Harden Piranha utility mutation campaigns - #1
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D1: ModelEngine (portfolio/model_engine.py) — a model-driven Engine that
delegates candidate generation to a pluggable proposer (in-process deterministic
for the verifier; real LLM CLI via ClaudeCodeEngine for production). Sits below
the sandbox/safety guards; writes only under ctx.workdir; never raises.
D2: make_engine('model', ...) + --engine choices {model,codex,claude-code} in
tools/piranha.py. No safety override added; non-shell engines require an explicit
--engine-command (no fake default).
D3: tools/piranha_model_verify.py — a deterministic, offline end-to-end verifier
(no sys.executable, no network) proving the planted improvement wins the champion,
a null variant is demoted (never champion) under the improvement gate, and S1-S4 +
blast-radius parity + source immutability + report-always-written all hold. Emits
'PIRANHA-MODEL-ENGINE-VERIFY: PASS'. Non-vacuous (sensitivity-probed: an escaping
write, a raising proposer, and a false-champion are all caught).
Also fixed the historical env-flaky shell-engine tests toward determinism by
quoting the (space-containing) interpreter path — no assertion weakened. Piranha
suite now 20/20 (+ verifier) green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Summary
Safety and behavior
The original source tree remains byte-identical. Candidate code is tested only in an owned sandbox and fails closed when required confinement evidence is unavailable. Promotion evidence comes from trusted metrics rather than candidate-supplied values.
Known limitation: macOS resident-memory enforcement is supervisory; hostile native code still belongs in a memory-capped VM or container.
Verification
PIRANHA-UTILITY-VERIFY: PASSPIRANHA-MODEL-ENGINE-VERIFY: PASS