Tolerate omitted empty structured review collections

[wwind123]

Summary:

• default omitted structured PR review follow-up arrays to empty lists instead of rejecting the payload
• apply the same normalization to structured plan reviews for the analogous optional-empty collections
• add regression coverage for both parser paths

Tests:

• python3 -m pytest

Fixes #170

[wwind123]

Implemented the fix in PR #172.

Structured PR reviews now treat omitted optional-empty collections as [] instead of rejecting the payload, while still requiring fields with actual semantic content such as prior_item_dispositions. I applied the same normalization to the analogous structured plan-review fields and added regression tests for both parser paths.

Tests: python3 -m pytest (passed)

-- OpenAI Codex

[wwind123]

{
  "schema_version": 1,
  "kind": "pr_review",
  "state": "approved",
  "summary": "Clean, minimal fix. Moves the three semantically optional array fields to `optional` in `_expect_exact_keys` and introduces `_expect_optional_string_list` that defaults a missing field to `[]` before delegating to the existing validated `_expect_string_list`. The same treatment is applied symmetrically to the plan-review parser. Regression tests for both paths confirm the behaviour. No correctness, security, or maintainability concerns.",
  "blocking_items": [],
  "same_pr_followups": [],
  "future_followups": [],
  "prior_item_dispositions": []
}

-- Anthropic Claude

[wwind123]

{
  "schema_version": 1,
  "kind": "pr_review",
  "state": "approved",
  "summary": "The PR correctly implements tolerance for omitted empty collection fields in structured PR and plan reviews. By introducing the `_expect_optional_string_list` helper and updating the schema validation to support `optional` fields, the orchestrator now gracefully handles payloads that omit fields like `blocking_items` or `future_followups` when they are empty. The changes are logically sound, follow the requested direction, and include comprehensive test coverage for both PR and plan review paths.",
  "prior_item_dispositions": []
}

-- Google Gemini