flow: replication + handoff across instances + 6 tests (Phase 4 complete)

flow-replicate-to copies the plain-data store export to a peer's replica slot;
flow-restore-from imports it. Handoff = replicate, local instance dies, peer
restores and resumes by id. The replay log survives the move, so all resolved
suspends carry over. Same durable-data mechanism as crash recovery, across
instances. All four phases complete: 93/93.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/flow/conformance.sh

@@ -52,7 +52,7 @@ emit_eval () { echo "(epoch $EPOCH)"; echo "(eval \"$1\")"; EPOCH=$((EPOCH+1));
   done
 } > "$TMPFILE"
 
-OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>&1 || true)
+OUTPUT=$(timeout 300 "$SX_SERVER" < "$TMPFILE" 2>&1 || true)
 
 TOTAL_PASS=0
 TOTAL_FAIL=0