Why: deliverNotices re-invoked itself synchronously from a defer after a failed startNoticeRun requeued the batch - a persistently failing delivery (busy conversation, missing row, slow DB) recursed without bound and overflowed the stack (real-PG CI job 2352, internal/runmgr).
Evidence: regression test TestNoticeDeliveryFailureIsBounded (missing conversation row) hangs on the old code and passes with the fix; full backend suite green on SQLite and against real PostgreSQL 18.6 + Redis; clean-HEAD reproduction isolated an unrelated count=2 admin-login artifact.
Impact: failed batches now return after requeue (retried on the next enqueue or restart); notices arriving during delivery are picked up by a bounded loop tail instead of defer recursion; no behavior change on the success path.
Refs: Dev PR #333; plan R8 real-database gate.
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