feat: require transient validation failure history in reviewer reports (Closes #396)

Add assess_validation_failure_history_report so reviewer final reports must
document every validation failure observed during a session, not only the
final passing result. Wire the verifier into final_report_validator,
gitea_validate_review_final_report, and the review-merge workflow template.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

skills/llm-project-workflow/workflows/review-merge-pr.md

@@ -538,6 +538,36 @@ Official validation integrity status must be one of:
 
 Do not invent a softer status.
 
+## 21A. Validation failure history rule
+
+Every validation failure observed during the review session must appear in the
+final report, even if a later rerun passes.
+
+Before claiming `Validation: passed`, list every failed validation command from
+the session under `Validation failure history`.
+
+For each failure, report:
+
+* command
+* failing test or error
+* suspected cause
+* whether it reproduced
+* whether it exists on baseline master
+* evidence for whether it is or is not PR-caused
+
+If a later rerun passes, also report:
+
+* what changed between runs
+* whether environmental state was cleaned (for example `/tmp` lock files)
+* why the pass is trustworthy
+
+If the cause is unknown, do not erase the earlier failure with plain
+`Validation: passed`. Use a status such as
+`passed after transient failure investigation`.
+
+`gitea_validate_review_final_report` rejects reports that omit known earlier
+validation failures when `validation_session.observed_failures` is supplied.
+
 ## 22. Baseline validation rule
 
 Do not run tests in the main checkout.
@@ -1096,6 +1126,7 @@ Controller Handoff:
 * Baseline worktree path:
 * Files reviewed:
 * Validation:
+* Validation failure history:
 * Official validation integrity status:
 * Terminal review mutation:
 * Review decision: