fix(async): close unscheduled coroutines in all threadsafe bridges (#26584)

Wraps every sync->async coroutine-scheduling site in the codebase with a
new agent.async_utils.safe_schedule_threadsafe() helper that closes the
coroutine on scheduling failure (closed loop, shutdown race, etc.)
instead of leaking it as 'coroutine was never awaited' RuntimeWarnings
plus reference leaks.

22 production call sites migrated across the codebase:
- acp_adapter/events.py, acp_adapter/permissions.py
- agent/lsp/manager.py
- cron/scheduler.py (media + text delivery paths)
- gateway/platforms/feishu.py (5 sites, via existing _submit_on_loop helper
  which now delegates to safe_schedule_threadsafe)
- gateway/run.py (10 sites: telegram rename, agent:step hook, status
  callback, interim+bg-review, clarify send, exec-approval button+text,
  temp-bubble cleanup, channel-directory refresh)
- plugins/memory/hindsight, plugins/platforms/google_chat
- tools/browser_supervisor.py (3), browser_cdp_tool.py,
  computer_use/cua_backend.py, slash_confirm.py
- tools/environments/modal.py (_AsyncWorker)
- tools/mcp_tool.py (2 + 8 _run_on_mcp_loop callers converted to
  factory-style so the coroutine is never constructed on a dead loop)
- tui_gateway/ws.py

Tests: new tests/agent/test_async_utils.py covers helper behavior under
live loop, dead loop, None loop, and scheduling exceptions. Regression
tests added at three PR-original sites (acp events, acp permissions,
mcp loop runner) mirroring contributor's intent.

Live-tested end-to-end:
- Helper stress test: 1500 schedules across live/dead/race scenarios,
  zero leaked coroutines
- Race exercised: 5000 schedules with loop killed mid-flight, 100 ok /
  4900 None returns, zero leaks
- hermes chat -q with terminal tool call (exercises step_callback bridge)
- MCP probe against failing subprocess servers + factory path
- Real gateway daemon boot + SIGINT shutdown across multiple platform
  adapter inits
- WSTransport 100 live + 50 dead-loop writes
- Cron delivery path live + dead loop

Salvages PR #2657 — adopts contributor's intent over a much wider site
list and a single centralized helper instead of inline try/except at
each site. 3 of the original PR's 6 sites no longer exist on main
(environments/patches.py deleted, DingTalk refactored to native async);
the equivalent fix lives in tools/environments/modal.py instead.

Co-authored-by: JithendraNara <jithendranaidunara@gmail.com>

tests/agent/test_async_utils.py

@@ -0,0 +1,157 @@
+"""Tests for agent.async_utils.safe_schedule_threadsafe."""
+
+from __future__ import annotations
+
+import asyncio
+import gc
+import warnings
+from concurrent.futures import Future
+from unittest.mock import patch
+
+import pytest
+
+from agent.async_utils import safe_schedule_threadsafe
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _no_unawaited_warnings(caught, *, coro_name: str = "") -> bool:
+    """Return True if no "X was never awaited" warning slipped through.
+
+    When *coro_name* is provided, only warnings naming that coroutine are
+    counted — xdist workers may emit unrelated unawaited-coroutine warnings
+    (e.g. ``AsyncMockMixin._execute_mock_call``) from concurrent tests.
+    """
+    bad = [
+        w for w in caught
+        if issubclass(w.category, RuntimeWarning)
+        and "was never awaited" in str(w.message)
+        and (not coro_name or coro_name in str(w.message))
+    ]
+    return not bad
+
+
+# ---------------------------------------------------------------------------
+# Tests
+# ---------------------------------------------------------------------------
+
+class TestSafeScheduleThreadsafe:
+    def test_returns_future_on_success(self):
+        loop = asyncio.new_event_loop()
+        try:
+            import threading
+            ready = threading.Event()
+            stop = threading.Event()
+
+            def _runner():
+                asyncio.set_event_loop(loop)
+                ready.set()
+                loop.run_until_complete(_wait_for_stop(stop))
+
+            async def _wait_for_stop(ev):
+                while not ev.is_set():
+                    await asyncio.sleep(0.005)
+
+            t = threading.Thread(target=_runner, daemon=True)
+            t.start()
+            ready.wait(timeout=2)
+
+            async def _sample():
+                return 42
+
+            fut = safe_schedule_threadsafe(_sample(), loop)
+            assert isinstance(fut, Future)
+            assert fut.result(timeout=2) == 42
+
+            stop.set()
+            t.join(timeout=2)
+        finally:
+            if loop.is_running():
+                loop.call_soon_threadsafe(loop.stop)
+            loop.close()
+
+    def test_closed_loop_returns_none_and_closes_coroutine(self):
+        loop = asyncio.new_event_loop()
+        loop.close()
+
+        async def _sample():
+            return "ok"
+
+        coro = _sample()
+        with warnings.catch_warnings(record=True) as caught:
+            warnings.simplefilter("always")
+            result = safe_schedule_threadsafe(coro, loop)
+            del coro
+            gc.collect()
+
+        assert result is None
+        assert _no_unawaited_warnings(caught, coro_name='_sample')
+
+    def test_none_loop_returns_none_and_closes_coroutine(self):
+        async def _sample():
+            return "ok"
+
+        coro = _sample()
+        with warnings.catch_warnings(record=True) as caught:
+            warnings.simplefilter("always")
+            result = safe_schedule_threadsafe(coro, None)
+            del coro
+            gc.collect()
+
+        assert result is None
+        assert _no_unawaited_warnings(caught, coro_name='_sample')
+
+    def test_scheduling_exception_closes_coroutine(self):
+        """If run_coroutine_threadsafe raises, close the coroutine and return None."""
+        # A loop that *looks* open but raises on submission
+        loop = asyncio.new_event_loop()
+        try:
+            async def _sample():
+                return "ok"
+
+            coro = _sample()
+            with warnings.catch_warnings(record=True) as caught:
+                warnings.simplefilter("always")
+                with patch(
+                    "agent.async_utils.asyncio.run_coroutine_threadsafe",
+                    side_effect=RuntimeError("scheduler down"),
+                ):
+                    result = safe_schedule_threadsafe(coro, loop)
+                del coro
+                gc.collect()
+
+            assert result is None
+            assert _no_unawaited_warnings(caught, coro_name='_sample')
+        finally:
+            loop.close()
+
+    def test_logs_at_specified_level(self, caplog):
+        import logging
+        loop = asyncio.new_event_loop()
+        loop.close()
+
+        async def _sample():
+            return None
+
+        custom = logging.getLogger("test_async_utils")
+        with caplog.at_level(logging.WARNING, logger="test_async_utils"):
+            result = safe_schedule_threadsafe(
+                _sample(), loop,
+                logger=custom,
+                log_message="custom-msg",
+                log_level=logging.WARNING,
+            )
+
+        assert result is None
+        assert any("custom-msg" in rec.message for rec in caplog.records)
+
+    def test_non_coroutine_arg_does_not_crash(self):
+        """Defensive: even if the caller hands us something weird, don't blow up."""
+        loop = asyncio.new_event_loop()
+        loop.close()
+
+        # Pass a non-coroutine sentinel
+        result = safe_schedule_threadsafe("not-a-coroutine", loop)  # type: ignore[arg-type]
+        assert result is None