Refs #1931.
torchaudio 2.9 removed set_audio_backend(). soundfile has been the only backend
since 2.0, so the call was already a no-op — but unguarded it raises
AttributeError inside the ml_imports startup phase, and a failure there takes
the whole backend down: the desktop app sits on "starting backend" forever and
/health stays 503.
The group hitting it is not hypothetical. RTX 50-series (Blackwell, sm_120)
cards have no kernels in the pinned torch 2.8.0, so those users MUST move to
torch 2.9.x, which brings torchaudio 2.9 with it. Being forced to upgrade and
then crashing on a line that does nothing is the whole defect.
This does NOT raise the torch pin. Doing that changes the CUDA build on every
platform, in Docker and in CI, so it is the owner's call rather than something
to slip into a bug fix — the issue stays open for it. What lands here is the
half that is safe: the guard, plus a troubleshooting section with the exact
upgrade recipe and the command to confirm the card is visible, so an affected
user has a supported path today.
The guard is tested at the source level: reproducing it needs a real torchaudio
2.9 in the environment, which the pinned test env does not have. One test also
pins that the guard actually WRAPS the call, since a hasattr elsewhere in the
file would satisfy a naive substring check while the real call stayed bare.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017ypcgSsh5j2PEonSJiAU1S
