refactor: Task A — canonical identity/recovery rules via bridge helpers

Remove direct fmt.Sprintf identity construction from v2bridge/control.go.
Both convertReplicaAssignment and convertRebuildAssignment now use:
- bridge.ReplicaAssignmentForServer (canonical ReplicaID derivation)
- bridge.RecoveryTargetForRole (canonical role → SessionKind mapping)

Before: 3 call sites with inline fmt.Sprintf("%s/%s", vol, server)
After: 0 — all identity construction goes through sw-block canonical helpers

volume_server_block.go already used bridge helpers (no change needed).

Validation:
- go test ./sw-block/bridge/blockvol/... → PASS (10 tests)
- go test ./weed/storage/blockvol/v2bridge/ -run "TestControl_|TestBridge_" → PASS (7 tests)
- go test ./weed/server/ -run "TestBlockService_ApplyAssignments_RebuildingRole_" → PASS

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

weed/storage/blockvol/v2bridge/control.go

@@ -8,7 +8,6 @@
 package v2bridge
 
 import (
-	"fmt"
 	"log"
 
 	bridge "github.com/seaweedfs/seaweedfs/sw-block/bridge/blockvol"
@@ -85,35 +84,26 @@ func (cb *ControlBridge) convertPrimaryAssignment(a blockvol.BlockVolumeAssignme
 }
 
 func (cb *ControlBridge) convertReplicaAssignment(a blockvol.BlockVolumeAssignment, volumeName, localServerID string) engine.AssignmentIntent {
+	replica := bridge.ReplicaAssignmentForServer(volumeName, localServerID, engine.Endpoint{
+		DataAddr: a.ReplicaDataAddr,
+		CtrlAddr: a.ReplicaCtrlAddr,
+	})
 	return engine.AssignmentIntent{
-		Epoch: a.Epoch,
-		Replicas: []engine.ReplicaAssignment{
-			{
-				ReplicaID: fmt.Sprintf("%s/%s", volumeName, localServerID),
-				Endpoint: engine.Endpoint{
-					DataAddr: a.ReplicaDataAddr,
-					CtrlAddr: a.ReplicaCtrlAddr,
-				},
-			},
-		},
+		Epoch:    a.Epoch,
+		Replicas: []engine.ReplicaAssignment{replica},
 	}
 }
 
 func (cb *ControlBridge) convertRebuildAssignment(a blockvol.BlockVolumeAssignment, volumeName, localServerID string) engine.AssignmentIntent {
-	replicaID := fmt.Sprintf("%s/%s", volumeName, localServerID)
+	replica := bridge.ReplicaAssignmentForServer(volumeName, localServerID, engine.Endpoint{
+		DataAddr: a.ReplicaDataAddr,
+		CtrlAddr: a.ReplicaCtrlAddr,
+	})
 	return engine.AssignmentIntent{
-		Epoch: a.Epoch,
-		Replicas: []engine.ReplicaAssignment{
-			{
-				ReplicaID: replicaID,
-				Endpoint: engine.Endpoint{
-					DataAddr: a.ReplicaDataAddr,
-					CtrlAddr: a.ReplicaCtrlAddr,
-				},
-			},
-		},
+		Epoch:    a.Epoch,
+		Replicas: []engine.ReplicaAssignment{replica},
 		RecoveryTargets: map[string]engine.SessionKind{
-			replicaID: engine.SessionRebuild,
+			replica.ReplicaID: bridge.RecoveryTargetForRole("rebuilding"),
 		},
 	}
 }