[Route Weight][testgen] Add round-1 repo-review schema validator edge tests

[stranske]

Why

scripts/repo_review_round1_schema.py gates round-1 reviewer findings before they feed the weekly repo-review workflow. The validator contains subtle checks for repo-relative refs, generic summaries, Workflows misroutes, candidate substance, and expected repo matching. This is a safe Route-Weight testgen opener because it is pure JSON validation.

Scope

• Add focused tests for scripts/repo_review_round1_schema.py.
• Cover _looks_like_repo_relative_path() with bare paths, :line ranges, markdown anchors with spaces, URLs, prose with spaces, and empty values.
• Cover validate_implementation_piece() required fields and allowed statuses.
• Cover validate_candidate() for generic gap phrases, invalid refs, too-short fields, missing test-like AC, Workflows misroute title tokens, and valid candidate acceptance.
• Cover validate_findings() for expected repo mismatch, pilot agent allowance, generic summaries, and a fully valid minimal payload.

Acceptance Criteria

• Tests use in-memory payload dictionaries only.
• Tests assert precise error substrings for the important guardrails.
• Existing schema contract remains strict.

Validation

pytest -q tests/scripts/test_repo_review_round1_schema.py

Route-Weight Metadata

• task_type: testgen
• lane: opener
• safe_opener: true
• defect_class: repo-review-round1-schema-coverage-gap
• source: 2026-06-27-direct-exploration-next-wave

Non-Goals

• Do not relax the schema to make tests pass.
• Do not change repo-review prompts.
• Do not write report artifacts.

[stranske]

Closer sequencing note: PR #2627 was merged and labeled verify:compare. Reopening this source issue until durable verifier/provider comparison PASS is available, or until any non-PASS verifier result is dispositioned with evidence/follow-up.

[stranske]

verify:compare Outcome

• PR test: cover dependency test setup validator #2627 merged and carries verify:compare.
• Verifier run 28325585430 completed successfully.
• Provider comparison report: test: cover dependency test setup validator #2627 (comment)
• Verdict: PASS from both providers. Current PR checks are green.

Disposition: issue #2620 is complete.