stop_recording now, when the mic is on, takes 'You' spans straight from the MicActivity timeline and diarizes the recording with those ranges zeroed, so sherpa only ever clusters the far side into Speaker N. Merges the span lists and names them via the existing voiceprint map (You + Speaker 2..). Falls back to the whole-signal pass + voiceprint match when the mic is off. Adds mask_ranges helper + tests.