diff --git a/weed/pb/volume_server.proto b/weed/pb/volume_server.proto
index 74394dbdc..ff01027a8 100644
--- a/weed/pb/volume_server.proto
+++ b/weed/pb/volume_server.proto
@@ -455,6 +455,7 @@ message VolumeEcShardsDeleteRequest {
     bool full_teardown = 4; // pre-encode cleanup: wipe every EC artifact + generation for this volume, not just shard_ids
 }
 message VolumeEcShardsDeleteResponse {
+    bool full_teardown_done = 1; // set by a new server that performed full_teardown; absent from an old server lets the caller detect the silent no-op
 }
 
 message VolumeEcShardsMountRequest {
diff --git a/weed/pb/volume_server_pb/volume_server.pb.go b/weed/pb/volume_server_pb/volume_server.pb.go
index 0ee561708..2cc21a31f 100644
--- a/weed/pb/volume_server_pb/volume_server.pb.go
+++ b/weed/pb/volume_server_pb/volume_server.pb.go
@@ -3669,9 +3669,10 @@ func (x *VolumeEcShardsDeleteRequest) GetFullTeardown() bool {
 }
 
 type VolumeEcShardsDeleteResponse struct {
-	state         protoimpl.MessageState `protogen:"open.v1"`
-	unknownFields protoimpl.UnknownFields
-	sizeCache     protoimpl.SizeCache
+	state            protoimpl.MessageState `protogen:"open.v1"`
+	FullTeardownDone bool                   `protobuf:"varint,1,opt,name=full_teardown_done,json=fullTeardownDone,proto3" json:"full_teardown_done,omitempty"` // set by a new server that performed full_teardown; absent from an old server lets the caller detect the silent no-op
+	unknownFields    protoimpl.UnknownFields
+	sizeCache        protoimpl.SizeCache
 }
 
 func (x *VolumeEcShardsDeleteResponse) Reset() {
@@ -3704,6 +3705,13 @@ func (*VolumeEcShardsDeleteResponse) Descriptor() ([]byte, []int) {
 	return file_volume_server_proto_rawDescGZIP(), []int{65}
 }
 
+func (x *VolumeEcShardsDeleteResponse) GetFullTeardownDone() bool {
+	if x != nil {
+		return x.FullTeardownDone
+	}
+	return false
+}
+
 type VolumeEcShardsMountRequest struct {
 	state          protoimpl.MessageState `protogen:"open.v1"`
 	VolumeId       uint32                 `protobuf:"varint,1,opt,name=volume_id,json=volumeId,proto3" json:"volume_id,omitempty"`
@@ -7259,8 +7267,9 @@ const file_volume_server_proto_rawDesc = "" +
 	"collection\x18\x02 \x01(\tR\n" +
 	"collection\x12\x1b\n" +
 	"\tshard_ids\x18\x03 \x03(\rR\bshardIds\x12#\n" +
-	"\rfull_teardown\x18\x04 \x01(\bR\ffullTeardown\"\x1e\n" +
-	"\x1cVolumeEcShardsDeleteResponse\"\xa0\x01\n" +
+	"\rfull_teardown\x18\x04 \x01(\bR\ffullTeardown\"L\n" +
+	"\x1cVolumeEcShardsDeleteResponse\x12,\n" +
+	"\x12full_teardown_done\x18\x01 \x01(\bR\x10fullTeardownDone\"\xa0\x01\n" +
 	"\x1aVolumeEcShardsMountRequest\x12\x1b\n" +
 	"\tvolume_id\x18\x01 \x01(\rR\bvolumeId\x12\x1e\n" +
 	"\n" +
diff --git a/weed/server/volume_grpc_erasure_coding.go b/weed/server/volume_grpc_erasure_coding.go
index 126e41729..cd9cdbfa6 100644
--- a/weed/server/volume_grpc_erasure_coding.go
+++ b/weed/server/volume_grpc_erasure_coding.go
@@ -431,7 +431,7 @@ func (vs *VolumeServer) VolumeEcShardsDelete(ctx context.Context, req *volume_se
 				return nil, fmt.Errorf("full teardown of ec volume %d on %s: %w", req.VolumeId, location.Directory, err)
 			}
 		}
-		return &volume_server_pb.VolumeEcShardsDeleteResponse{}, nil
+		return &volume_server_pb.VolumeEcShardsDeleteResponse{FullTeardownDone: true}, nil
 	}
 
 	glog.V(0).Infof("ec volume %s shard delete %v", bName, req.ShardIds)
diff --git a/weed/shell/command_ec_common.go b/weed/shell/command_ec_common.go
index 7afc21cd6..c0c709365 100644
--- a/weed/shell/command_ec_common.go
+++ b/weed/shell/command_ec_common.go
@@ -2,6 +2,7 @@ package shell
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"regexp"
 	"slices"
@@ -536,6 +537,13 @@ func sourceServerDeleteEcShards(grpcDialOption grpc.DialOption, collection strin
 
 }
 
+// errFullTeardownNotAcked marks a VolumeEcShardsDelete whose server did not
+// echo full_teardown_done -- a pre-upgrade volume server silently ignoring the
+// flag. The pre-encode sweep treats it as fatal only for a reported (mounted)
+// leftover; for an unreported node it is best-effort, since that node likely had
+// nothing to wipe and an old server cannot acknowledge either way.
+var errFullTeardownNotAcked = errors.New("volume server did not perform full teardown")
+
 // unmountAndDeleteEcShardsQuiet unmounts then deletes shards on one server in a
 // single connection, without the per-call logging the interactive helpers emit.
 // Used by the orphan sweep, which fans out to every node x volume and would
@@ -549,14 +557,18 @@ func unmountAndDeleteEcShardsQuiet(grpcDialOption grpc.DialOption, collection st
 		}); err != nil {
 			return fmt.Errorf("unmount: %w", err)
 		}
-		if _, err := volumeServerClient.VolumeEcShardsDelete(context.Background(), &volume_server_pb.VolumeEcShardsDeleteRequest{
+		resp, err := volumeServerClient.VolumeEcShardsDelete(context.Background(), &volume_server_pb.VolumeEcShardsDeleteRequest{
 			VolumeId:     uint32(volumeId),
 			Collection:   collection,
 			ShardIds:     ids,
 			FullTeardown: true,
-		}); err != nil {
+		})
+		if err != nil {
 			return fmt.Errorf("delete: %w", err)
 		}
+		if !resp.GetFullTeardownDone() {
+			return fmt.Errorf("delete on %s: %w", location, errFullTeardownNotAcked)
+		}
 		return nil
 	})
 }
diff --git a/weed/shell/command_ec_encode.go b/weed/shell/command_ec_encode.go
index a91aab188..f5918adee 100644
--- a/weed/shell/command_ec_encode.go
+++ b/weed/shell/command_ec_encode.go
@@ -2,6 +2,7 @@ package shell
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -405,12 +406,14 @@ func clearPreexistingEcShards(commandEnv *CommandEnv, topologyInfo *master_pb.To
 			ewg.Add(func() error {
 				if err := unmountAndDeleteEcShardsQuiet(commandEnv.option.GrpcDialOption, collection, vid, addr, allShardIds); err != nil {
 					// Surface a reachable node whose delete genuinely failed (its orphan would
-					// be re-stamped by a later copy installing the new .vif); stay best-effort
-					// only for an unreachable node, which cannot receive this new generation.
-					if fatal || !isNodeUnreachable(err) {
+					// be re-stamped by a later copy installing the new .vif). Stay best-effort
+					// for an unreachable node (it cannot receive this new generation) and for
+					// a pre-upgrade node that did not ack full_teardown on an UNREPORTED pair
+					// (it likely had nothing to wipe); a reported leftover stays fatal.
+					if fatal || (!isNodeUnreachable(err) && !errors.Is(err, errFullTeardownNotAcked)) {
 						return fmt.Errorf("clear stale ec shards for volume %d on %s: %w", vid, addr, err)
 					}
-					glog.V(1).Infof("orphan sweep: volume %d on %s unreachable, skipping: %v", vid, addr, err)
+					glog.V(1).Infof("orphan sweep: volume %d on %s skipped: %v", vid, addr, err)
 				}
 				return nil
 			})
diff --git a/weed/worker/tasks/erasure_coding/ec_task.go b/weed/worker/tasks/erasure_coding/ec_task.go
index fcc5921f5..7bdf201f5 100644
--- a/weed/worker/tasks/erasure_coding/ec_task.go
+++ b/weed/worker/tasks/erasure_coding/ec_task.go
@@ -977,14 +977,18 @@ func unmountAndDeleteEcShards(
 			}); err != nil {
 				return fmt.Errorf("unmount: %w", err)
 			}
-			if _, err := client.VolumeEcShardsDelete(ctx, &volume_server_pb.VolumeEcShardsDeleteRequest{
+			resp, err := client.VolumeEcShardsDelete(ctx, &volume_server_pb.VolumeEcShardsDeleteRequest{
 				VolumeId:     volumeID,
 				Collection:   collection,
 				ShardIds:     shardIds,
 				FullTeardown: true,
-			}); err != nil {
+			})
+			if err != nil {
 				return fmt.Errorf("delete: %w", err)
 			}
+			if !resp.GetFullTeardownDone() {
+				return fmt.Errorf("delete: %s did not perform full teardown (pre-upgrade volume server?); a stale EC generation may remain", destination)
+			}
 			return nil
 		})
 }