Function default_stt_engine 

pub fn default_stt_engine() -> String

The cross-surface default STT engine, resolved as a swappable default (never a hardcoded literal). Parakeet v3 (in-process ONNX) is the default whenever this build compiled the voice-parakeet feature. Lean builds omit the feature and default to whisper.cpp so transcription still works there. RYU_STT_ENGINE overrides both, so one env var re-points every surface.

Which builds carry the feature is a release-pipeline fact, and it has been wrong before: the flag lived only in apps/core/package.json (dev/ dev:watch/build), so every developer had parakeet while the three binaries users actually install — .github/workflows/release.yml, scripts/release/release-local.sh, Dockerfile — were built featureless and silently defaulted to whisper. All four sites now pass --features sandbox-wasmtime,voice-parakeet,voice-vad; keep them in sync (the release workflow asserts the resolved feature graph).