feat(transcription): carry speaker labels on words and streamed segments

A diarizing backend could label transcript segments, but two paths
dropped the label: TranscriptWord had no speaker field, so live
transcription words and word-level timestamps could not carry one, and
the stream=true transcript.text.done event left the speaker out of
its segments.

TranscriptWord gains an optional speaker (proto field 4, additive).
It flows through the live event and result mapping, the JSON word
output of the endpoint and the CLI, and transcript.text.done now
includes a segment's speaker when there is one. Empty labels are
omitted, so responses without diarization are unchanged.

Assisted-by: Claude:claude-opus-5-5 [Claude Code]

backend/backend.proto

@@ -647,6 +647,7 @@ message TranscriptWord {
   int64 start = 1;
   int64 end = 2;
   string text = 3;
+  string speaker = 4;   // backend speaker label when diarizing; empty otherwise
 }
 
 message TranscriptSegment {

core/backend/transcript.go

@@ -213,9 +213,10 @@ func transcriptResultFromProto(r *proto.TranscriptResult) *schema.TranscriptionR
 		var words []schema.TranscriptionWord
 		for _, w := range s.Words {
 			var word = schema.TranscriptionWord{
-				Start: time.Duration(w.Start),
-				End:   time.Duration(w.End),
-				Text:  w.Text,
+				Start:   time.Duration(w.Start),
+				End:     time.Duration(w.End),
+				Text:    w.Text,
+				Speaker: w.Speaker,
 			}
 			words = append(words, word)
 			tr.Words = append(tr.Words, word)

core/backend/transcript_live.go

@@ -298,9 +298,10 @@ func liveEventFromProto(r *proto.TranscriptLiveResponse) LiveTranscriptionEvent
 	}
 	for _, w := range r.GetWords() {
 		ev.Words = append(ev.Words, schema.TranscriptionWord{
-			Start: time.Duration(w.Start),
-			End:   time.Duration(w.End),
-			Text:  w.Text,
+			Start:   time.Duration(w.Start),
+			End:     time.Duration(w.End),
+			Text:    w.Text,
+			Speaker: w.Speaker,
 		})
 	}
 	if r.GetFinalResult() != nil {

core/backend/transcript_live_internal_test.go

@@ -54,6 +54,20 @@ var _ = Describe("liveEventFromProto", func() {
 		Expect(ev.Final).To(BeNil())
 	})
 
+	It("carries word speakers and final segment speakers from a diarizing backend", func() {
+		ev := liveEventFromProto(&proto.TranscriptLiveResponse{
+			Words: []*proto.TranscriptWord{{Text: "hi", Speaker: "1"}},
+		})
+		Expect(ev.Words[0].Speaker).To(Equal("1"))
+		ev = liveEventFromProto(&proto.TranscriptLiveResponse{
+			FinalResult: &proto.TranscriptResult{
+				Text:     "hi there",
+				Segments: []*proto.TranscriptSegment{{Text: "hi", Speaker: "0"}, {Text: "there", Speaker: "1"}},
+			},
+		})
+		Expect(ev.Final.Segments[1].Speaker).To(Equal("1"))
+	})
+
 	It("maps the eob backchannel flag separately from eou", func() {
 		ev := liveEventFromProto(&proto.TranscriptLiveResponse{Delta: "uh-huh", Eob: true})
 		Expect(ev.Eob).To(BeTrue())

core/cli/transcript.go

@@ -93,18 +93,20 @@ func (t *TranscriptCMD) Run(ctx *cliContext.Context) error {
 		}
 		for _, word := range(tr.Words) {
 			trs.Words = append(trs.Words, schema.TranscriptionWordSeconds{
-				Start: word.Start.Seconds(),
-				End:   word.End.Seconds(),
-				Text:  word.Text,
+				Start:   word.Start.Seconds(),
+				End:     word.End.Seconds(),
+				Text:    word.Text,
+				Speaker: word.Speaker,
 			})
 		}
 		for _, seg := range(tr.Segments) {
 			segWords := []schema.TranscriptionWordSeconds{}
 			for _, word := range(seg.Words) {
 				segWords = append(segWords, schema.TranscriptionWordSeconds{
-					Start: word.Start.Seconds(),
-					End:   word.End.Seconds(),
-					Text:  word.Text,
+					Start:   word.Start.Seconds(),
+					End:     word.End.Seconds(),
+					Text:    word.Text,
+					Speaker: word.Speaker,
 				})
 			}
 			trs.Segments = append(trs.Segments, schema.TranscriptionSegmentSeconds{

core/http/endpoints/openai/transcription.go

@@ -191,18 +191,20 @@ func TranscriptEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, app
 			}
 			for _, word := range tr.Words {
 				trs.Words = append(trs.Words, schema.TranscriptionWordSeconds{
-					Start: word.Start.Seconds(),
-					End:   word.End.Seconds(),
-					Text:  word.Text,
+					Start:   word.Start.Seconds(),
+					End:     word.End.Seconds(),
+					Text:    word.Text,
+					Speaker: word.Speaker,
 				})
 			}
 			for _, seg := range tr.Segments {
 				segWords := []schema.TranscriptionWordSeconds{}
 				for _, word := range seg.Words {
 					segWords = append(segWords, schema.TranscriptionWordSeconds{
-						Start: word.Start.Seconds(),
-						End:   word.End.Seconds(),
-						Text:  word.Text,
+						Start:   word.Start.Seconds(),
+						End:     word.End.Seconds(),
+						Text:    word.Text,
+						Speaker: word.Speaker,
 					})
 				}
 				trs.Segments = append(trs.Segments, schema.TranscriptionSegmentSeconds{
@@ -309,12 +311,16 @@ func streamTranscription(c echo.Context, req backend.TranscriptionRequest, ml *m
 	if len(finalResult.Segments) > 0 {
 		segs := make([]map[string]any, 0, len(finalResult.Segments))
 		for _, seg := range finalResult.Segments {
-			segs = append(segs, map[string]any{
+			entry := map[string]any{
 				"id":    seg.Id,
 				"start": seg.Start.Seconds(),
 				"end":   seg.End.Seconds(),
 				"text":  seg.Text,
-			})
+			}
+			if seg.Speaker != "" {
+				entry["speaker"] = seg.Speaker
+			}
+			segs = append(segs, entry)
 		}
 		doneEvent["segments"] = segs
 	}

core/schema/transcription.go

@@ -13,9 +13,10 @@ type TranscriptionSegment struct {
 }
 
 type TranscriptionWord struct {
-	Start time.Duration `json:"start"`
-	End   time.Duration `json:"end"`
-	Text  string        `json:"text"`
+	Start   time.Duration `json:"start"`
+	End     time.Duration `json:"end"`
+	Text    string        `json:"text"`
+	Speaker string        `json:"speaker,omitempty"`
 }
 
 type TranscriptionResult struct {
@@ -42,9 +43,10 @@ type TranscriptionSegmentSeconds struct {
 }
 
 type TranscriptionWordSeconds struct {
-	Start float64 `json:"start"`
-	End   float64 `json:"end"`
-	Text  string  `json:"text"`
+	Start   float64 `json:"start"`
+	End     float64 `json:"end"`
+	Text    string  `json:"text"`
+	Speaker string  `json:"speaker,omitempty"`
 }
 
 type TranscriptionResultSeconds struct {