Harden markdown response parsing against formatting drift

[wwind123]

Summary

• accept parenthesized empty placeholders like (none) and (n/a) in follow-up and prior-disposition sections
• preserve raw prior-disposition prose for validation, add precise malformed-bullet errors with section and line context, and keep contradictory active placeholders invalid
• add a narrow prose-only fallback for explicit blanket resolution language and cover the new parser/validator behavior with regressions

Testing

• python3 -m pytest tests/test_agent_loop.py -k "plan_review or approved_followups or unresolved_item_dispositions"
• python3 -m pytest

Fixes #144

[wwind123]

Implemented the hardening for issue #144 in PR #166.

The parser now accepts parenthesized empty placeholders like (none) and (n/a) in follow-up and prior-disposition sections, preserves raw prior-disposition prose for validation, and reports malformed prior-disposition bullets with the exact section heading and source line. The validators now also accept a narrow prose-only blanket-resolution fallback for exact phrases like all carried-forward items are resolved, while still rejecting mixed bullet-plus-prose coverage and ambiguous wording.

Tests:

• python3 -m pytest tests/test_agent_loop.py -k "plan_review or approved_followups or unresolved_item_dispositions" ✅
• python3 -m pytest ✅

-- OpenAI Codex

[wwind123]

{
  "schema_version": 1,
  "kind": "pr_review",
  "state": "approved",
  "summary": "The implementation correctly addresses all three hardening goals from issue #144: parenthesized empty-placeholder support, a narrow blanket-prose fallback for prior-dispositions sections, and precise section/line error messages. All 380 tests pass including the new targeted regressions. The mechanics are deterministic and well-scoped.",
  "blocking_items": [],
  "same_pr_followups": [],
  "future_followups": [],
  "prior_item_dispositions": []
}

-- Anthropic Claude

[wwind123]

=== AGENT_LOOP_PUBLIC_RESPONSE_BELOW ===
{
"schema_version": 1,
"kind": "pr_review",
"state": "approved",
"summary": "The PR successfully hardens the markdown response parser as planned. It adds support for parenthesized placeholders like (none) and (n/a), improves error diagnostics with section and line metadata, and implements a narrow prose fallback for blanket resolutions of carry-forward items. Comprehensive regression tests confirm the new behavior and ensure no regressions in existing parsing logic.",
"blocking_items": [],
"same_pr_followups": [],
"future_followups": [],
"prior_item_dispositions": []
}

-- Google Gemini