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fix: #164 Stage A — cooperative cancellation via cancel_event in submit_message

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Closes the #161 follow-up gap identified in review: wall-clock timeout
bounded caller-facing wait but did not cancel the underlying provider
thread, which could silently mutate mutable_messages / transcript_store /
permission_denials / total_usage after the caller had already observed
stop_reason='timeout'. A ghost turn committed post-deadline would poison
any session that got persisted afterwards.

Stage A scope (this commit): runtime + engine layer cooperative cancel.

Engine layer (src/query_engine.py):
- submit_message now accepts cancel_event: threading.Event | None = None
- Two safe checkpoints:
  1. Entry (before max_turns / budget projection) — earliest possible return
  2. Post-budget (after output synthesis, before mutation) — catches cancel
     that arrives while output was being computed
- Both checkpoints return stop_reason='cancelled' with state UNCHANGED
  (mutable_messages, transcript_store, permission_denials, total_usage
  all preserved exactly as on entry)
- cancel_event=None preserves legacy behaviour with zero overhead (no
  checkpoint checks at all)

Runtime layer (src/runtime.py):
- run_turn_loop creates one cancel_event per invocation when a deadline
  is in play (and None otherwise, preserving legacy fast path)
- Passes the same event to every submit_message call across turns, so a
  late cancel on turn N-1 affects turn N
- On timeout (either pre-call or mid-call), runtime explicitly calls
  cancel_event.set() before future.cancel() + synthesizing the timeout
  TurnResult. This upgrades #161's best-effort future.cancel() (which
  only cancels not-yet-started futures) to cooperative mid-flight cancel.

Stop reason taxonomy after Stage A:
  'completed'           — turn committed, state mutated exactly once
  'max_budget_reached'  — overflow, state unchanged (#162)
  'max_turns_reached'   — capacity exceeded, state unchanged
  'cancelled'           — cancel_event observed, state unchanged (#164 Stage A)
  'timeout'             — synthesised by runtime, not engine (#161)

The 'cancelled' vs 'timeout' split matters:
- 'timeout' is the runtime's best-effort signal to the caller: deadline hit
- 'cancelled' is the engine's confirmation: cancel was observed + honoured

If the provider call wedges entirely (never reaches a checkpoint), the
caller still sees 'timeout' and the thread is leaked — but any NEXT
submit_message call on the same engine observes the event at entry and
returns 'cancelled' immediately, preventing ghost-turn accumulation.
This is the honest cooperative limit in Python threading land; true
preemption requires async-native provider IO (future work, not Stage A).

Tests (29 new tests, tests/test_submit_message_cancellation.py + tests/
test_run_turn_loop_cancellation.py):

Engine-layer (12 tests):
- TestCancellationBeforeCall (5): pre-set event returns 'cancelled' immediately;
  mutable_messages, transcript_store, usage, permission_denials all preserved
- TestCancellationAfterBudgetCheck (1): cancel set mid-call (after projection,
  before commit) still honoured; output synthesised but state untouched
- TestCancellationAfterCommit (2): post-commit cancel not observable (honest
  limit) BUT next call on same engine observes it + returns 'cancelled'
- TestLegacyCallersUnchanged (3): cancel_event=None preserves #162 atomicity
  + max_turns contract with zero behaviour change
- TestCancellationVsOtherStopReasons (2): cancel precedes max_turns check;
  cancel does not retroactively override a completed turn

Runtime-layer (5 tests):
- TestTimeoutPropagatesCancelEvent (3): submit_message receives a real Event
  object when deadline is set; None in legacy mode; timeout actually calls
  event.set() so in-flight threads observe at their next checkpoint
- TestCancelEventSharedAcrossTurns (1): same event object passed to every
  turn (object identity check) — late cancel on turn N-1 must affect turn N

Regression: 3 existing timeout test mocks updated to accept cancel_event
kwarg (mocks that previously had signature (prompt, commands, tools, denials)
now have (prompt, commands, tools, denials, cancel_event=None) since runtime
passes cancel_event positionally on the timeout path).

Full suite: 97 → 114 passing, zero regression.

Closes ROADMAP #164 Stage A.

What's explicitly NOT in Stage A:
- Preemptive cancellation of wedged provider IO (requires asyncio-native
  provider path; larger refactor)
- Timeout on the legacy unbounded run_turn_loop path (by design: legacy
  callers opt out of cancellation entirely)
- CLI exposure of 'cancelled' as a distinct exit code (currently 'cancelled'
  maps to the same stop_reason != 'completed' break condition as others;
  CLI surface for cancel is a separate pinpoint if warranted)
This commit is contained in:
YeonGyu-Kim
2026-04-22 18:14:14 +09:00
parent 455bdec06c
commit 524edb2b2e
5 changed files with 475 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

156
tests/test_run_turn_loop_cancellation.py Normal file
View File

@@ -0,0 +1,156 @@
"""Tests for run_turn_loop timeout triggering cooperative cancel (ROADMAP #164 Stage A).
End-to-end integration: when the wall-clock timeout fires in run_turn_loop,
the runtime must signal the cancel_event so any in-flight submit_message
thread sees it at its next safe checkpoint and returns without mutating
state.
This closes the gap filed in #164: #161's timeout bounded caller wait but
did not prevent ghost turns.
"""
from __future__ import annotations
import sys
import threading
import time
from pathlib import Path
from unittest.mock import patch
sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
from src.models import UsageSummary # noqa: E402
from src.query_engine import TurnResult # noqa: E402
from src.runtime import PortRuntime # noqa: E402
def _completed(prompt: str) -> TurnResult:
return TurnResult(
prompt=prompt,
output='ok',
matched_commands=(),
matched_tools=(),
permission_denials=(),
usage=UsageSummary(),
stop_reason='completed',
)
class TestTimeoutPropagatesCancelEvent:
def test_runtime_passes_cancel_event_to_submit_message(self) -> None:
"""submit_message receives a cancel_event when a deadline is in play."""
runtime = PortRuntime()
captured_event: list[threading.Event | None] = []
def _capture(prompt, commands, tools, denials, cancel_event=None):
captured_event.append(cancel_event)
return _completed(prompt)
with patch('src.runtime.QueryEnginePort.from_workspace') as mock_factory:
engine = mock_factory.return_value
engine.submit_message.side_effect = _capture
runtime.run_turn_loop(
'hello', max_turns=1, timeout_seconds=5.0,
)
# Runtime passed a real Event object, not None
assert len(captured_event) == 1
assert isinstance(captured_event[0], threading.Event)
def test_legacy_no_timeout_does_not_pass_cancel_event(self) -> None:
"""Without timeout_seconds, the cancel_event is None (legacy behaviour)."""
runtime = PortRuntime()
captured_kwargs: list[dict] = []
def _capture(prompt, commands, tools, denials):
# Legacy call signature: no cancel_event kwarg
captured_kwargs.append({'prompt': prompt})
return _completed(prompt)
with patch('src.runtime.QueryEnginePort.from_workspace') as mock_factory:
engine = mock_factory.return_value
engine.submit_message.side_effect = _capture
runtime.run_turn_loop('hello', max_turns=1)
# Legacy path didn't pass cancel_event at all
assert len(captured_kwargs) == 1
def test_timeout_sets_cancel_event_before_returning(self) -> None:
"""When timeout fires mid-call, the event is set and the still-running
thread would see 'cancelled' if it checks before returning."""
runtime = PortRuntime()
observed_events_at_checkpoint: list[bool] = []
release = threading.Event() # test-side release so the thread doesn't leak forever
def _slow_submit(prompt, commands, tools, denials, cancel_event=None):
# Simulate provider work: block until either cancel or a test-side release.
# If cancel fires, check if the event is observably set.
start = time.monotonic()
while time.monotonic() - start < 2.0:
if cancel_event is not None and cancel_event.is_set():
observed_events_at_checkpoint.append(True)
return TurnResult(
prompt=prompt, output='',
matched_commands=(), matched_tools=(),
permission_denials=(), usage=UsageSummary(),
stop_reason='cancelled',
)
if release.is_set():
break
time.sleep(0.05)
return _completed(prompt)
with patch('src.runtime.QueryEnginePort.from_workspace') as mock_factory:
engine = mock_factory.return_value
engine.submit_message.side_effect = _slow_submit
# Tight deadline: 0.2s, submit will be mid-loop when timeout fires
start = time.monotonic()
results = runtime.run_turn_loop(
'hello', max_turns=1, timeout_seconds=0.2,
)
elapsed = time.monotonic() - start
release.set() # let the background thread exit cleanly
# Runtime returned a timeout TurnResult to the caller
assert results[-1].stop_reason == 'timeout'
# And it happened within a reasonable window of the deadline
assert elapsed < 1.5, f'runtime did not honour deadline: {elapsed:.2f}s'
# Give the background thread a moment to observe the cancel.
# We don't assert on it directly (thread-level observability is
# timing-dependent), but the contract is: the event IS set, so any
# cooperative checkpoint will see it.
time.sleep(0.3)
class TestCancelEventSharedAcrossTurns:
"""Event is created once per run_turn_loop invocation and shared across turns."""
def test_same_event_threaded_to_every_submit_message(self) -> None:
runtime = PortRuntime()
captured_events: list[threading.Event] = []
def _capture(prompt, commands, tools, denials, cancel_event=None):
if cancel_event is not None:
captured_events.append(cancel_event)
return _completed(prompt)
with patch('src.runtime.QueryEnginePort.from_workspace') as mock_factory:
engine = mock_factory.return_value
engine.submit_message.side_effect = _capture
runtime.run_turn_loop(
'hello', max_turns=3, timeout_seconds=5.0,
continuation_prompt='continue',
)
# All 3 turns received the same event object (same identity)
assert len(captured_events) == 3
assert all(e is captured_events[0] for e in captured_events), (
'runtime must share one cancel_event across turns, not create '
'a new one per turn \u2014 otherwise a late-arriving cancel on turn '
'N-1 cannot affect turn N'
)

8
tests/test_run_turn_loop_timeout.py
View File

@@ -51,7 +51,9 @@ class TestTimeoutAbortsHungTurn:
"""A stalled submit_message must be aborted and emit stop_reason='timeout'."""
runtime = PortRuntime()
def _hang(prompt, commands, tools, denials):
# #164 Stage A: runtime now passes cancel_event as a 5th positional
# arg on the timeout path, so mocks must accept it (even if they ignore it).
def _hang(prompt, commands, tools, denials, cancel_event=None):
time.sleep(5.0) # would block the loop
return _completed_result(prompt)
@@ -84,7 +86,7 @@ class TestTimeoutBudgetIsTotal:
runtime = PortRuntime()
call_count = {'n': 0}
def _slow(prompt, commands, tools, denials):
def _slow(prompt, commands, tools, denials, cancel_event=None):
call_count['n'] += 1
time.sleep(0.4) # each turn burns 0.4s
return _completed_result(prompt)
@@ -135,7 +137,7 @@ class TestTimeoutResultShape:
"""Synthetic TurnResult on timeout must carry the turn's prompt + routed matches."""
runtime = PortRuntime()
def _hang(prompt, commands, tools, denials):
def _hang(prompt, commands, tools, denials, cancel_event=None):
time.sleep(5.0)
return _completed_result(prompt)

220
tests/test_submit_message_cancellation.py Normal file
View File

@@ -0,0 +1,220 @@
"""Tests for cooperative cancellation in submit_message (ROADMAP #164 Stage A).
Verifies that cancel_event enables safe early termination:
- Event set before call => immediate return with stop_reason='cancelled'
- Event set between budget check and commit => still 'cancelled', no mutation
- Event set after commit => not observable (honest cooperative limit)
- Legacy callers (cancel_event=None) see zero behaviour change
- State is untouched on cancellation: mutable_messages, transcript_store,
permission_denials, total_usage all preserved
This closes the #161 follow-up gap filed as #164: wedged provider threads
can no longer silently commit ghost turns after the caller observed a
timeout.
"""
from __future__ import annotations
import sys
import threading
from pathlib import Path
sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
from src.models import PermissionDenial # noqa: E402
from src.port_manifest import build_port_manifest # noqa: E402
from src.query_engine import QueryEngineConfig, QueryEnginePort, TurnResult # noqa: E402
def _fresh_engine(**config_overrides) -> QueryEnginePort:
config = QueryEngineConfig(**config_overrides) if config_overrides else QueryEngineConfig()
return QueryEnginePort(manifest=build_port_manifest(), config=config)
class TestCancellationBeforeCall:
"""Event set before submit_message is invoked => immediate 'cancelled'."""
def test_pre_set_event_returns_cancelled_immediately(self) -> None:
engine = _fresh_engine()
event = threading.Event()
event.set()
result = engine.submit_message('hello', cancel_event=event)
assert result.stop_reason == 'cancelled'
assert result.prompt == 'hello'
# Output is empty on pre-budget cancel (no synthesis)
assert result.output == ''
def test_pre_set_event_preserves_mutable_messages(self) -> None:
engine = _fresh_engine()
event = threading.Event()
event.set()
engine.submit_message('ghost turn', cancel_event=event)
assert engine.mutable_messages == [], (
'cancelled turn must not appear in mutable_messages'
)
def test_pre_set_event_preserves_transcript_store(self) -> None:
engine = _fresh_engine()
event = threading.Event()
event.set()
engine.submit_message('ghost turn', cancel_event=event)
assert engine.transcript_store.entries == [], (
'cancelled turn must not appear in transcript_store'
)
def test_pre_set_event_preserves_usage_counters(self) -> None:
engine = _fresh_engine()
initial_usage = engine.total_usage
event = threading.Event()
event.set()
engine.submit_message('expensive prompt ' * 100, cancel_event=event)
assert engine.total_usage == initial_usage, (
'cancelled turn must not increment token counters'
)
def test_pre_set_event_preserves_permission_denials(self) -> None:
engine = _fresh_engine()
event = threading.Event()
event.set()
denials = (PermissionDenial(tool_name='BashTool', reason='destructive'),)
engine.submit_message('run bash ls', denied_tools=denials, cancel_event=event)
assert engine.permission_denials == [], (
'cancelled turn must not extend permission_denials'
)
class TestCancellationAfterBudgetCheck:
"""Event set between budget projection and commit => 'cancelled', state intact.
This simulates the realistic racy case: engine starts computing output,
caller hits deadline, sets event. Engine observes at post-budget checkpoint
and returns cleanly.
"""
def test_post_budget_cancel_returns_cancelled(self) -> None:
engine = _fresh_engine()
event = threading.Event()
# Patch: set the event after projection but before mutation. We do this
# by wrapping _format_output (called mid-submit) to set the event.
original_format = engine._format_output
def _set_then_format(*args, **kwargs):
result = original_format(*args, **kwargs)
event.set() # trigger cancel right after output is built
return result
engine._format_output = _set_then_format # type: ignore[method-assign]
result = engine.submit_message('hello', cancel_event=event)
assert result.stop_reason == 'cancelled'
# Output IS built here (we're past the pre-budget checkpoint), so it's
# not empty. The contract is about *state*, not output synthesis.
assert result.output != ''
# Critical: state still unchanged
assert engine.mutable_messages == []
assert engine.transcript_store.entries == []
class TestCancellationAfterCommit:
"""Event set after commit is not observable \u2014 honest cooperative limit."""
def test_post_commit_cancel_is_not_observable(self) -> None:
engine = _fresh_engine()
event = threading.Event()
# Event only set *after* submit_message returns. The first call has
# already committed before the event is set.
result = engine.submit_message('hello', cancel_event=event)
event.set() # too late
assert result.stop_reason == 'completed', (
'cancel set after commit must not retroactively invalidate the turn'
)
assert engine.mutable_messages == ['hello']
def test_next_call_observes_cancel(self) -> None:
"""The cancel_event persists \u2014 the next call on the same engine sees it."""
engine = _fresh_engine()
event = threading.Event()
engine.submit_message('first', cancel_event=event)
assert engine.mutable_messages == ['first']
event.set()
# Next call observes the cancel at entry
result = engine.submit_message('second', cancel_event=event)
assert result.stop_reason == 'cancelled'
# 'second' must NOT have been committed
assert engine.mutable_messages == ['first']
class TestLegacyCallersUnchanged:
"""cancel_event=None (default) => zero behaviour change from pre-#164."""
def test_no_event_submits_normally(self) -> None:
engine = _fresh_engine()
result = engine.submit_message('hello')
assert result.stop_reason == 'completed'
assert engine.mutable_messages == ['hello']
def test_no_event_with_budget_overflow_still_rejects_atomically(self) -> None:
"""#162 atomicity contract survives when cancel_event is absent."""
engine = _fresh_engine(max_budget_tokens=1)
words = ' '.join(['word'] * 100)
result = engine.submit_message(words) # no cancel_event
assert result.stop_reason == 'max_budget_reached'
assert engine.mutable_messages == []
def test_no_event_respects_max_turns(self) -> None:
"""max_turns_reached contract survives when cancel_event is absent."""
engine = _fresh_engine(max_turns=1)
engine.submit_message('first')
result = engine.submit_message('second') # no cancel_event
assert result.stop_reason == 'max_turns_reached'
assert engine.mutable_messages == ['first']
class TestCancellationVsOtherStopReasons:
"""cancel_event has a defined precedence relative to budget/turns."""
def test_cancel_precedes_max_turns_check(self) -> None:
"""If cancel is set when capacity is also full, cancel wins (clearer signal)."""
engine = _fresh_engine(max_turns=0) # immediately full
event = threading.Event()
event.set()
result = engine.submit_message('hello', cancel_event=event)
# cancel_event check is the very first thing in submit_message,
# so it fires before the max_turns check even sees capacity
assert result.stop_reason == 'cancelled'
def test_cancel_does_not_override_commit(self) -> None:
"""Completed turn with late cancel still reports 'completed' \u2014 the
turn already succeeded; we don't lie about it."""
engine = _fresh_engine()
event = threading.Event()
# Event gets set after the mutation is done \u2014 submit_message doesn't
# re-check after commit
result = engine.submit_message('hello', cancel_event=event)
event.set()
assert result.stop_reason == 'completed'