fix(acp): preserve usage and terminal evidence on timeout

src/benchflow/acp/runtime.py

@@ -26,6 +26,10 @@
 from benchflow.acp.client import ACPClient
 from benchflow.acp.container_transport import ContainerTransport
 from benchflow.acp.selection import selected_acp_transport
+from benchflow.acp.timeout_cleanup import (
+    cancel_and_drain_prompt_task,
+    cancel_prompt_after_timeout,
+)
 from benchflow.acp.types import McpServerSpec
 from benchflow.acp.watchdog import IdleWatchdog
 from benchflow.agents.protocol import ACPSessionAdapter
@@ -65,7 +69,6 @@
 
 _ACP_CONNECT_MAX_RETRIES = 3
 _ACP_CONNECT_BASE_DELAY = 2.0
-_PROMPT_CANCEL_DRAIN_TIMEOUT_SEC = 0.25
 _ACP_HANDSHAKE_TIMEOUT_ENV = "BENCHFLOW_ACP_HANDSHAKE_TIMEOUT"
 _ACP_HANDSHAKE_TIMEOUT_DEFAULT_SEC = 60.0
 _OPENHANDS_DISABLE_SUBAGENTS_ENV = "BENCHFLOW_OPENHANDS_DISABLE_SUBAGENTS"
@@ -744,31 +747,6 @@ async def execute_prompts(
     return trajectory, len(session.tool_calls)
 
 
-async def _cancel_and_drain_prompt_task(prompt_task: asyncio.Task) -> bool:
-    if prompt_task.done():
-        return True
-    prompt_task.cancel()
-    done, _pending = await asyncio.wait(
-        {prompt_task}, timeout=_PROMPT_CANCEL_DRAIN_TIMEOUT_SEC
-    )
-    if done:
-        with contextlib.suppress(BaseException):
-            prompt_task.result()
-        return True
-
-    logger.warning(
-        "ACP prompt task did not finish within %.2fs after cancellation",
-        _PROMPT_CANCEL_DRAIN_TIMEOUT_SEC,
-    )
-
-    def _consume_prompt_result(task: asyncio.Task) -> None:
-        with contextlib.suppress(BaseException):
-            task.result()
-
-    prompt_task.add_done_callback(_consume_prompt_result)
-    return False
-
-
 def _agent_prompt_timeout_error(session, timeout: int) -> AgentPromptTimeoutError:
     session.mark_prompt_end()
     pending_tool_call_ids = session.pending_tool_call_ids()
@@ -800,16 +778,19 @@ async def _prompt_with_wall_clock_budget(
 ):
     """Run a prompt until either it finishes or BenchFlow's budget expires."""
     prompt_task = asyncio.create_task(acp_client.prompt(prompt))
+    cleanup_attempted = False
     try:
         done, _pending = await asyncio.wait({prompt_task}, timeout=timeout)
         if done:
             return prompt_task.result()
-        if await _cancel_and_drain_prompt_task(prompt_task):
+        cleanup_attempted = True
+        if await cancel_prompt_after_timeout(acp_client, prompt_task):
             raise _agent_prompt_timeout_error(session, timeout)
         raise TimeoutError(f"Agent prompt exceeded wall-clock budget {timeout}s")
     finally:
-        if not prompt_task.done():
-            await _cancel_and_drain_prompt_task(prompt_task)
+        if not prompt_task.done() and not cleanup_attempted:
+            cleanup_attempted = True
+            await cancel_and_drain_prompt_task(prompt_task)
 
 
 async def _prompt_with_idle_watchdog(
@@ -821,6 +802,7 @@ async def _prompt_with_idle_watchdog(
 ):
     """Run one ACP prompt with wall-clock and idle-watchdog budgets."""
     prompt_task = asyncio.create_task(acp_client.prompt(prompt))
+    cleanup_attempted = False
     loop = asyncio.get_running_loop()
     watchdog = IdleWatchdog.start(
         session,
@@ -840,9 +822,13 @@ async def _prompt_with_idle_watchdog(
             now = loop.time()
             watchdog.observe(session, now=now)
             if watchdog.idle_expired(now):
-                raise watchdog.timeout_error(session, now=now)
+                error = watchdog.timeout_error(session, now=now)
+                cleanup_attempted = True
+                await cancel_prompt_after_timeout(acp_client, prompt_task)
+                raise error
             if watchdog.wall_clock_expired(now):
-                if await _cancel_and_drain_prompt_task(prompt_task):
+                cleanup_attempted = True
+                if await cancel_prompt_after_timeout(acp_client, prompt_task):
                     raise _agent_prompt_timeout_error(session, timeout)
                 raise TimeoutError(
                     f"Agent prompt exceeded wall-clock budget {timeout}s"
@@ -854,5 +840,6 @@ async def _prompt_with_idle_watchdog(
         # external-cancellation path (CancelledError from sleep). Bound the
         # drain so a non-cooperative Daytona/ACP read cannot hide the watchdog
         # timeout forever; cleanup will tear down the live process.
-        if not prompt_task.done():
-            await _cancel_and_drain_prompt_task(prompt_task)
+        if not prompt_task.done() and not cleanup_attempted:
+            cleanup_attempted = True
+            await cancel_and_drain_prompt_task(prompt_task)

src/benchflow/acp/timeout_cleanup.py

@@ -0,0 +1,90 @@
+"""Bounded cooperative cleanup for timed-out ACP prompts.
+
+The original prompt task remains the sole ACP response reader. A best-effort
+``session/cancel`` request runs independently while the prompt gets a short
+grace period to receive peer-authored terminal usage and tool updates. At the
+shared deadline, every surviving task is cancelled and boundedly drained.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import contextlib
+import logging
+from typing import Any
+
+logger = logging.getLogger(__name__)
+
+PROMPT_TIMEOUT_CLEANUP_TOTAL_SEC = 5.0
+PROMPT_CANCEL_DRAIN_TIMEOUT_SEC = 0.25
+
+
+def _consume_task_result(task: asyncio.Task) -> None:
+    with contextlib.suppress(BaseException):
+        task.result()
+
+
+async def _cancel_and_drain_tasks(tasks: set[asyncio.Task], timeout: float) -> None:
+    pending = {task for task in tasks if not task.done()}
+    for task in pending:
+        task.cancel()
+    _done, pending = (
+        await asyncio.wait(pending, timeout=timeout) if pending else (set(), set())
+    )
+    for task in tasks - pending:
+        _consume_task_result(task)
+    for task in pending:
+        task.add_done_callback(_consume_task_result)
+
+
+async def cancel_and_drain_prompt_task(prompt_task: asyncio.Task) -> bool:
+    """Hard-cancel a prompt and return whether it completed within the drain."""
+    if prompt_task.done():
+        _consume_task_result(prompt_task)
+        return True
+    await _cancel_and_drain_tasks({prompt_task}, PROMPT_CANCEL_DRAIN_TIMEOUT_SEC)
+    if prompt_task.done():
+        return True
+
+    logger.warning(
+        "ACP prompt task did not finish within %.2fs after cancellation",
+        PROMPT_CANCEL_DRAIN_TIMEOUT_SEC,
+    )
+    return False
+
+
+async def cancel_prompt_after_timeout(
+    acp_client: Any, prompt_task: asyncio.Task
+) -> bool:
+    """Request peer cancellation, then bound cleanup without adding a reader."""
+    cancel = getattr(acp_client, "cancel", None)
+    if not callable(cancel):
+        return await cancel_and_drain_prompt_task(prompt_task)
+    if prompt_task.done():
+        _consume_task_result(prompt_task)
+        return True
+
+    async def _request_cancel() -> None:
+        try:
+            await cancel()
+        except asyncio.CancelledError:
+            raise
+        except Exception:
+            logger.warning("Failed to request ACP prompt cancellation", exc_info=True)
+
+    loop = asyncio.get_running_loop()
+    deadline = loop.time() + PROMPT_TIMEOUT_CLEANUP_TOTAL_SEC
+    cancel_task = asyncio.create_task(_request_cancel())
+    try:
+        cooperative_timeout = max(
+            0.0,
+            deadline - loop.time() - PROMPT_CANCEL_DRAIN_TIMEOUT_SEC,
+        )
+        await asyncio.wait({prompt_task}, timeout=cooperative_timeout)
+    finally:
+        remaining = max(0.0, deadline - loop.time())
+        await _cancel_and_drain_tasks(
+            {prompt_task, cancel_task},
+            min(PROMPT_CANCEL_DRAIN_TIMEOUT_SEC, remaining),
+        )
+    return prompt_task.done()

src/benchflow/rollout/__init__.py

@@ -1371,6 +1371,9 @@ async def disconnect(self) -> None:
             self._capture_partial_session_factory_trajectory()
         else:
             self._capture_partial_acp_trajectory()
+        collect_native_usage = getattr(self, "_collect_native_acp_usage", None)
+        if callable(collect_native_usage):
+            collect_native_usage()
         if self._acp_client:
             try:
                 await self._acp_client.close()
@@ -2385,6 +2388,7 @@ async def connect_as(self, role: Role) -> None:
                     role.agent, getattr(self, "_task", None), agent_cfg
                 ),
             )
+        self._native_usage_checkpoint = None
         self._reapply_ask_user_handler()
         self._attach_trajectory_writer(rollout_dir)
         self._active_role = role

tests/test_acp.py

@@ -830,74 +830,6 @@ async def test_prompt_with_interleaved_notifications_and_request(self) -> None:
             await client.close()
 
 
-class TestACPIdleWatchdog:
-    @pytest.mark.asyncio
-    async def test_idle_watchdog_returns_even_when_prompt_cancel_drain_stalls(
-        self,
-    ) -> None:
-        """Guards the 2026-05-22 Daytona/Gemini blocker fix against stuck cancel drain.
-
-        When the idle watchdog fires it cancels the prompt task and drains it.
-        A non-cooperative agent — here one that swallows the cancellation and
-        blocks on an event that never arrives — must not be able to wedge the
-        watchdog: it bounds the drain and raises ``IdleTimeoutError`` anyway.
-
-        Determinism: this asserts the *behaviour* (idle error raised; the stuck
-        prompt task abandoned while still pending) rather than a wall-clock upper
-        bound, so it cannot be squeezed into a spurious failure when the full
-        suite loads the event loop. The outer ``wait_for`` is only a hang guard;
-        its timeout is deliberately loose (far above the real ~1.25s runtime), so
-        load can never trip it, while a regression to an unbounded drain hangs
-        past it and fails.
-        """
-        from benchflow.acp.runtime import IdleTimeoutError, execute_prompts
-
-        # release is never set while the watchdog runs, so the prompt task stays
-        # wedged in its cancellation handler — exactly the stuck-drain scenario.
-        class StubbornPromptClient:
-            def __init__(self) -> None:
-                self.release = asyncio.Event()
-                self.task: asyncio.Task | None = None
-
-            async def prompt(self, _prompt: str):
-                self.task = asyncio.current_task()
-                try:
-                    await asyncio.Future()
-                except asyncio.CancelledError:
-                    await self.release.wait()
-                    raise
-
-        client = StubbornPromptClient()
-        session = ACPSession("idle-session")
-
-        # Loose hang guard: ~4x the real runtime (1s idle detect + 0.25s bounded
-        # drain). Not a tight assertion — it only catches a true hang/regression.
-        hang_guard_sec = 5.0
-
-        try:
-            with pytest.raises(IdleTimeoutError, match="Agent idle for 1s"):
-                await asyncio.wait_for(
-                    execute_prompts(
-                        client,  # type: ignore[arg-type]
-                        session,
-                        ["solve"],
-                        timeout=30,
-                        idle_timeout=1,
-                    ),
-                    timeout=hang_guard_sec,
-                )
-            # The watchdog returned while the stuck prompt task is still wedged on
-            # release.wait(): proves it bounded the drain instead of waiting for a
-            # cancellation that never completes. Load-independent — no clock math.
-            assert client.task is not None
-            assert not client.task.done()
-        finally:
-            client.release.set()
-            if client.task is not None:
-                with pytest.raises(asyncio.CancelledError):
-                    await client.task
-
-
 class TestPendingToolCallGrace:
     @pytest.mark.asyncio
     async def test_lost_tool_call_completion_trips_idle_after_grace(self):