The original implementation lane merged cleanly, but its tasks.md cleanup section still showed the finish steps as incomplete. This backfills the PR URL, merge timestamp, and worktree-prune proof so the merged OpenSpec record matches what actually happened.

Constraint: The evidence patch had to land after PR #375 merged because the exact mergedAt timestamp and cleanup result were only known at finish time.
Rejected: Leave the stale cleanup boxes on main | cleanup evidence is part of the repo workflow contract and would misstate merged truth.
Confidence: high
Scope-risk: narrow
Directive: When a finish flow merges a change before tasks.md records PR and MERGED proof, follow with a tiny bookkeeping lane instead of leaving stale cleanup boxes behind.
Tested: git status --short; git diff --stat; gh pr view agent/codex/reduce-prompt-replay-checkpoint-guidance-2026-04-23-15-43 --json url,state,number,headRefName,baseRefName,mergedAt; git worktree list
Not-tested: automated test suite (docs-only bookkeeping patch)