fix(workflow): retire status:pr-open on every terminal PR transition (Closes #780)

status:pr-open was applied by gitea_create_pr and never removed again. Every
terminal path finished without touching it, so a repository audit found 40
closed issues still advertising an open PR.

Add terminal_pr_label_cleanup.py as the single authoritative rule and route
every sanctioned terminal path through it, so the paths cannot drift:

- merge (gitea_merge_pr)
- close without merge (gitea_edit_pr)
- supersession/abandonment (gitea_reconcile_superseded_by_merged_pr)
- already-landed reconciliation (gitea_reconcile_already_landed_pr)
- controller closure (gitea_close_issue)
- retry/recovery (new gitea_cleanup_terminal_pr_labels)

The rule removes only status:pr-open, preserves every other label, allows an
empty resulting set, is a no-op when the label is absent (so retries are
safe), and confirms the outcome by read-after-write rather than assumption.

Controller closure runs the cleanup before the state change and fails closed
if it cannot be completed and verified; closing first would bake in the stale
label with no later step to catch it. Post-merge cleanup never blocks the
merge, which already happened, and reports failures with a safe next action.

Also:
- gitea_assess_terminal_label_hygiene: read-only terminal validation that
  reports residual status:pr-open, exempting issues with a genuinely open PR.
- _put_issue_label_names now accepts Gitea's empty response body when the
  requested set is empty, so clearing the last label works.
- test_audit's close_issue fixture keys on the request instead of call order,
  since closing now also reads labels for the cleanup and its read-back.

Docs: label-taxonomy terminal-transition section, runbook pointer, and the
review-merge / reconcile-landed final-report terminal-label requirements.

Suite: 4045 passed, 11 failed, 6 skipped. The same 11 failures reproduce on
clean master df31674 (4010 passed, 11 failed) and are pre-existing.

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

skills/llm-project-workflow/schemas/reconcile-landed-final-report.md

@@ -39,6 +39,7 @@ occurred).
 - Git ref mutations:
 - MCP/Gitea mutations:
 - Reconciliation mutations:
+- Terminal label cleanup:
 - External-state mutations:
 - Read-only diagnostics:
 - Blockers:
@@ -52,6 +53,13 @@ Identity format: `username / profile` (not personal email unless required — #3
 
 `git fetch` belongs under `Git ref mutations`, not read-only diagnostics (#297).
 
+`Terminal label cleanup` (#780) reports the `pr_open_label_cleanup` record the
+reconciliation tool returned — `clean` / `failed` / `not applicable (no linked
+issue)`, with the labels removed and preserved. Reconciliation is a terminal
+transition, so a non-`clean` record blocks any "reconciled" claim; recover with
+`gitea_cleanup_terminal_pr_labels` (`terminal_reason='retry_recovery'`) and
+confirm with `gitea_assess_terminal_label_hygiene`.
+
 The report must also carry the canonical self-propagating handoff block
 (`schemas/self-propagating-handoff.md`, #626) and that block must be posted to
 the Gitea issue or PR thread.

skills/llm-project-workflow/schemas/review-merge-final-report.md

@@ -99,6 +99,21 @@ Narrative final report and controller handoff must agree on eligibility class,
 candidate/reviewed head SHA, mutation state, worktree usage, review decision,
 terminal review mutation, merge result, and linked issue status.
 
+### Terminal label state (#780)
+
+A run that takes a PR to a terminal state — merged, closed without merge,
+superseded, or reconciled as already landed — must report what happened to the
+linked issue's `status:pr-open` label, quoting the `pr_open_label_cleanup`
+record the terminal tool returned:
+
+- Terminal label cleanup: `clean` / `failed` / `not applicable (no linked issue)`
+- Labels removed and preserved per issue, with the read-after-write read-back
+
+Never claim the transition is complete while that record is not `clean`. A
+failed cleanup does not undo the merge; the safe next action is
+`gitea_cleanup_terminal_pr_labels` with `terminal_reason='retry_recovery'`,
+confirmed by `gitea_assess_terminal_label_hygiene`.
+
 ### Proof-backed claims (#395)
 
 Proof-sensitive claims must cite explicit command/tool evidence in the report