Two fixes:
1. TestReconnect_GapBeyondRetainedWal_NeedsRebuild: rewritten to test the
real reconnect handshake gap detection path (R < S in
reconnectWithHandshake). Sequence: establish sync → disconnect →
release retention hold via timeout → write + flush to advance WAL past
replica position → reconnect → handshake detects R=0 < S=9 → NeedsRebuild.
Log proves: "reconnect: gap too large R=0 H=8 S=9"
2. TestReplicaState_RebuildComplete_ReentersInSync: reclassified from
primary proof to support evidence (does not start from live NeedsRebuild
shipper state, but proves rebuild mechanics work end-to-end).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
