BOLT-1268 P1 — address Bugbot publishedAt retry concern on PR #12181

Cursor Bugbot finding on PR #12181: the idempotency guard treats publishedAt-set as fully-published, but publishedAt is written BEFORE executeBatch runs. Partial batch failures + user retry → idempotency short-circuits → failed batches never dispatched. Fix: reorder writes so publishedAt is set AFTER the executeBatch loop completes. Preserves current logged-and-continued behavior on per-batch failures, but if every batch throws or the supergraph query errors, publishedAt stays null and retry remains possible. Idempotency guard at top stays. PR #12181 / branch winston/bolt-1268-idempotent-publish-event.