refactor: thread app_config through middleware factories (#2652)

* refactor: thread app_config through middleware factories

Continues the incremental config-refactor sequence (#2611 root, #2612 lead
path) one layer deeper into the middleware factories. Two ambient lookups
inside _build_runtime_middlewares are eliminated and the LLMErrorHandling
band-aid removed:

- _build_runtime_middlewares / build_lead_runtime_middlewares /
  build_subagent_runtime_middlewares now require app_config: AppConfig.
- get_guardrails_config() inside the factory is replaced with
  app_config.guardrails (semantically identical — same default-factory
  GuardrailsConfig — verified by direct equality check).
- LLMErrorHandlingMiddleware.__init__ now requires app_config and reads
  circuit_breaker fields directly. The class-level
  circuit_failure_threshold / circuit_recovery_timeout_sec defaults are
  removed along with the try/except (FileNotFoundError, RuntimeError):
  pass band-aid — the let-it-crash invariant the rest of the refactor
  enforces.

Caller chain (already-resolved app_config sources):
- _build_middlewares in lead_agent/agent.py: reorder so
  resolved_app_config = app_config or get_app_config() is computed BEFORE
  build_lead_runtime_middlewares is called, then passed as kwarg.
- SubagentExecutor: optional app_config parameter (mirrors the lead-agent
  pattern); _create_agent does the same `or get_app_config()` fallback at
  agent-build time, so task_tool callers don't need to plumb app_config
  through yet (typed-context plumbing for tool runtimes is a separate
  refactor).

Tests:
- test_llm_error_handling_middleware: _make_app_config helper using
  AppConfig(sandbox=SandboxConfig(use="test")) — same minimal-config
  pattern conftest already uses. Three direct LLMErrorHandlingMiddleware()
  calls each followed by post-construction circuit_breaker mutation fold
  cleanly into _build_middleware(circuit_failure_threshold=...,
  circuit_recovery_timeout_sec=...).

Verification:
- tests/test_llm_error_handling_middleware.py — 14 passed
- tests/test_subagent_executor.py — 28 passed
- tests/test_tool_error_handling_middleware.py — 6 passed
- tests/test_task_tool_core_logic.py — 18 passed (verifies task_tool
  unchanged behavior)
- Full suite: 2697 passed, 3 skipped. The single intermittent failure in
  tests/test_client_e2e.py::test_tool_call_produces_events is pre-existing
  LLM flakiness (the test asserts the model decided to call a tool;
  reproduces 1/3 on unchanged main as well).

* fix: address middleware app config review comments

* fix: satisfy app config annotation lint

* test: cover explicit app config middleware wiring

---------

Co-authored-by: greatmengqi <chenmengqi.0376@bytedance.com>

backend/tests/test_tool_error_handling_middleware.py

@@ -1,10 +1,32 @@
-from types import SimpleNamespace
+import sys
+from types import ModuleType, SimpleNamespace
 
 import pytest
 from langchain_core.messages import ToolMessage
 from langgraph.errors import GraphInterrupt
 
-from deerflow.agents.middlewares.tool_error_handling_middleware import ToolErrorHandlingMiddleware
+from deerflow.agents.middlewares.tool_error_handling_middleware import (
+    ToolErrorHandlingMiddleware,
+    build_subagent_runtime_middlewares,
+)
+from deerflow.config.app_config import AppConfig, CircuitBreakerConfig
+from deerflow.config.guardrails_config import GuardrailsConfig
+from deerflow.config.sandbox_config import SandboxConfig
+
+
+def _module(name: str, **attrs):
+    module = ModuleType(name)
+    for key, value in attrs.items():
+        setattr(module, key, value)
+    return module
+
+
+def _make_app_config() -> AppConfig:
+    return AppConfig(
+        sandbox=SandboxConfig(use="test"),
+        guardrails=GuardrailsConfig(enabled=False),
+        circuit_breaker=CircuitBreakerConfig(failure_threshold=7, recovery_timeout_sec=11),
+    )
 
 
 def _request(name: str = "web_search", tool_call_id: str | None = "tc-1"):
@@ -14,6 +36,56 @@ def _request(name: str = "web_search", tool_call_id: str | None = "tc-1"):
     return SimpleNamespace(tool_call=tool_call)
 
 
+def test_build_subagent_runtime_middlewares_threads_app_config_to_llm_middleware(monkeypatch: pytest.MonkeyPatch):
+    captured: dict[str, object] = {}
+
+    class FakeMiddleware:
+        def __init__(self, *args, **kwargs):
+            self.args = args
+            self.kwargs = kwargs
+
+    class FakeLLMErrorHandlingMiddleware:
+        def __init__(self, *, app_config):
+            captured["app_config"] = app_config
+
+    app_config = _make_app_config()
+
+    monkeypatch.setitem(
+        sys.modules,
+        "deerflow.agents.middlewares.llm_error_handling_middleware",
+        _module(
+            "deerflow.agents.middlewares.llm_error_handling_middleware",
+            LLMErrorHandlingMiddleware=FakeLLMErrorHandlingMiddleware,
+        ),
+    )
+    monkeypatch.setitem(
+        sys.modules,
+        "deerflow.agents.middlewares.thread_data_middleware",
+        _module("deerflow.agents.middlewares.thread_data_middleware", ThreadDataMiddleware=FakeMiddleware),
+    )
+    monkeypatch.setitem(
+        sys.modules,
+        "deerflow.sandbox.middleware",
+        _module("deerflow.sandbox.middleware", SandboxMiddleware=FakeMiddleware),
+    )
+    monkeypatch.setitem(
+        sys.modules,
+        "deerflow.agents.middlewares.dangling_tool_call_middleware",
+        _module("deerflow.agents.middlewares.dangling_tool_call_middleware", DanglingToolCallMiddleware=FakeMiddleware),
+    )
+    monkeypatch.setitem(
+        sys.modules,
+        "deerflow.agents.middlewares.sandbox_audit_middleware",
+        _module("deerflow.agents.middlewares.sandbox_audit_middleware", SandboxAuditMiddleware=FakeMiddleware),
+    )
+
+    middlewares = build_subagent_runtime_middlewares(app_config=app_config, lazy_init=False)
+
+    assert captured["app_config"] is app_config
+    assert len(middlewares) == 6
+    assert isinstance(middlewares[-1], ToolErrorHandlingMiddleware)
+
+
 def test_wrap_tool_call_passthrough_on_success():
     middleware = ToolErrorHandlingMiddleware()
     req = _request()