feat(diarization): live tick re-emits relabeled segments + live 'You' (FR-SPK)

Phase 2 backend. The 15s provisional pass now (1) runs the mic voiceprint
match every tick and merges 'You'/'Speaker N' into the session name map without
overwriting user-set names, and (2) re-emits every committed segment whose
speaker changed via transcript://segment (replace-by-id) so the live transcript
reflects the refined labels instead of a frozen 'S1'.

src-tauri/src/commands.rs

@@ -512,6 +512,7 @@ pub async fn start_recording(
         let wav_path_for_diar = wav_path.clone();
         let segments_for_diar = segments.clone();
         let names_for_diar = speaker_names.clone();
+        let voice_sample_for_diar = mic_voice_sample.clone();
         tauri::async_runtime::spawn(async move {
             // ponytail: reprocesses the whole recording-so-far each tick
             // rather than incremental/windowed segmentation — sherpa-onnx's
@@ -552,16 +553,59 @@ pub async fn start_recording(
                     }
                 };
 
-                let speakers = {
+                let (speakers, changed) = {
                     let mut segs = segments_for_diar.lock().unwrap_or_else(|e| e.into_inner());
+                    // Snapshot prior labels so only segments whose speaker
+                    // actually changed this pass get re-emitted (ids are stable;
+                    // the frontend replaces by id).
+                    let before: HashMap<u64, String> =
+                        segs.iter().map(|s| (s.id, s.speaker.clone())).collect();
                     diarizer.assign(&mut segs, &spans);
+
+                    // Live "You": match the mic voiceprint against this pass's
+                    // clusters. Clusters re-shuffle every tick so match every
+                    // tick; never overwrite a name already set (user rename or a
+                    // prior pass) — same guard as the post-stop pass.
+                    if let Some(voice_sample) = &voice_sample_for_diar {
+                        let mic_samples = voice_sample.samples();
+                        match crate::diarization::voiceprint::match_mic_speaker(
+                            &diarization_embedding_model_file(),
+                            &mic_samples,
+                            &wav_path_for_diar,
+                            &spans,
+                        ) {
+                            Ok(auto_names) => {
+                                let mut names =
+                                    names_for_diar.lock().unwrap_or_else(|e| e.into_inner());
+                                for (label, name) in auto_names {
+                                    names.entry(label).or_insert(name);
+                                }
+                            }
+                            Err(e) => tracing::warn!("live voiceprint match failed: {e}"),
+                        }
+                    }
+
                     let names = names_for_diar.lock().unwrap_or_else(|e| e.into_inner());
-                    speaker_infos_from_segments(&segs, &names)
+                    let changed: Vec<TranscriptSegment> = segs
+                        .iter()
+                        .filter(|s| before.get(&s.id) != Some(&s.speaker))
+                        .cloned()
+                        .collect();
+                    (speaker_infos_from_segments(&segs, &names), changed)
                 };
                 let _ = app_for_diar.emit(
                     "diarization://updated",
                     serde_json::json!({ "meetingId": meeting_id_for_diar, "speakers": speakers }),
                 );
+                // Re-emit relabeled committed segments so the live transcript
+                // reflects the refined speakers without a new event type
+                // (docs/04-api-contracts.md: transcript://segment is replace-by-id).
+                for segment in &changed {
+                    let _ = app_for_diar.emit(
+                        "transcript://segment",
+                        serde_json::json!({ "meetingId": meeting_id_for_diar, "segment": segment }),
+                    );
+                }
             }
         });
     }