feat: add reconciler supersession close gate

docs/llm-workflow-runbooks.md

@@ -811,6 +811,32 @@ author work. Do not switch from `prgs-reconciler` to `prgs-author` only to run
 - **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.`
 
+### Superseded PR / satisfied issue reconciliation (#525)
+
+Closing duplicate or superseded PRs after a canonical PR has merged is
+**reconciler** work. Do not switch to `prgs-author` only to close the duplicate
+PR, close the satisfied issue, or file a narrow follow-up discovered during
+reconciliation.
+
+- **Profile:** `prgs-reconciler`.
+- **Tasks:** `reconcile_close_superseded_pr`,
+  `reconcile_close_satisfied_issue`, and
+  `reconcile_create_followup_issue`.
+- **Tool:** `gitea_reconcile_superseded_by_merged_pr`.
+- **Required proof:**
+  1. Live target PR state is open, but it is not independently required and no
+     mergeable work remains.
+  2. Live superseding PR state is closed and merged.
+  3. Superseding PR head is an ancestor of freshly fetched `master`.
+  4. Merge commit SHA is recorded.
+  5. Canonical close comment cites the superseding PR and merge commit.
+  6. Linked issue closure is attempted only when the issue is open and
+     explicitly satisfied by the superseding PR.
+- **Fail closed:** missing ancestry proof, missing canonical comment,
+  mergeable target PR, same target/superseding PR, or missing
+  `gitea.pr.close` / `gitea.issue.close` capability.
+- **Prompt:** `As prgs-reconciler, reconcile PR #N as superseded by merged PR #M; post the canonical close comment, close the superseded PR, and close issue #K only if the merged PR fully satisfies it.`
+
 ### Stop on blocker
 
 - **Any profile.** If a required gate cannot be satisfied — identity