An all-grouped container (kv_b_proj at fmt=4) generates one correct token
and then EOS: qt_addrow and qt_matvec_rows handle fmt 0/1/2 and fall
through to the int2 decoder, so grouped-int4 kv_b was unpacked as 2-bit
pairs under a per-row scale that does not exist in the [O,ng] layout.
Prefill (S>4, reconstruction) is unaffected, which made the failure look
like an EOS bug rather than an attention bug.
Same class as #298 (CUDA absorb kernels missing fmt=4), CPU side. Existing
containers escape it because the recommended mixed-precision recipe keeps
kv_b at int8 (#237).
Adds per-group branches mirroring matmul_i4_grouped semantics. fmt 0/1/2/3
paths are untouched.
Co-Authored-By: Claude <noreply@anthropic.com>
bokiko
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