File "codai/api/video.py", line 4176, in _generate_longcat
      payload["audio"] = _as_b64(_audio)
    NameError: name '_as_b64' is not defined

_as_b64 was defined INSIDE _generate_h3, MiniMax H3's handler, and
_generate_longcat referenced it across that scope. So every LongCat path that
carries binary input raised NameError before reaching the worker: the avatar
audio track (at2v), the reference image (ai2v and i2v), and continuation frames.
Text-to-video is the only path that never touches it, which is why t2v was the
only one that ever worked.

It cost a 20-minute wait for the GPU to find out, because the NameError fires
after the model is loaded and the swap gate has handed over.

Now module level, beside the _decode_b64_or_url it wraps. The test walks the AST
for a call site in a function that neither defines it nor is nested in one that
does, so the same mistake in another backend fails here instead of on a rented
GPU.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0185zEBiy3KWB37xNGSrxL7w