Stabilize mixed-history resume reconstruction

[wwind123]

Fixes #157

Summary

• stabilize mixed-history resume reconstruction around AGENT_LOOP_META so the active round ledger follows the latest metadata-backed subject/head state
• fail closed with AgentLoopError when resumed reviewer dispositions do not match the reconstructed prior-item ledger
• add mixed-history resume regressions and document the structured-response contract and legacy fallback surface

Testing

• python3 -m pytest tests/test_agent_loop.py -k "resume_pr_round or resume_plan_round or hybrid_history or missing_reconstructed_prior_item"
• python3 -m pytest

[wwind123]

Implemented the #157 plan.

PR: #171

Tests: python3 -m pytest tests/test_agent_loop.py -k "resume_pr_round or resume_plan_round or hybrid_history or missing_reconstructed_prior_item" passed; python3 -m pytest passed.

-- OpenAI Codex

[wwind123]

{
  "schema_version": 1,
  "kind": "pr_review",
  "state": "approved",
  "summary": "Solid stabilization of mixed-history resume reconstruction. `_select_current_round_records` correctly anchors to the most-recent record for a subject and uses prior-items signature matching to exclude stale replay ledgers. `_record_prior_item_disposition` replaces the bare dict append with a fail-closed `AgentLoopError`, directly fixing the `KeyError: item-1` crash from the issue thread. Four new regression tests cover all three failure modes called out in the issue comment (plan-first replay with wrong active item set, hybrid history preferring metadata over legacy markdown, and the KeyError-on-unknown-item crash). Documentation in README and local_agent_loop.md clearly states the three-level fallback order and the intentionally narrow remaining legacy surface. All 414 tests pass.",
  "blocking_items": [],
  "same_pr_followups": [],
  "future_followups": [],
  "prior_item_dispositions": []
}

-- Anthropic Claude

[wwind123]

Stabilizes mixed-history resume reconstruction by isolating current round records using a prior-item ledger signature and replaces KeyError crashes with descriptive AgentLoopErrors.

-- Google Gemini