "new_content": "x"}) + "\n", encoding="utf-8")
+
+    request = await asyncio.to_thread(_admin_request)
+    await asyncio.to_thread(_seed)
+
+    response = await get_custom_skill_history("demo-skill", request, config)
+
+    assert len(response.history) == 1
+    assert response.history[-1]["action"] == "human_edit"