fix(review-pr): fail closed on incomplete sub-agent output

[Sayt-0]

Summary

• harden drafter and verifier schemas against empty values, placeholders, and invalid line numbers
• treat failed, refused, malformed, or partial sub-agent responses as incomplete reviews
• aggregate multi-chunk drafter results fail-closed at every finding count
• pair verifier verdicts one-to-one using deterministic finding IDs
• prevent incomplete reviews from carrying the completed-run assessment marker

Context

A structured-output child response terminated with stop_reason: refusal was returned by transfer_task as successful partial JSON.

This change provides action-side containment. It does not change Docker Agent runtime semantics: refusal, structured-output length termination, and native schema validation still require a separate upstream fix.

Observed run: https://github.com/docker/sandboxes/actions/runs/31797481426

Expectation mapping

Expectation	Status	Handling
Refused structured-output child makes transfer_task fail	upstream required	tool errors and malformed partial responses now produce an incomplete review
Partial child transcript remains available	upstream required	no runtime transcript behavior changed
Tool error exposes child and finish reason	upstream required	action fallback reports the affected chunk as incomplete
Completed native output is schema-validated	upstream required	action schemas are hardened against invalid semantic values
Structured max_tokens termination fails equivalently	upstream required	malformed or partial action responses fail closed
line >= 1 and meaningful strings	implemented	both drafter and verifier schemas enforce the constraints
Verdicts correspond one-to-one with findings	implemented	deterministic finding_id pairing plus exact file and line cross-check
One failed chunk prevents an approving review	implemented	incomplete state overrides all confidence-based assessment labels

Validation

Check	Result
Unit tests	pass, 857 tests
Typecheck	pass
Biome	pass
Build	pass
Actionlint	pass
YAML parsing	pass
Docker Agent config dry-run	pass
Integration assertions	15/15 pass; local Vitest teardown timeout also reproduces on origin/main
Live model evaluation	skipped, requires provider credentials