Previously, progress messages were only sent every 5th segment due to
a `segment_count % 5` guard. This made the UI feel unresponsive for
short recordings with few segments. Now every segment emits a progress
update with a more descriptive message including the segment number
and audio percentage.
Adds a test verifying that all 8 mock segments produce progress
messages, not just every 5th.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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