diff --git a/packages/orchestrator/orchestrator.proto b/packages/orchestrator/orchestrator.proto
index 227a2665ee..c3fd6db6cb 100644
--- a/packages/orchestrator/orchestrator.proto
+++ b/packages/orchestrator/orchestrator.proto
@@ -128,9 +128,10 @@ message SandboxPauseRequest {
 }
 
 message SchedulingMetadata {
-  // base_build_id is the root layer (shared across the template's sandboxes);
-  // build_id is the final/current layer. Both also appear in the lists below.
-  string base_build_id = 1;
+  // memfile_base_build_id / rootfs_base_build_id are each artifact's root layer
+  // (shared across the template's sandboxes); they can differ. build_id is the
+  // final/current layer. All also appear in the lists below.
+  string memfile_base_build_id = 1;
   string build_id = 2;
   // Deduplicated build IDs whose data each artifact references (all ancestor
   // layers plus the build itself). Sorted; order is not significant. When a
@@ -144,6 +145,7 @@ message SchedulingMetadata {
   // new memfile layer's bytes are a pre-dedup, block-granular upper bound.
   repeated uint64 memfile_build_bytes = 7;
   repeated uint64 rootfs_build_bytes = 8;
+  string rootfs_base_build_id = 9;
 }
 
 message SandboxPauseResponse {
diff --git a/packages/orchestrator/pkg/scheduling/metadata.go b/packages/orchestrator/pkg/scheduling/metadata.go
index 01f3f0bbb2..de6111ef4f 100644
--- a/packages/orchestrator/pkg/scheduling/metadata.go
+++ b/packages/orchestrator/pkg/scheduling/metadata.go
@@ -25,16 +25,15 @@ func FromHeaders(buildID uuid.UUID, memfileHeader, rootfsHeader *header.Header,
 		return nil
 	}
 
-	base := memfileHeader.Metadata.BaseBuildId
-	if base == uuid.Nil {
-		base = rootfsHeader.Metadata.BaseBuildId
-	}
+	memfileBase := memfileHeader.Metadata.BaseBuildId
+	rootfsBase := rootfsHeader.Metadata.BaseBuildId
 
-	memIDs, memBytes, memDropped := artifactBuilds(memfileHeader, base, buildID, newMemfileBytes)
-	rootIDs, rootBytes, rootDropped := artifactBuilds(rootfsHeader, base, buildID, 0)
+	memIDs, memBytes, memDropped := artifactBuilds(memfileHeader, memfileBase, buildID, newMemfileBytes)
+	rootIDs, rootBytes, rootDropped := artifactBuilds(rootfsHeader, rootfsBase, buildID, 0)
 
 	return &orchestrator.SchedulingMetadata{
-		BaseBuildId:          base.String(),
+		MemfileBaseBuildId:   memfileBase.String(),
+		RootfsBaseBuildId:    rootfsBase.String(),
 		BuildId:              buildID.String(),
 		MemfileBuildIds:      memIDs,
 		RootfsBuildIds:       rootIDs,
diff --git a/packages/shared/pkg/grpc/orchestrator/orchestrator.pb.go b/packages/shared/pkg/grpc/orchestrator/orchestrator.pb.go
index d725a42e06..29e3c041bc 100644
--- a/packages/shared/pkg/grpc/orchestrator/orchestrator.pb.go
+++ b/packages/shared/pkg/grpc/orchestrator/orchestrator.pb.go
@@ -1015,10 +1015,11 @@ type SchedulingMetadata struct {
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	// base_build_id is the root layer (shared across the template's sandboxes);
-	// build_id is the final/current layer. Both also appear in the lists below.
-	BaseBuildId string `protobuf:"bytes,1,opt,name=base_build_id,json=baseBuildId,proto3" json:"base_build_id,omitempty"`
-	BuildId     string `protobuf:"bytes,2,opt,name=build_id,json=buildId,proto3" json:"build_id,omitempty"`
+	// memfile_base_build_id / rootfs_base_build_id are each artifact's root layer
+	// (shared across the template's sandboxes); they can differ. build_id is the
+	// final/current layer. All also appear in the lists below.
+	MemfileBaseBuildId string `protobuf:"bytes,1,opt,name=memfile_base_build_id,json=memfileBaseBuildId,proto3" json:"memfile_base_build_id,omitempty"`
+	BuildId            string `protobuf:"bytes,2,opt,name=build_id,json=buildId,proto3" json:"build_id,omitempty"`
 	// Deduplicated build IDs whose data each artifact references (all ancestor
 	// layers plus the build itself). Sorted; order is not significant. When a
 	// list exceeds the cap, the lightest layers are dropped first and the count
@@ -1031,6 +1032,7 @@ type SchedulingMetadata struct {
 	// new memfile layer's bytes are a pre-dedup, block-granular upper bound.
 	MemfileBuildBytes []uint64 `protobuf:"varint,7,rep,packed,name=memfile_build_bytes,json=memfileBuildBytes,proto3" json:"memfile_build_bytes,omitempty"`
 	RootfsBuildBytes  []uint64 `protobuf:"varint,8,rep,packed,name=rootfs_build_bytes,json=rootfsBuildBytes,proto3" json:"rootfs_build_bytes,omitempty"`
+	RootfsBaseBuildId string   `protobuf:"bytes,9,opt,name=rootfs_base_build_id,json=rootfsBaseBuildId,proto3" json:"rootfs_base_build_id,omitempty"`
 }
 
 func (x *SchedulingMetadata) Reset() {
@@ -1065,9 +1067,9 @@ func (*SchedulingMetadata) Descriptor() ([]byte, []int) {
 	return file_orchestrator_proto_rawDescGZIP(), []int{14}
 }
 
-func (x *SchedulingMetadata) GetBaseBuildId() string {
+func (x *SchedulingMetadata) GetMemfileBaseBuildId() string {
 	if x != nil {
-		return x.BaseBuildId
+		return x.MemfileBaseBuildId
 	}
 	return ""
 }
@@ -1121,6 +1123,13 @@ func (x *SchedulingMetadata) GetRootfsBuildBytes() []uint64 {
 	return nil
 }
 
+func (x *SchedulingMetadata) GetRootfsBaseBuildId() string {
+	if x != nil {
+		return x.RootfsBaseBuildId
+	}
+	return ""
+}
+
 type SandboxPauseResponse struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -1689,31 +1698,35 @@ var file_orchestrator_proto_rawDesc = []byte{
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