fix: recover TOCTOU + WAL pressure edge case tests

Fix recover path TOCTOU: re-Lookup after AddReplica so the primary
refresh assignment includes the freshly added replica addresses.
Previously, Lookup (copy) was called before AddReplica modified the
registry, so entry.Replicas was empty → primary got replicas=0 →
shipper never configured.

Add 2 WAL pressure edge case tests:
- ShipperCatchUpOrEscalate: 64KB WAL, 200 writes, aggressive flusher.
  Proves no hang/deadlock/corruption. Shipper either keeps up or
  correctly escalates to NeedsRebuild.
- RebuildWithPinWhilePrimaryWrites: rebuild session active while
  primary writes 7600+ blocks in 2s. Proves primary never freezes
  — rebuild pin is on replica only, primary WAL recycles freely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

weed/server/master_block_failover.go

@@ -561,12 +561,16 @@ func (ms *MasterServer) recoverBlockVolumes(reconnectedServer string) {
 			CtrlAddr: ctrlAddr,
 		})
 
+		// Re-lookup entry after AddReplica so the entry copy reflects the
+		// updated replica list. Without this, the stale copy from line 540
+		// has 0 replicas, and the primary refresh assignment gets empty
+		// ReplicaAddrs — the primary never configures its shipper.
+		entry, ok = ms.blockRegistry.Lookup(rb.VolumeName)
+		if !ok {
+			continue
+		}
+
 		// CP13-8: Try catch-up first (Replica assignment), fall back to rebuild.
-		// If the replica can catch up from the primary's retained WAL, this is
-		// much faster than a full rebuild. The shipper's reconnect handshake
-		// (CP13-5) determines whether catch-up or rebuild is actually needed.
-		// If catch-up fails, the shipper marks NeedsRebuild, and the master
-		// sends a Rebuilding assignment on the next heartbeat cycle.
 		if dataAddr != "" {
 			leaseTTLMs := blockvol.LeaseTTLToWire(30 * time.Second)
 			// Send Replica assignment to the reconnected server.

weed/server/master_grpc_server.go

@@ -314,6 +314,13 @@ func (ms *MasterServer) SendHeartbeat(stream master_pb.Seaweed_SendHeartbeatServ
 
 			// Pending assignments (role changes, epoch bumps).
 			pending := ms.blockAssignmentQueue.Peek(dn.Url())
+			if len(pending) > 0 {
+				glog.V(0).Infof("block assign: delivering %d assignment(s) to %s", len(pending), dn.Url())
+				for _, p := range pending {
+					glog.V(0).Infof("  assign: path=%s epoch=%d role=%d replicas=%d",
+						p.Path, p.Epoch, p.Role, len(p.ReplicaAddrs))
+				}
+			}
 
 			// Lease grants for confirmed volumes (lightweight: path+epoch+ttl).
 			// Skip volumes that already have a pending assignment.