fix: strengthen reconciler merged cleanup tests and runbook (#523)

Make the preflight bypass test actually exercise purity (not test short-circuit),
cover unmerged/open-head fail-closed cleanup, and document post-merge cleanup
ownership for prgs-reconciler so authors are not required for that path.

docs/llm-workflow-runbooks.md

@@ -738,6 +738,27 @@ merger handoff.
 - **Prompt (normal):** `After verifying master contains the merge of PR #N using post-merge file-presence verification, close issue #M and delete the merged branch. Include verification details in the report.`
 - **Prompt (reconcile):** `Reconcile closed-not-merged PR #N by verifying if its content landed on master.`
 
+### Post-merge merged cleanup ownership (#523)
+
+Post-merge **local worktree / remote branch cleanup** is **reconciler** work, not
+author work. Do not switch from `prgs-reconciler` to `prgs-author` only to run
+`gitea_reconcile_merged_cleanups`.
+
+- **Profile:** `prgs-reconciler` (task `reconcile_merged_cleanups` /
+  `reconciliation_cleanup`).
+- **Namespace:** reconciler MCP server; stable control checkout is allowed for
+  this role (branches-only author guard does not apply).
+- **Steps:**
+  1. `gitea_whoami` + `gitea_resolve_task_capability(task="reconcile_merged_cleanups")`.
+  2. Dry-run first: `gitea_reconcile_merged_cleanups(dry_run=True)`.
+  3. Execute only after audit/authorization gates when remote branch delete or
+     worktree removal is required (`dry_run=False`, `execute_confirmed=True`,
+     and `gitea.branch.delete` when deleting remotes).
+- **Fail closed:** unmerged/open heads, mismatched worktrees, and non-merged
+  closed PRs must not be cleaned.
+- **Reports:** label cleanup actions as reconciler cleanup (not author mutation).
+- **Prompt:** `As prgs-reconciler, dry-run then execute gitea_reconcile_merged_cleanups for recently merged PRs without switching to prgs-author.`
+
 ### Stop on blocker
 
 - **Any profile.** If a required gate cannot be satisfied — identity