refactor(loop): convert _process_message to functional state machine#3715
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- Extract TurnState enum and TurnContext dataclass - Extract state handlers: _state_restore, _state_compact, _state_command, _state_build, _state_run, _state_save, _state_respond - Extract _process_system_message for system message short-circuit - Driver loop uses getattr dispatch over explicit state transitions - Preserve all existing behavior (794 tests passing)
- Fix _assemble_outbound on_stream type annotation (Callable[[str], Awaitable[None]] | None) - Use last_msg consistently in _state_save instead of re-indexing - Remove dead fallback in _state_respond (guaranteed non-None by _state_save) - Change pending_summary type from Any to str | None - Make session optional in TurnContext to avoid redundant fetch - Add defensive dispatch with RuntimeError for missing handlers
- State handlers now return event strings ('ok', 'dispatch', 'shortcut')
- Driver loop uses _TRANSITIONS lookup table: (state, event) -> next_state
- State graph is centralized and visible at a glance
- Added StateTraceEntry to record per-state timing and events
- Driver loop logs state duration + event at debug level
- Exception paths are traced with error field for observability
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- TurnContext now carries a turn_id (session_key:time_ns) - All state transition debug logs include [turn_id] prefix - RuntimeError messages also include turn_id for observability
This was referenced May 10, 2026
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Summary
Refactor the 300-line
_process_messagemethod into an explicit functional state machine to improve readability and maintainability.Changes
RESTORE → COMPACT → COMMAND → BUILD → RUN → SAVE → RESPONDTurnStateenum andTurnContextdataclass to carry cross-state data_process_system_messagemethodgetattrdispatch (while ctx.state != DONE)Verification
pytest tests/agent/— 794 passedruff check nanobot/agent/loop.py— clean