[Michael Avrukin (mavrukin)]

Adds local_model=fm, off by default: the loop guard's judge runs on Apple's Foundation Models CLI (/usr/bin/fm, macOS 27 with Apple Intelligence) instead of claude -p / codex exec / …. It costs 0 tokens, and it still answers while the agent's CLI is signed out. On other systems the setting does nothing.

Rationale, method and every result, including what did not work: #186.

Results

Judge, replayed on 302 real loop-guard decision points. I took 502 public SWE-agent trajectories (nebius/SWE-agent-trajectories) and replayed them through this repo's TurnGuard, default thresholds. Each verdict below comes from llm_stuck_judge, through TE's stock claude_call for Haiku and this PR's fm_call for fm. A redirect is stuck with confidence at or above the threshold.

Judge	threshold	redirected, resolved runs ↓	redirected, context-exhausted runs	redirected, other unresolved	AUC	tokens / call	s / call
Haiku 5.5 (current default)	0.70	26/52 (50%)	115/150 (77%)	53/100 (53%)	0.684	6,981	3.9
Haiku 5.5	0.85	10/52 (19%)	63/150 (42%)	21/100 (21%)	0.684	6,981	3.9
fm, this PR (local_judge_confidence 0.9)	0.90	7/52 (13%)	56/150 (37%)	13/100 (13%)	0.639	0	2.0
fm without the floor	0.70	37/52 (71%)	123/150 (82%)	76/100 (76%)	0.639	0	2.0
fm without a schema (free text)	0.70	4/52 (8%)	13/150 (9%)	2/100 (2%)	0.383	0	1.9

• fm's confidences come in coarse steps (0.65/0.72/0.85/0.92). At the guard's 0.7 it lets nearly every "stuck" verdict through, hence local_judge_confidence=0.9.
• At that floor fm sits close to Haiku's own trade-off curve, slightly below it (AUC 0.64 vs 0.68). It redirects fewer resolved runs than Haiku at 0.85, and catches fewer loops.
• The 302 Haiku calls cost 2.1M effective tokens; the same calls on fm cost 0.
• Without a schema fm can't tell loops from successes: it redirects 9% of exhausted runs' points and 8% of resolved runs' (AUC 0.38). In 182 of its 283 "not stuck" verdicts, the reason contains a loop phrase such as "repeated identical failures". So the judge always passes its verdict schema (fm respond --schema).

Changes

• plugin/sidecall.py:
  • local_routes: the settings and the platform only, no subprocess.
  • fm_available: runs /usr/bin/fm by its full path, on macOS only.
  • fm_call: prompt on stdin, greedy decoding, optional JSON schema.
  • local_runner, and a role argument to runner_for.
  • Without fm, the call goes to the agent's CLI. A call fm can't answer is logged and goes there too.
• plugin/judge.py: the judge and the redirect writer each get their own runner. A local stuck verdict below local_judge_confidence spares the turn. A local call is charged 0 tokens.
• plugin/controller.py: while the host is paused, PostToolUse picks the judge from the settings alone, so no hook runs fm. The judge's own job checks that the model answers. plugin/fold.py: role-aware runner.
• plugin/config.py: local_model, local_roles (default judge) and local_judge_confidence (0.9), with TE_* variables.
• Docs: plugin/README.md (On-device side calls) and one sentence in README.md. The plugin's own text makes no claims of effect.
• Tests: tests/test_local_model.py (29 tests). fm and the platform are faked, so they run on Linux CI. conftest.py fakes fm like the other side calls.
  • python -m pytest tests experiments/tests: 1,315 passed, 22 skipped on 3.13. tests also passes on 3.10.
  • scripts/dead_code.py reports nothing new compared with main.

After review

main was merged in, with no force push. The conflicts were additions next to #187's per-agent model settings; both are kept. Then two commits:

• plugin: drop media=audio. It's out of scope here; we'll consider it as a separate plugin.
• plugin: local judge review fixes:
  • no fm check in a hook;
  • /usr/bin/fm on macOS only;
  • the docstring points at Apple's on-device model (fm) for TokenEconomizer's side calls and audio prompts: approach, rationale and results #186;
  • a docs fix.

Not covered

• Only verified on macOS 27.0.1 on an M2 with Claude Code.
• The judge comparison uses SWE-agent (Llama) trajectories mapped onto TE's tool names, and a shared envelope rather than a per-repo one. It is not a rerun of the paper's arms; that needs the Linux/Docker harness.
• In my live Claude Code runs, the fm judge answered, and a paused host still got verdicts. I couldn't produce an organic loop that ended in an fm redirect reaching the model, because Haiku 5.5 stops on its own when tests contradict each other.

🤖 Generated with Claude Code

https://claude.ai/code/session_01UporVpn64UvJqEnurKVwza

[Aaron Li (aaron-jx-li)]

Thanks for the careful write-up in #186. We'd like to take the two options separately.

On-device judge (local_model=fm): we can take it with small changes.

1. controller.py probes fm available inside the PostToolUse hook while the host is signed out. That runs on every tool call, because each hook is a new process. Please check only the config there.
2. Please call /usr/bin/fm by its full path and only on macOS, instead of looking it up on PATH.
3. Please point the config.py docstring at #186 instead of quoting the comparison with Haiku.

Audio transcripts (media=audio): we're not taking this one. The plugin reads finished sessions to change what later sessions cost, and transcribing files at prompt time is outside that. It would also be our first compiled helper, which CI can't build or test. If you'd like to keep it, it could live as a separate plugin. For reference, two bugs we found:

• With repomap=on, outputs = self._inject_map(...) replaces the transcript on the first prompt.
• Transcription can take up to 45 s inside a prompt hook whose limit is 20 s, and a killed hook also loses the loop guard's new turn.

Could you split the first commit into its own PR, rebased on main?

[Michael Avrukin (mavrukin)]

Thanks for the review. This PR is now just local_model=fm. I merged main into the branch rather than rebasing, so there was no force push, and added two commits:

• plugin: drop media=audio. Audio is out. We'll consider it as a separate plugin, outside TokenEconomizer. You're right about both bugs:
  • With repomap=on, _inject_map replaced the transcript.
  • Up to 3 files × 15 s of transcription could overrun the prompt hook's 20 s limit, and lose the loop guard's new turn with it.
• plugin: local judge review fixes:
  1. While the host is paused, controller._judge now reads only the config: sidecall.local_routes checks local_model, local_roles and the platform, with no subprocess. The fm available check runs only in the judge's detached job, and if the model doesn't answer, the turn is spared. A new test runs _judge for a paused host with fm and subprocess.run set to fail if called. It fails on the old code.
  2. /usr/bin/fm by its full path, only on macOS. It's never looked up on PATH.
  3. The config.py docstring points at Apple's on-device model (fm) for TokenEconomizer's side calls and audio prompts: approach, rationale and results #186 instead of quoting the Haiku comparison.

The merge with main only conflicted where #187's per-agent paid_model/effort settings sit next to the new ones; both are kept. tests and experiments/tests pass on 3.13, tests passes on 3.10, and scripts/dead_code.py reports nothing new compared with main. I've updated the PR description to match.

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