set_model_compute_dtype sets force_cast_weights on purpose: it is what
casts each layer's weights to match. Clearing it afterwards left the model
casting its INPUT to the chosen dtype while the weights stayed as loaded,
so the first Linear of the first sampling step raised "mat1 and mat2 must
have the same dtype".
Picking any compute dtype other than default therefore broke sampling on a
full-VRAM load. It survives on constrained hardware only because the
low-VRAM path forces the cast back on by itself, which is why nobody hit it.
Straight port from v4, where the same line has shipped since 3837f8f. The
branch had no test at all; it now has one that fails against the old line.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
