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loopctl

`src/engine/core/machine.rs` — the `LoopMachine`

The brain: pure, serializable state; decides every step; never does IO. (~1,600 lines with docs/tests.)

Key items

  • Fields: state, history, pending, pending_tools, turns_taken, context_tokens, cancelled, last_compaction_tokens.
  • Steps & feeds: next_step(policy); model_response (classifies tool calls against available_tools, pre-answering unknown ones), tool_results (the only pending_tools consumer), compaction_result (wholesale replace + pending clear), compaction_noop (buffers untouched), set_context_tokens, inject, cancel, fail, accept_input.
  • Maintenance: commit_pending, discard_pending.
  • Reads: history, full_history, state, turns_taken, is_terminal, is_cancelled.
  • MachinePolicy { max_turns, context_window, compact_threshold, auto_compact } — passed fresh each step, never stored.
  • Serialize + Deserialize — checkpoint/resume round-trips pinned by tests (identical decisions after restore).

Behavior notes

  • Decision order per step: terminal → cancelled → (model-side) turn limit → emergency ≥95% → threshold >N% → CallLLM.
  • next_step is pure and repeatable; terminal is forever; fail() guarantees an errored machine carries its failure into serialization.
  • The no-progress guard (tokens_after >= tokens_before → Failed(ContextExceeded)) runs in both compaction feeds, before any buffer mutation.

Deep dive: The state machine.