When sageattn fails, q/k/v are already in [b,n,s,d] format from the
rearrange before the call. Use SDPA directly on them instead of calling
_sdpa_fallback which expects [b,s,(n*d)] and crashes with a shape error.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
SageAttention CUDA kernels don't support Blackwell yet. Catch runtime
failures from sageattn/sparse_sageattn, disable them, and fall back to
PyTorch SDPA. Only pays the try/except cost once per session.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Verify attention backend functions are actually callable before marking
them available. Falls back to PyTorch SDPA instead of calling None.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Vendor minimal diffsynth subset for FlashVSR inference (full/tiny pipelines,
v1 and v1.1 checkpoints auto-downloaded from HuggingFace). Includes segment-based
processing with temporal overlap and crossfade blending for bounded RAM on long videos.
Nodes: Load FlashVSR Model, FlashVSR Upscale, FlashVSR Segment Upscale.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
