700/700 params, max abs diff 1.2e-5 on the real 1.3B checkpoint.
Key realisation: the flow models have no sparse conv, so upstream RUNS on CPU torch
with flash-attn swapped for SDPA. That gives a real numerical oracle - unavailable for
the sparse path, where spconv cannot be installed at all.
It was needed. Three bugs survived a loader reporting a perfect 700/700 with zero
missing and zero unmapped keys:
- a parameterless final LayerNorm (no params -> no checkpoint trace) that the output
was 200x too large without
- rope_phases being complex64, so the rotation is a complex multiply
- qk_rms_norm belonging before rope rather than after
Weight-key matching is necessary but nowhere near sufficient for a port.
