Function denoise_pcm_24k 

pub fn denoise_pcm_24k(
    bundle: &ModelBundle,
    pcm: &[f32],
) -> Result<Option<Vec<f32>>, FttsError>

Denoise arbitrary mono 24 kHz PCM through the pulled neural denoiser, if present.

Ok(None) when the neural route is unavailable — the caller keeps the original. Split out for hosts (the iOS app through ftts-ffi) that clean synthesized OUTPUT; enrollment keeps its own opt-in path through ReferenceCleanup.

Errors

When the artifact is present but unreadable — a broken denoiser is repaired, not silently swapped for a different one.