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_on_turn fires after every agent turn and called _persist() inline — a synchronous open()+json.dump() over the full history/display_history/ workflow_turns. As a session grows this write grows with it, and being awaited directly in run_agent_loop it stalls the event loop on every single turn (TUI freezes, no other coroutine gets to run). Move it to asyncio.to_thread, awaited so writes stay ordered turn to turn and the resume checkpoint can't be overwritten out of order. Benchmarked with a 2000-message history + a concurrent heartbeat coroutine: sync persist blocks the loop for ~139ms with 0 heartbeat ticks; to_thread lets ~4558 ticks through with a 0.85ms max stall.
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Copilot review overview
🟡 Changes recommended
Persistence must remain serialized and safe during cancellation.
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Review effort: Lite
Findings: 1
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What changed in this PR
Moves per-turn session persistence off the asyncio event loop to keep the TUI and streaming responsive.
Changes:
- Runs
_persist()viaasyncio.to_thread. - Keeps persistence awaited between turns.
| File | Summary |
|---|---|
apodex/session.py |
Offloads checkpoint writes; cancellation can allow concurrent persistence and risk checkpoint corruption. |
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| # _persist() does synchronous file I/O over the full history; run it | ||
| # off the event loop so long sessions don't stall on every turn. | ||
| # Awaited (not fire-and-forget) so writes stay ordered turn-to-turn. | ||
| await asyncio.to_thread(self._persist) |
_persist() now runs on both the main thread (start_new_session, rename_session) and a to_thread worker (_on_turn), so overlapping writers could interleave and corrupt session.json. Serialize writes with a threading.Lock and write via tmp file + os.replace so a torn write is never observable on disk.
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Summary
TerminalSession._on_turnfires after every agent turn (run_agent_loopawaitson_turn_completedirectly) and called_persist()inline — a synchronousopen()+json.dump()over the fullhistory,display_history, andworkflow_turns.asyncio.to_thread, still awaited so writes stay ordered turn-to-turn (no risk of an out-of-order write corrupting the--resumecheckpoint).Benchmark
2000-message history, 10 persists, with a concurrent heartbeat coroutine standing in for other async work:
Sync blocks the loop completely (0 heartbeat ticks in 139ms).
to_threadcosts a bit more wall time (thread dispatch + GIL handoff) but lets everything else keep running concurrently — the actual user-visible win, since the write itself isn't the bottleneck, the freeze is.Test plan
uv run pytest apodex/tests/test_changes.py apodex/tests/test_features.py— 136 passeduv run ruff check apodex/session.py— clean