Make invariant-suite baseline provenance immutable across agent handoffs #213

Summary

The invariant-suite retry/handoff implementation stores invariant-suite-baseline.json under the task artifact directory, which is passed to the model agent as a writable addDir. After the agent returns, prepareArtifactMirror sees the existing sidecar and skips recapturing it; changedTestTreePaths then trusts the agent-controlled hashes. A model can therefore edit the sidecar to make generated or modified invariant files appear unchanged, preventing them from reaching the durable invariant-suite handoff.

Expected behavior

The baseline used for change detection must be immutable to the agent: derive changes from the pinned source ref, retain a process-owned digest, or store/verify a durable baseline outside agent-writable artifact roots. Retries and resumed runs must preserve the original baseline without recapturing after failed-attempt edits.

Reproduction shape

1. Start an invariant stage and let preparation create invariant-suite-baseline.json.
2. Modify a tests/... or test/... harness source and edit the baseline entry's SHA-256/size in the agent-visible artifact directory.
3. Return from the agent.
4. The post-agent materializer compares against the edited sidecar and omits the changed source from invariant-suite/.

The resulting downstream campaign can run without the generated CryticTester/Properties/TargetFunctions sources despite a successful implementation task.