test: add blocking IO detector (#2924)

* test: add blocking IO detector

* test: add blocking IO probe option

* test: harden blocking IO probe lifecycle

* test: move blocking io detector to support

backend/tests/conftest.py

@@ -4,6 +4,8 @@ Sets up sys.path and pre-mocks modules that would cause circular import
 issues when unit-testing lightweight config/registry code in isolation.
 """
 
+from __future__ import annotations
+
 import importlib.util
 import sys
 from pathlib import Path
@@ -11,11 +13,16 @@ from types import SimpleNamespace
 from unittest.mock import MagicMock
 
 import pytest
+from support.detectors.blocking_io import BlockingIOProbe, detect_blocking_io
 
 # Make 'app' and 'deerflow' importable from any working directory
 sys.path.insert(0, str(Path(__file__).parent.parent))
 sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "scripts"))
 
+_BACKEND_ROOT = Path(__file__).resolve().parents[1]
+_blocking_io_probe = BlockingIOProbe(_BACKEND_ROOT)
+_BLOCKING_IO_DETECTOR_ATTR = "_blocking_io_detector"
+
 # Break the circular import chain that exists in production code:
 #   deerflow.subagents.__init__
 #     -> .executor (SubagentExecutor, SubagentResult)
@@ -56,6 +63,92 @@ def provisioner_module():
     return module
 
 
+@pytest.fixture()
+def blocking_io_detector():
+    """Fail a focused test if blocking calls run on the event loop thread."""
+    with detect_blocking_io(fail_on_exit=True) as detector:
+        yield detector
+
+
+def pytest_addoption(parser: pytest.Parser) -> None:
+    group = parser.getgroup("blocking-io")
+    group.addoption(
+        "--detect-blocking-io",
+        action="store_true",
+        default=False,
+        help="Collect blocking calls made while an asyncio event loop is running and report a summary.",
+    )
+    group.addoption(
+        "--detect-blocking-io-fail",
+        action="store_true",
+        default=False,
+        help="Set a failing exit status when --detect-blocking-io records violations.",
+    )
+
+
+def pytest_configure(config: pytest.Config) -> None:
+    config.addinivalue_line("markers", "no_blocking_io_probe: skip the optional blocking IO probe")
+
+
+def pytest_sessionstart(session: pytest.Session) -> None:
+    if _blocking_io_probe_enabled(session.config):
+        _blocking_io_probe.clear()
+
+
+@pytest.hookimpl(hookwrapper=True)
+def pytest_runtest_call(item: pytest.Item):
+    if not _blocking_io_probe_enabled(item.config) or _blocking_io_probe_skipped(item):
+        yield
+        return
+
+    detector = detect_blocking_io(fail_on_exit=False, stack_limit=18)
+    detector.__enter__()
+    setattr(item, _BLOCKING_IO_DETECTOR_ATTR, detector)
+    yield
+
+
+@pytest.hookimpl(hookwrapper=True)
+def pytest_runtest_teardown(item: pytest.Item):
+    yield
+
+    detector = getattr(item, _BLOCKING_IO_DETECTOR_ATTR, None)
+    if detector is None:
+        return
+
+    try:
+        detector.__exit__(None, None, None)
+        _blocking_io_probe.record(item.nodeid, detector.violations)
+    finally:
+        delattr(item, _BLOCKING_IO_DETECTOR_ATTR)
+
+
+def pytest_sessionfinish(session: pytest.Session) -> None:
+    if _blocking_io_fail_enabled(session.config) and _blocking_io_probe.violation_count and session.exitstatus == pytest.ExitCode.OK:
+        session.exitstatus = pytest.ExitCode.TESTS_FAILED
+
+
+def pytest_terminal_summary(terminalreporter: pytest.TerminalReporter) -> None:
+    if not _blocking_io_probe_enabled(terminalreporter.config):
+        return
+
+    header, *details = _blocking_io_probe.format_summary().splitlines()
+    terminalreporter.write_sep("=", header)
+    for line in details:
+        terminalreporter.write_line(line)
+
+
+def _blocking_io_probe_enabled(config: pytest.Config) -> bool:
+    return bool(config.getoption("--detect-blocking-io") or config.getoption("--detect-blocking-io-fail"))
+
+
+def _blocking_io_fail_enabled(config: pytest.Config) -> bool:
+    return bool(config.getoption("--detect-blocking-io-fail"))
+
+
+def _blocking_io_probe_skipped(item: pytest.Item) -> bool:
+    return item.path.name == "test_blocking_io_detector.py" or item.get_closest_marker("no_blocking_io_probe") is not None
+
+
 # ---------------------------------------------------------------------------
 # Auto-set user context for every test unless marked no_auto_user
 # ---------------------------------------------------------------------------