diff --git a/internal/server/mock/trace/stream_traces.go b/internal/server/mock/trace/stream_traces.go
index 09da708..8c1c488 100644
--- a/internal/server/mock/trace/stream_traces.go
+++ b/internal/server/mock/trace/stream_traces.go
@@ -20,32 +20,63 @@ func (s *Server) StreamTraces(_ *pb.StreamTracesRequest, server pb.Trace_StreamT
 		// ~6ms realistic function execution time
 		latency := 6 * time.Millisecond
 
-		// Function calls generator with Duration + timestamp
-		makeFunctionCalls := func(base time.Time) []*pb.TraceFunctionCall {
+		// Function calls generator, placed relative to the start of the request.
+		makeFunctionCalls := func() []*pb.TraceFunctionCall {
 			return []*pb.TraceFunctionCall{
 				{
-					Name:      "PDOStatement::execute",
-					StartTime: timestamppb.New(base),
-					Elapsed:   durationpb.New(latency),
+					Name:    "PDOStatement::execute",
+					Offset:  durationpb.New(0),
+					Elapsed: durationpb.New(latency),
+					Memory:  1048576,
 				},
 				{
-					Name:      "Drupal\\Core\\Database\\StatementPrefetchIterator::execute",
-					StartTime: timestamppb.New(base.Add(500 * time.Microsecond)),
-					Elapsed:   durationpb.New(latency),
+					Name:    "Drupal\\Core\\Database\\StatementPrefetchIterator::execute",
+					Offset:  durationpb.New(500 * time.Microsecond),
+					Elapsed: durationpb.New(latency),
+					Memory:  2097152,
 				},
 				{
-					Name:      "Drupal\\sqlite\\Driver\\Database\\sqlite\\Statement::execute",
-					StartTime: timestamppb.New(base.Add(1 * time.Millisecond)),
-					Elapsed:   durationpb.New(latency),
+					Name:    "Drupal\\sqlite\\Driver\\Database\\sqlite\\Statement::execute",
+					Offset:  durationpb.New(1 * time.Millisecond),
+					Elapsed: durationpb.New(latency),
+					Memory:  524288,
 				},
 				{
-					Name:      "Drupal\\Core\\Database\\Query\\Upsert::execute",
-					StartTime: timestamppb.New(base.Add(1500 * time.Microsecond)),
-					Elapsed:   durationpb.New(latency),
+					Name:    "Drupal\\Core\\Database\\Query\\Upsert::execute",
+					Offset:  durationpb.New(1500 * time.Microsecond),
+					Elapsed: durationpb.New(latency),
+					Memory:  786432,
 				},
 			}
 		}
 
+		makeDrupal := func() *pb.TraceDrupal {
+			return &pb.TraceDrupal{
+				CacheEvents: []*pb.TraceDrupalCacheEvent{
+					{
+						Origin:   pb.TraceDrupalCacheOrigin_TRACE_DRUPAL_CACHE_ORIGIN_RENDER_ARRAY,
+						Caller:   "Drupal\\Core\\Render\\Renderer::doRender",
+						MaxAge:   -1,
+						Tags:     []string{"node:1", "node_list"},
+						Contexts: []string{"url.path", "user.permissions"},
+						Offset:   durationpb.New(2 * time.Millisecond),
+						Calls:    12,
+					},
+					{
+						Origin:     pb.TraceDrupalCacheOrigin_TRACE_DRUPAL_CACHE_ORIGIN_OBJECT,
+						Caller:     "Drupal\\Core\\Cache\\CacheableMetadata::createFromObject",
+						ObjectType: "Drupal\\node\\Entity\\Node",
+						MaxAge:     3600,
+						Tags:       []string{"node:1"},
+						Contexts:   []string{"user.roles"},
+						Offset:     durationpb.New(4 * time.Millisecond),
+						Calls:      3,
+					},
+				},
+				CacheEventsDropped: 0,
+			}
+		}
+
 		// Create 3 traces with increasing offsets
 		traces := make([]*pb.Trace, 0, 3)
 
@@ -56,12 +87,20 @@ func (s *Server) StreamTraces(_ *pb.StreamTracesRequest, server pb.Trace_StreamT
 			traces = append(traces, &pb.Trace{
 				Metadata: &pb.TraceMetadata{
 					RequestId: gofakeit.UUID(),
-					Method:    http.MethodGet,
-					Uri:       "/sites/default/files/styles/scale_crop_7_3_wide/public/veggie-pasta-bake-hero-umami.jpg.webp?itok=CYsHBUlX",
 					StartTime: timestamppb.New(start),
 					EndTime:   timestamppb.New(end),
+					Source:    pb.TraceSource_TRACE_SOURCE_HTTP,
+					Runtime:   pb.TraceRuntime_TRACE_RUNTIME_PHP,
+					Http: &pb.TraceMetadataHTTP{
+						Method: http.MethodGet,
+						Uri:    "/sites/default/files/styles/scale_crop_7_3_wide/public/veggie-pasta-bake-hero-umami.jpg.webp?itok=CYsHBUlX",
+					},
+				},
+				FunctionCalls: makeFunctionCalls(),
+				ResourceUtilisation: &pb.TraceResourceUtilisation{
+					MaxMemory: 33554432,
 				},
-				FunctionCalls: makeFunctionCalls(start),
+				Drupal: makeDrupal(),
 			})
 		}
 
diff --git a/pb/trace.pb.go b/pb/trace.pb.go
index 9ade859..d867476 100644
--- a/pb/trace.pb.go
+++ b/pb/trace.pb.go
@@ -24,6 +24,156 @@ const (
 	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
 )
 
+// The invocation mechanism which produced the trace.
+type TraceSource int32
+
+const (
+	TraceSource_TRACE_SOURCE_UNSPECIFIED TraceSource = 0
+	TraceSource_TRACE_SOURCE_HTTP        TraceSource = 1 // Trace was collected from a HTTP request.
+	TraceSource_TRACE_SOURCE_CLI         TraceSource = 2 // Trace was collected from the command line interface.
+)
+
+// Enum value maps for TraceSource.
+var (
+	TraceSource_name = map[int32]string{
+		0: "TRACE_SOURCE_UNSPECIFIED",
+		1: "TRACE_SOURCE_HTTP",
+		2: "TRACE_SOURCE_CLI",
+	}
+	TraceSource_value = map[string]int32{
+		"TRACE_SOURCE_UNSPECIFIED": 0,
+		"TRACE_SOURCE_HTTP":        1,
+		"TRACE_SOURCE_CLI":         2,
+	}
+)
+
+func (x TraceSource) Enum() *TraceSource {
+	p := new(TraceSource)
+	*p = x
+	return p
+}
+
+func (x TraceSource) String() string {
+	return protoimpl.X.EnumStringOf(x.Descriptor(), protoreflect.EnumNumber(x))
+}
+
+func (TraceSource) Descriptor() protoreflect.EnumDescriptor {
+	return file_trace_proto_enumTypes[0].Descriptor()
+}
+
+func (TraceSource) Type() protoreflect.EnumType {
+	return &file_trace_proto_enumTypes[0]
+}
+
+func (x TraceSource) Number() protoreflect.EnumNumber {
+	return protoreflect.EnumNumber(x)
+}
+
+// Deprecated: Use TraceSource.Descriptor instead.
+func (TraceSource) EnumDescriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{0}
+}
+
+// The language runtime which produced the trace.
+type TraceRuntime int32
+
+const (
+	TraceRuntime_TRACE_RUNTIME_UNSPECIFIED TraceRuntime = 0
+	TraceRuntime_TRACE_RUNTIME_PHP         TraceRuntime = 1 // Trace was collected from a PHP process.
+	TraceRuntime_TRACE_RUNTIME_NODE        TraceRuntime = 2 // Trace was collected from a Node.js process.
+)
+
+// Enum value maps for TraceRuntime.
+var (
+	TraceRuntime_name = map[int32]string{
+		0: "TRACE_RUNTIME_UNSPECIFIED",
+		1: "TRACE_RUNTIME_PHP",
+		2: "TRACE_RUNTIME_NODE",
+	}
+	TraceRuntime_value = map[string]int32{
+		"TRACE_RUNTIME_UNSPECIFIED": 0,
+		"TRACE_RUNTIME_PHP":         1,
+		"TRACE_RUNTIME_NODE":        2,
+	}
+)
+
+func (x TraceRuntime) Enum() *TraceRuntime {
+	p := new(TraceRuntime)
+	*p = x
+	return p
+}
+
+func (x TraceRuntime) String() string {
+	return protoimpl.X.EnumStringOf(x.Descriptor(), protoreflect.EnumNumber(x))
+}
+
+func (TraceRuntime) Descriptor() protoreflect.EnumDescriptor {
+	return file_trace_proto_enumTypes[1].Descriptor()
+}
+
+func (TraceRuntime) Type() protoreflect.EnumType {
+	return &file_trace_proto_enumTypes[1]
+}
+
+func (x TraceRuntime) Number() protoreflect.EnumNumber {
+	return protoreflect.EnumNumber(x)
+}
+
+// Deprecated: Use TraceRuntime.Descriptor instead.
+func (TraceRuntime) EnumDescriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{1}
+}
+
+// Which Drupal API produced a cache event.
+type TraceDrupalCacheOrigin int32
+
+const (
+	TraceDrupalCacheOrigin_TRACE_DRUPAL_CACHE_ORIGIN_UNSPECIFIED  TraceDrupalCacheOrigin = 0
+	TraceDrupalCacheOrigin_TRACE_DRUPAL_CACHE_ORIGIN_RENDER_ARRAY TraceDrupalCacheOrigin = 1 // Cacheability was collected from a render array.
+	TraceDrupalCacheOrigin_TRACE_DRUPAL_CACHE_ORIGIN_OBJECT       TraceDrupalCacheOrigin = 2 // Cacheability was collected from an object.
+)
+
+// Enum value maps for TraceDrupalCacheOrigin.
+var (
+	TraceDrupalCacheOrigin_name = map[int32]string{
+		0: "TRACE_DRUPAL_CACHE_ORIGIN_UNSPECIFIED",
+		1: "TRACE_DRUPAL_CACHE_ORIGIN_RENDER_ARRAY",
+		2: "TRACE_DRUPAL_CACHE_ORIGIN_OBJECT",
+	}
+	TraceDrupalCacheOrigin_value = map[string]int32{
+		"TRACE_DRUPAL_CACHE_ORIGIN_UNSPECIFIED":  0,
+		"TRACE_DRUPAL_CACHE_ORIGIN_RENDER_ARRAY": 1,
+		"TRACE_DRUPAL_CACHE_ORIGIN_OBJECT":       2,
+	}
+)
+
+func (x TraceDrupalCacheOrigin) Enum() *TraceDrupalCacheOrigin {
+	p := new(TraceDrupalCacheOrigin)
+	*p = x
+	return p
+}
+
+func (x TraceDrupalCacheOrigin) String() string {
+	return protoimpl.X.EnumStringOf(x.Descriptor(), protoreflect.EnumNumber(x))
+}
+
+func (TraceDrupalCacheOrigin) Descriptor() protoreflect.EnumDescriptor {
+	return file_trace_proto_enumTypes[2].Descriptor()
+}
+
+func (TraceDrupalCacheOrigin) Type() protoreflect.EnumType {
+	return &file_trace_proto_enumTypes[2]
+}
+
+func (x TraceDrupalCacheOrigin) Number() protoreflect.EnumNumber {
+	return protoreflect.EnumNumber(x)
+}
+
+// Deprecated: Use TraceDrupalCacheOrigin.Descriptor instead.
+func (TraceDrupalCacheOrigin) EnumDescriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{2}
+}
+
 // *
 // Input for StreamTraces.
 type StreamTracesRequest struct {
@@ -129,8 +279,10 @@ type Trace struct {
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	Metadata      *TraceMetadata       `protobuf:"bytes,1,opt,name=metadata,proto3" json:"metadata,omitempty"`                                // Metadata about the trace.
-	FunctionCalls []*TraceFunctionCall `protobuf:"bytes,2,rep,name=function_calls,json=functionCalls,proto3" json:"function_calls,omitempty"` // List of function calls in the trace.
+	Metadata            *TraceMetadata            `protobuf:"bytes,1,opt,name=metadata,proto3" json:"metadata,omitempty"`                                                  // Metadata about the trace.
+	FunctionCalls       []*TraceFunctionCall      `protobuf:"bytes,2,rep,name=function_calls,json=functionCalls,proto3" json:"function_calls,omitempty"`                   // List of function calls in the trace.
+	ResourceUtilisation *TraceResourceUtilisation `protobuf:"bytes,3,opt,name=resource_utilisation,json=resourceUtilisation,proto3" json:"resource_utilisation,omitempty"` // Resources consumed by the request.
+	Drupal              *TraceDrupal              `protobuf:"bytes,4,opt,name=drupal,proto3,oneof" json:"drupal,omitempty"`                                                // Drupal specific data. Only populated for PHP traces which called into the Drupal APIs.
 }
 
 func (x *Trace) Reset() {
@@ -179,6 +331,20 @@ func (x *Trace) GetFunctionCalls() []*TraceFunctionCall {
 	return nil
 }
 
+func (x *Trace) GetResourceUtilisation() *TraceResourceUtilisation {
+	if x != nil {
+		return x.ResourceUtilisation
+	}
+	return nil
+}
+
+func (x *Trace) GetDrupal() *TraceDrupal {
+	if x != nil {
+		return x.Drupal
+	}
+	return nil
+}
+
 // *
 // Metadata which contains information about the trace.
 type TraceMetadata struct {
@@ -186,11 +352,19 @@ type TraceMetadata struct {
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	RequestId string                 `protobuf:"bytes,1,opt,name=request_id,json=requestId,proto3" json:"request_id,omitempty"` // Request identifier for tracking.
-	Uri       string                 `protobuf:"bytes,2,opt,name=uri,proto3" json:"uri,omitempty"`                              // URI of the request being traced.
-	Method    string                 `protobuf:"bytes,3,opt,name=method,proto3" json:"method,omitempty"`                        // HTTP method of the request (e.g., GET, POST).
-	StartTime *timestamppb.Timestamp `protobuf:"bytes,4,opt,name=start_time,json=startTime,proto3" json:"start_time,omitempty"` // Start time of the trace in unix format.
-	EndTime   *timestamppb.Timestamp `protobuf:"bytes,5,opt,name=end_time,json=endTime,proto3" json:"end_time,omitempty"`       // End time of the trace in unix format.
+	// Request identifier for tracking.
+	//
+	// Compass sends "UNKNOWN" when the request carried no HTTP_X_REQUEST_ID
+	// header. That is a sentinel, not an identifier: two traces reading UNKNOWN
+	// are not the same request, so anything correlating on this must treat it as
+	// absent.
+	RequestId string                 `protobuf:"bytes,1,opt,name=request_id,json=requestId,proto3" json:"request_id,omitempty"`
+	StartTime *timestamppb.Timestamp `protobuf:"bytes,2,opt,name=start_time,json=startTime,proto3" json:"start_time,omitempty"`        // Start time of the trace.
+	EndTime   *timestamppb.Timestamp `protobuf:"bytes,3,opt,name=end_time,json=endTime,proto3" json:"end_time,omitempty"`              // End time of the trace.
+	Source    TraceSource            `protobuf:"varint,4,opt,name=source,proto3,enum=workflow.TraceSource" json:"source,omitempty"`    // How the traced request was invoked.
+	Runtime   TraceRuntime           `protobuf:"varint,5,opt,name=runtime,proto3,enum=workflow.TraceRuntime" json:"runtime,omitempty"` // Language runtime which produced the trace.
+	Http      *TraceMetadataHTTP     `protobuf:"bytes,6,opt,name=http,proto3,oneof" json:"http,omitempty"`                             // Request details. Only set when source is TRACE_SOURCE_HTTP.
+	Cli       *TraceMetadataCLI      `protobuf:"bytes,7,opt,name=cli,proto3,oneof" json:"cli,omitempty"`                               // Command details. Only set when source is TRACE_SOURCE_CLI.
 }
 
 func (x *TraceMetadata) Reset() {
@@ -232,34 +406,203 @@ func (x *TraceMetadata) GetRequestId() string {
 	return ""
 }
 
-func (x *TraceMetadata) GetUri() string {
+func (x *TraceMetadata) GetStartTime() *timestamppb.Timestamp {
 	if x != nil {
-		return x.Uri
+		return x.StartTime
 	}
-	return ""
+	return nil
 }
 
-func (x *TraceMetadata) GetMethod() string {
+func (x *TraceMetadata) GetEndTime() *timestamppb.Timestamp {
 	if x != nil {
-		return x.Method
+		return x.EndTime
 	}
-	return ""
+	return nil
 }
 
-func (x *TraceMetadata) GetStartTime() *timestamppb.Timestamp {
+func (x *TraceMetadata) GetSource() TraceSource {
 	if x != nil {
-		return x.StartTime
+		return x.Source
+	}
+	return TraceSource_TRACE_SOURCE_UNSPECIFIED
+}
+
+func (x *TraceMetadata) GetRuntime() TraceRuntime {
+	if x != nil {
+		return x.Runtime
+	}
+	return TraceRuntime_TRACE_RUNTIME_UNSPECIFIED
+}
+
+func (x *TraceMetadata) GetHttp() *TraceMetadataHTTP {
+	if x != nil {
+		return x.Http
 	}
 	return nil
 }
 
-func (x *TraceMetadata) GetEndTime() *timestamppb.Timestamp {
+func (x *TraceMetadata) GetCli() *TraceMetadataCLI {
 	if x != nil {
-		return x.EndTime
+		return x.Cli
 	}
 	return nil
 }
 
+// *
+// Metadata for a trace which was invoked by a HTTP request.
+type TraceMetadataHTTP struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Method string `protobuf:"bytes,1,opt,name=method,proto3" json:"method,omitempty"` // HTTP method of the request (e.g., GET, POST).
+	Uri    string `protobuf:"bytes,2,opt,name=uri,proto3" json:"uri,omitempty"`       // URI of the request being traced.
+}
+
+func (x *TraceMetadataHTTP) Reset() {
+	*x = TraceMetadataHTTP{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_trace_proto_msgTypes[4]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *TraceMetadataHTTP) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*TraceMetadataHTTP) ProtoMessage() {}
+
+func (x *TraceMetadataHTTP) ProtoReflect() protoreflect.Message {
+	mi := &file_trace_proto_msgTypes[4]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use TraceMetadataHTTP.ProtoReflect.Descriptor instead.
+func (*TraceMetadataHTTP) Descriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{4}
+}
+
+func (x *TraceMetadataHTTP) GetMethod() string {
+	if x != nil {
+		return x.Method
+	}
+	return ""
+}
+
+func (x *TraceMetadataHTTP) GetUri() string {
+	if x != nil {
+		return x.Uri
+	}
+	return ""
+}
+
+// *
+// Metadata for a trace which was invoked from the command line.
+type TraceMetadataCLI struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Command string `protobuf:"bytes,1,opt,name=command,proto3" json:"command,omitempty"` // Command which was executed.
+}
+
+func (x *TraceMetadataCLI) Reset() {
+	*x = TraceMetadataCLI{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_trace_proto_msgTypes[5]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *TraceMetadataCLI) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*TraceMetadataCLI) ProtoMessage() {}
+
+func (x *TraceMetadataCLI) ProtoReflect() protoreflect.Message {
+	mi := &file_trace_proto_msgTypes[5]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use TraceMetadataCLI.ProtoReflect.Descriptor instead.
+func (*TraceMetadataCLI) Descriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{5}
+}
+
+func (x *TraceMetadataCLI) GetCommand() string {
+	if x != nil {
+		return x.Command
+	}
+	return ""
+}
+
+// *
+// Resources consumed over the course of the traced request.
+type TraceResourceUtilisation struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	MaxMemory int64 `protobuf:"varint,1,opt,name=max_memory,json=maxMemory,proto3" json:"max_memory,omitempty"` // Peak memory used by the request, in bytes.
+}
+
+func (x *TraceResourceUtilisation) Reset() {
+	*x = TraceResourceUtilisation{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_trace_proto_msgTypes[6]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *TraceResourceUtilisation) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*TraceResourceUtilisation) ProtoMessage() {}
+
+func (x *TraceResourceUtilisation) ProtoReflect() protoreflect.Message {
+	mi := &file_trace_proto_msgTypes[6]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use TraceResourceUtilisation.ProtoReflect.Descriptor instead.
+func (*TraceResourceUtilisation) Descriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{6}
+}
+
+func (x *TraceResourceUtilisation) GetMaxMemory() int64 {
+	if x != nil {
+		return x.MaxMemory
+	}
+	return 0
+}
+
 // *
 // Function call data within a trace.
 type TraceFunctionCall struct {
@@ -267,15 +610,16 @@ type TraceFunctionCall struct {
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	Name      string                 `protobuf:"bytes,1,opt,name=name,proto3" json:"name,omitempty"`                            // Name of the function being traced.
-	StartTime *timestamppb.Timestamp `protobuf:"bytes,2,opt,name=start_time,json=startTime,proto3" json:"start_time,omitempty"` // Start time of the function call in unix format.
-	Elapsed   *durationpb.Duration   `protobuf:"bytes,3,opt,name=elapsed,proto3" json:"elapsed,omitempty"`                      // Elapsed time for the function call in milliseconds.
+	Name    string               `protobuf:"bytes,1,opt,name=name,proto3" json:"name,omitempty"`       // Name of the function being traced.
+	Offset  *durationpb.Duration `protobuf:"bytes,2,opt,name=offset,proto3" json:"offset,omitempty"`   // Offset from the start of the request at which the call began.
+	Elapsed *durationpb.Duration `protobuf:"bytes,3,opt,name=elapsed,proto3" json:"elapsed,omitempty"` // How long the call ran for.
+	Memory  int64                `protobuf:"varint,4,opt,name=memory,proto3" json:"memory,omitempty"`  // Memory used by the call, in bytes.
 }
 
 func (x *TraceFunctionCall) Reset() {
 	*x = TraceFunctionCall{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_trace_proto_msgTypes[4]
+		mi := &file_trace_proto_msgTypes[7]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -288,7 +632,7 @@ func (x *TraceFunctionCall) String() string {
 func (*TraceFunctionCall) ProtoMessage() {}
 
 func (x *TraceFunctionCall) ProtoReflect() protoreflect.Message {
-	mi := &file_trace_proto_msgTypes[4]
+	mi := &file_trace_proto_msgTypes[7]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -301,7 +645,7 @@ func (x *TraceFunctionCall) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use TraceFunctionCall.ProtoReflect.Descriptor instead.
 func (*TraceFunctionCall) Descriptor() ([]byte, []int) {
-	return file_trace_proto_rawDescGZIP(), []int{4}
+	return file_trace_proto_rawDescGZIP(), []int{7}
 }
 
 func (x *TraceFunctionCall) GetName() string {
@@ -311,9 +655,9 @@ func (x *TraceFunctionCall) GetName() string {
 	return ""
 }
 
-func (x *TraceFunctionCall) GetStartTime() *timestamppb.Timestamp {
+func (x *TraceFunctionCall) GetOffset() *durationpb.Duration {
 	if x != nil {
-		return x.StartTime
+		return x.Offset
 	}
 	return nil
 }
@@ -325,6 +669,183 @@ func (x *TraceFunctionCall) GetElapsed() *durationpb.Duration {
 	return nil
 }
 
+func (x *TraceFunctionCall) GetMemory() int64 {
+	if x != nil {
+		return x.Memory
+	}
+	return 0
+}
+
+// *
+// Drupal specific data collected for a trace.
+//
+// Only populated for PHP traces where the application called into the Drupal
+// APIs which Compass probes, so it is absent for Node traces, PHP CLI traces
+// and non-Drupal PHP applications.
+type TraceDrupal struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	CacheEvents        []*TraceDrupalCacheEvent `protobuf:"bytes,1,rep,name=cache_events,json=cacheEvents,proto3" json:"cache_events,omitempty"`                         // Cache events which occurred during this trace, aggregated by their contents.
+	CacheEventsDropped int64                    `protobuf:"varint,2,opt,name=cache_events_dropped,json=cacheEventsDropped,proto3" json:"cache_events_dropped,omitempty"` // How many distinct cache events were discarded because the trace reached its retention limit. Reported so that a truncated trace is not mistaken for a complete one.
+}
+
+func (x *TraceDrupal) Reset() {
+	*x = TraceDrupal{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_trace_proto_msgTypes[8]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *TraceDrupal) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*TraceDrupal) ProtoMessage() {}
+
+func (x *TraceDrupal) ProtoReflect() protoreflect.Message {
+	mi := &file_trace_proto_msgTypes[8]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use TraceDrupal.ProtoReflect.Descriptor instead.
+func (*TraceDrupal) Descriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{8}
+}
+
+func (x *TraceDrupal) GetCacheEvents() []*TraceDrupalCacheEvent {
+	if x != nil {
+		return x.CacheEvents
+	}
+	return nil
+}
+
+func (x *TraceDrupal) GetCacheEventsDropped() int64 {
+	if x != nil {
+		return x.CacheEventsDropped
+	}
+	return 0
+}
+
+// *
+// Cacheability metadata that Drupal derived at a point in the request.
+//
+// Drupal derives cacheability far more often than a request has interesting
+// function calls, so identical events are aggregated into a single entry with a
+// call count rather than retained individually.
+type TraceDrupalCacheEvent struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Origin     TraceDrupalCacheOrigin `protobuf:"varint,1,opt,name=origin,proto3,enum=workflow.TraceDrupalCacheOrigin" json:"origin,omitempty"` // Origin of the cacheability metadata.
+	Caller     string                 `protobuf:"bytes,2,opt,name=caller,proto3" json:"caller,omitempty"`                                       // Caller which asked Drupal for the cacheability metadata.
+	ObjectType string                 `protobuf:"bytes,3,opt,name=object_type,json=objectType,proto3" json:"object_type,omitempty"`             // Type the metadata was derived from. Only set for TRACE_DRUPAL_CACHE_ORIGIN_OBJECT.
+	MaxAge     int64                  `protobuf:"varint,4,opt,name=max_age,json=maxAge,proto3" json:"max_age,omitempty"`                        // Max age in seconds, where -1 means cacheable forever.
+	Tags       []string               `protobuf:"bytes,5,rep,name=tags,proto3" json:"tags,omitempty"`                                           // Tags which the cached item is invalidated by.
+	Contexts   []string               `protobuf:"bytes,6,rep,name=contexts,proto3" json:"contexts,omitempty"`                                   // Contexts which the cached item varies by.
+	Offset     *durationpb.Duration   `protobuf:"bytes,7,opt,name=offset,proto3" json:"offset,omitempty"`                                       // Offset from the start of the request at which the first of these events occurred.
+	Calls      int64                  `protobuf:"varint,8,opt,name=calls,proto3" json:"calls,omitempty"`                                        // How many identical events were aggregated into this one.
+}
+
+func (x *TraceDrupalCacheEvent) Reset() {
+	*x = TraceDrupalCacheEvent{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_trace_proto_msgTypes[9]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *TraceDrupalCacheEvent) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*TraceDrupalCacheEvent) ProtoMessage() {}
+
+func (x *TraceDrupalCacheEvent) ProtoReflect() protoreflect.Message {
+	mi := &file_trace_proto_msgTypes[9]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use TraceDrupalCacheEvent.ProtoReflect.Descriptor instead.
+func (*TraceDrupalCacheEvent) Descriptor() ([]byte, []int) {
+	return file_trace_proto_rawDescGZIP(), []int{9}
+}
+
+func (x *TraceDrupalCacheEvent) GetOrigin() TraceDrupalCacheOrigin {
+	if x != nil {
+		return x.Origin
+	}
+	return TraceDrupalCacheOrigin_TRACE_DRUPAL_CACHE_ORIGIN_UNSPECIFIED
+}
+
+func (x *TraceDrupalCacheEvent) GetCaller() string {
+	if x != nil {
+		return x.Caller
+	}
+	return ""
+}
+
+func (x *TraceDrupalCacheEvent) GetObjectType() string {
+	if x != nil {
+		return x.ObjectType
+	}
+	return ""
+}
+
+func (x *TraceDrupalCacheEvent) GetMaxAge() int64 {
+	if x != nil {
+		return x.MaxAge
+	}
+	return 0
+}
+
+func (x *TraceDrupalCacheEvent) GetTags() []string {
+	if x != nil {
+		return x.Tags
+	}
+	return nil
+}
+
+func (x *TraceDrupalCacheEvent) GetContexts() []string {
+	if x != nil {
+		return x.Contexts
+	}
+	return nil
+}
+
+func (x *TraceDrupalCacheEvent) GetOffset() *durationpb.Duration {
+	if x != nil {
+		return x.Offset
+	}
+	return nil
+}
+
+func (x *TraceDrupalCacheEvent) GetCalls() int64 {
+	if x != nil {
+		return x.Calls
+	}
+	return 0
+}
+
 var File_trace_proto protoreflect.FileDescriptor
 
 var file_trace_proto_rawDesc = []byte{
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+	0x2e, 0x2f, 0x70, 0x62, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
@@ -393,31 +993,49 @@ func file_trace_proto_rawDescGZIP() []byte {
 	return file_trace_proto_rawDescData
 }
 
-var file_trace_proto_msgTypes = make([]protoimpl.MessageInfo, 5)
+var file_trace_proto_enumTypes = make([]protoimpl.EnumInfo, 3)
+var file_trace_proto_msgTypes = make([]protoimpl.MessageInfo, 10)
 var file_trace_proto_goTypes = []interface{}{
-	(*StreamTracesRequest)(nil),   // 0: workflow.StreamTracesRequest
-	(*StreamTracesResponse)(nil),  // 1: workflow.StreamTracesResponse
-	(*Trace)(nil),                 // 2: workflow.Trace
-	(*TraceMetadata)(nil),         // 3: workflow.TraceMetadata
-	(*TraceFunctionCall)(nil),     // 4: workflow.TraceFunctionCall
-	(*timestamppb.Timestamp)(nil), // 5: google.protobuf.Timestamp
-	(*durationpb.Duration)(nil),   // 6: google.protobuf.Duration
+	(TraceSource)(0),                 // 0: workflow.TraceSource
+	(TraceRuntime)(0),                // 1: workflow.TraceRuntime
+	(TraceDrupalCacheOrigin)(0),      // 2: workflow.TraceDrupalCacheOrigin
+	(*StreamTracesRequest)(nil),      // 3: workflow.StreamTracesRequest
+	(*StreamTracesResponse)(nil),     // 4: workflow.StreamTracesResponse
+	(*Trace)(nil),                    // 5: workflow.Trace
+	(*TraceMetadata)(nil),            // 6: workflow.TraceMetadata
+	(*TraceMetadataHTTP)(nil),        // 7: workflow.TraceMetadataHTTP
+	(*TraceMetadataCLI)(nil),         // 8: workflow.TraceMetadataCLI
+	(*TraceResourceUtilisation)(nil), // 9: workflow.TraceResourceUtilisation
+	(*TraceFunctionCall)(nil),        // 10: workflow.TraceFunctionCall
+	(*TraceDrupal)(nil),              // 11: workflow.TraceDrupal
+	(*TraceDrupalCacheEvent)(nil),    // 12: workflow.TraceDrupalCacheEvent
+	(*timestamppb.Timestamp)(nil),    // 13: google.protobuf.Timestamp
+	(*durationpb.Duration)(nil),      // 14: google.protobuf.Duration
 }
 var file_trace_proto_depIdxs = []int32{
-	2, // 0: workflow.StreamTracesResponse.Traces:type_name -> workflow.Trace
-	3, // 1: workflow.Trace.metadata:type_name -> workflow.TraceMetadata
-	4, // 2: workflow.Trace.function_calls:type_name -> workflow.TraceFunctionCall
-	5, // 3: workflow.TraceMetadata.start_time:type_name -> google.protobuf.Timestamp
-	5, // 4: workflow.TraceMetadata.end_time:type_name -> google.protobuf.Timestamp
-	5, // 5: workflow.TraceFunctionCall.start_time:type_name -> google.protobuf.Timestamp
-	6, // 6: workflow.TraceFunctionCall.elapsed:type_name -> google.protobuf.Duration
-	0, // 7: workflow.trace.StreamTraces:input_type -> workflow.StreamTracesRequest
-	1, // 8: workflow.trace.StreamTraces:output_type -> workflow.StreamTracesResponse
-	8, // [8:9] is the sub-list for method output_type
-	7, // [7:8] is the sub-list for method input_type
-	7, // [7:7] is the sub-list for extension type_name
-	7, // [7:7] is the sub-list for extension extendee
-	0, // [0:7] is the sub-list for field type_name
+	5,  // 0: workflow.StreamTracesResponse.Traces:type_name -> workflow.Trace
+	6,  // 1: workflow.Trace.metadata:type_name -> workflow.TraceMetadata
+	10, // 2: workflow.Trace.function_calls:type_name -> workflow.TraceFunctionCall
+	9,  // 3: workflow.Trace.resource_utilisation:type_name -> workflow.TraceResourceUtilisation
+	11, // 4: workflow.Trace.drupal:type_name -> workflow.TraceDrupal
+	13, // 5: workflow.TraceMetadata.start_time:type_name -> google.protobuf.Timestamp
+	13, // 6: workflow.TraceMetadata.end_time:type_name -> google.protobuf.Timestamp
+	0,  // 7: workflow.TraceMetadata.source:type_name -> workflow.TraceSource
+	1,  // 8: workflow.TraceMetadata.runtime:type_name -> workflow.TraceRuntime
+	7,  // 9: workflow.TraceMetadata.http:type_name -> workflow.TraceMetadataHTTP
+	8,  // 10: workflow.TraceMetadata.cli:type_name -> workflow.TraceMetadataCLI
+	14, // 11: workflow.TraceFunctionCall.offset:type_name -> google.protobuf.Duration
+	14, // 12: workflow.TraceFunctionCall.elapsed:type_name -> google.protobuf.Duration
+	12, // 13: workflow.TraceDrupal.cache_events:type_name -> workflow.TraceDrupalCacheEvent
+	2,  // 14: workflow.TraceDrupalCacheEvent.origin:type_name -> workflow.TraceDrupalCacheOrigin
+	14, // 15: workflow.TraceDrupalCacheEvent.offset:type_name -> google.protobuf.Duration
+	3,  // 16: workflow.trace.StreamTraces:input_type -> workflow.StreamTracesRequest
+	4,  // 17: workflow.trace.StreamTraces:output_type -> workflow.StreamTracesResponse
+	17, // [17:18] is the sub-list for method output_type
+	16, // [16:17] is the sub-list for method input_type
+	16, // [16:16] is the sub-list for extension type_name
+	16, // [16:16] is the sub-list for extension extendee
+	0,  // [0:16] is the sub-list for field type_name
 }
 
 func init() { file_trace_proto_init() }
@@ -475,6 +1093,42 @@ func file_trace_proto_init() {
 			}
 		}
 		file_trace_proto_msgTypes[4].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*TraceMetadataHTTP); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_trace_proto_msgTypes[5].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*TraceMetadataCLI); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_trace_proto_msgTypes[6].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*TraceResourceUtilisation); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_trace_proto_msgTypes[7].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*TraceFunctionCall); i {
 			case 0:
 				return &v.state
@@ -486,19 +1140,46 @@ func file_trace_proto_init() {
 				return nil
 			}
 		}
+		file_trace_proto_msgTypes[8].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*TraceDrupal); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_trace_proto_msgTypes[9].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*TraceDrupalCacheEvent); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
 	}
+	file_trace_proto_msgTypes[2].OneofWrappers = []interface{}{}
+	file_trace_proto_msgTypes[3].OneofWrappers = []interface{}{}
 	type x struct{}
 	out := protoimpl.TypeBuilder{
 		File: protoimpl.DescBuilder{
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_trace_proto_rawDesc,
-			NumEnums:      0,
-			NumMessages:   5,
+			NumEnums:      3,
+			NumMessages:   10,
 			NumExtensions: 0,
 			NumServices:   1,
 		},
 		GoTypes:           file_trace_proto_goTypes,
 		DependencyIndexes: file_trace_proto_depIdxs,
+		EnumInfos:         file_trace_proto_enumTypes,
 		MessageInfos:      file_trace_proto_msgTypes,
 	}.Build()
 	File_trace_proto = out.File
diff --git a/trace.proto b/trace.proto
index fb18057..b6ceaab 100644
--- a/trace.proto
+++ b/trace.proto
@@ -27,31 +27,114 @@ message StreamTracesResponse {
   repeated Trace Traces = 1; // List of traces.
 }
 
+// The invocation mechanism which produced the trace.
+enum TraceSource {
+  TRACE_SOURCE_UNSPECIFIED = 0;
+  TRACE_SOURCE_HTTP = 1; // Trace was collected from a HTTP request.
+  TRACE_SOURCE_CLI = 2;  // Trace was collected from the command line interface.
+}
+
+// The language runtime which produced the trace.
+enum TraceRuntime {
+  TRACE_RUNTIME_UNSPECIFIED = 0;
+  TRACE_RUNTIME_PHP = 1;  // Trace was collected from a PHP process.
+  TRACE_RUNTIME_NODE = 2; // Trace was collected from a Node.js process.
+}
+
 /**
  * Trace data provided by Compass.
  */
 message Trace {
-  TraceMetadata metadata = 1;                    // Metadata about the trace.
-  repeated TraceFunctionCall function_calls = 2; // List of function calls in the trace.
+  TraceMetadata metadata = 1;                              // Metadata about the trace.
+  repeated TraceFunctionCall function_calls = 2;           // List of function calls in the trace.
+  TraceResourceUtilisation resource_utilisation = 3;       // Resources consumed by the request.
+  optional TraceDrupal drupal = 4;                         // Drupal specific data. Only populated for PHP traces which called into the Drupal APIs.
 }
 
 /**
  * Metadata which contains information about the trace.
  */
 message TraceMetadata {
-  string request_id = 1;                     // Request identifier for tracking.
-  string uri = 2;                            // URI of the request being traced.
-  string method = 3;                         // HTTP method of the request (e.g., GET, POST).
-  google.protobuf.Timestamp start_time = 4;  // Start time of the trace in unix format.
-  google.protobuf.Timestamp end_time = 5;    // End time of the trace in unix format.
+  // Request identifier for tracking.
+  //
+  // Compass sends "UNKNOWN" when the request carried no HTTP_X_REQUEST_ID
+  // header. That is a sentinel, not an identifier: two traces reading UNKNOWN
+  // are not the same request, so anything correlating on this must treat it as
+  // absent.
+  string request_id = 1;
+  google.protobuf.Timestamp start_time = 2;  // Start time of the trace.
+  google.protobuf.Timestamp end_time = 3;    // End time of the trace.
+  TraceSource source = 4;                    // How the traced request was invoked.
+  TraceRuntime runtime = 5;                  // Language runtime which produced the trace.
+  optional TraceMetadataHTTP http = 6;       // Request details. Only set when source is TRACE_SOURCE_HTTP.
+  optional TraceMetadataCLI cli = 7;         // Command details. Only set when source is TRACE_SOURCE_CLI.
+}
+
+/**
+ * Metadata for a trace which was invoked by a HTTP request.
+ */
+message TraceMetadataHTTP {
+  string method = 1; // HTTP method of the request (e.g., GET, POST).
+  string uri = 2;    // URI of the request being traced.
+}
+
+/**
+ * Metadata for a trace which was invoked from the command line.
+ */
+message TraceMetadataCLI {
+  string command = 1; // Command which was executed.
+}
+
+/**
+ * Resources consumed over the course of the traced request.
+ */
+message TraceResourceUtilisation {
+  int64 max_memory = 1; // Peak memory used by the request, in bytes.
 }
 
 /**
  * Function call data within a trace.
  */
 message TraceFunctionCall {
-  string name = 1;                           // Name of the function being traced.
-  google.protobuf.Timestamp start_time = 2;  // Start time of the function call in unix format.
-  google.protobuf.Duration elapsed = 3;      // Elapsed time for the function call in milliseconds.
+  string name = 1;                        // Name of the function being traced.
+  google.protobuf.Duration offset = 2;    // Offset from the start of the request at which the call began.
+  google.protobuf.Duration elapsed = 3;   // How long the call ran for.
+  int64 memory = 4;                       // Memory used by the call, in bytes.
+}
+
+// Which Drupal API produced a cache event.
+enum TraceDrupalCacheOrigin {
+  TRACE_DRUPAL_CACHE_ORIGIN_UNSPECIFIED = 0;
+  TRACE_DRUPAL_CACHE_ORIGIN_RENDER_ARRAY = 1; // Cacheability was collected from a render array.
+  TRACE_DRUPAL_CACHE_ORIGIN_OBJECT = 2;       // Cacheability was collected from an object.
+}
+
+/**
+ * Drupal specific data collected for a trace.
+ *
+ * Only populated for PHP traces where the application called into the Drupal
+ * APIs which Compass probes, so it is absent for Node traces, PHP CLI traces
+ * and non-Drupal PHP applications.
+ */
+message TraceDrupal {
+  repeated TraceDrupalCacheEvent cache_events = 1; // Cache events which occurred during this trace, aggregated by their contents.
+  int64 cache_events_dropped = 2;                  // How many distinct cache events were discarded because the trace reached its retention limit. Reported so that a truncated trace is not mistaken for a complete one.
 }
 
+/**
+ * Cacheability metadata that Drupal derived at a point in the request.
+ *
+ * Drupal derives cacheability far more often than a request has interesting
+ * function calls, so identical events are aggregated into a single entry with a
+ * call count rather than retained individually.
+ */
+message TraceDrupalCacheEvent {
+  TraceDrupalCacheOrigin origin = 1;   // Origin of the cacheability metadata.
+  string caller = 2;                   // Caller which asked Drupal for the cacheability metadata.
+  string object_type = 3;              // Type the metadata was derived from. Only set for TRACE_DRUPAL_CACHE_ORIGIN_OBJECT.
+  int64 max_age = 4;                   // Max age in seconds, where -1 means cacheable forever.
+  repeated string tags = 5;            // Tags which the cached item is invalidated by.
+  repeated string contexts = 6;        // Contexts which the cached item varies by.
+  google.protobuf.Duration offset = 7; // Offset from the start of the request at which the first of these events occurred.
+  int64 calls = 8;                     // How many identical events were aggregated into this one.
+}