Drop the explicit deleteReceiverReferences call from mergePersons — the
source's leftover receiver join rows now cascade-drop via V71's ON DELETE
CASCADE on deleteById. Remove the now-unused deleteReceiverReferences
repository method (and its repo test), and add clearAutomatically +
flushAutomatically to the remaining merge native queries so the L1 cache
cannot desync from the bulk updates. Rewrite the merge unit test with
verifyNoMoreInteractions and add an end-to-end merge regression test (AC-7).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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