Parakeet transcription randomly truncates before end of recording

[poodle64]

Description

When using the Parakeet (Sherpa-ONNX) backend via Apple Neural Engine, transcription sometimes cuts off before the end of the recording. The truncation point appears random; no clear user action differentiates successful from truncated transcriptions.

Steps to Reproduce

1. Record audio using any recording mode
2. Speak for 10-30 seconds
3. Stop recording
4. Observe transcription output

Expected: Full transcription of entire recording
Actual: Sometimes truncates mid-sentence, sometimes works perfectly

Investigation Notes

• No obvious correlation with recording length, audio level, or content
• May be related to audio buffer handling or decoder state in Sherpa-ONNX
• Could be a timing issue between audio capture stop and transcription start
• Check if the WAV file written to disk contains the full audio vs what the decoder receives

Relevant Files

• src-tauri/src/transcription/parakeet.rs
• src-tauri/src/audio/mod.rs (buffer handling at stop)
• src-tauri/src/pipeline.rs (recording stop → transcription handoff)