QMoE: fail loudly when weights_prepacked=0 but PrePack did not run (#28965)
### Description
When a QMoE model sets `weights_prepacked=0` (raw `[E, N, K/pack]` int
weights) and the session has `session.disable_prepacking`, `PrePack()`
never runs, so `packed_fc{1,2}_weights_` stay null and
`int_weights_consumed_by_prepack` is false. The code then falls through
to the raw initializer pointers — but those bytes are not in CUTLASS
layout, so the runner consumes them as-if-prepacked and produces
silently wrong output with no diagnostic.
Changes in `onnxruntime/contrib_ops/cuda/moe/moe_quantization.cc`
(`QMoE::ComputeInternal`):
- **Int path**: Added a defensive `INVALID_ARGUMENT` guard — when
`is_int && !weights_prepacked_` but either prepack buffer is null,
return a clear error instead of feeding non-CUTLASS bytes to the runner.
- **wfp4afp8 native path**: Same fall-through
(`packed_fp4_fc{1,2}_weights_ ? ... : raw`) replaced with an explicit
guard that errors when the repacked FP4 buffers were not produced.
Also added a focused regression test in
`onnxruntime/test/contrib_ops/moe_test.cc` covering `quant_type='int'`
with `weights_prepacked=0` and `session.disable_prepacking=1`, asserting
that QMoE fails with an actionable error instead of producing output.
Merged the branch with the latest `main`.
### Motivation and Context
A prior fix removed the null-pointer crash on this path but left a
misleading-success outcome that is newly user-reachable via the
`weights_prepacked=0` contract — the exact silent-failure mode the
offline-path work set out to eliminate. These guards convert that into a
loud, actionable error. The wfp4afp8 branch shares the same fall-through
and is hardened for consistency.
The added regression test ensures this fail-loudly behavior remains
covered going forward, especially when prepacking is disabled at the
session level.
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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
onnxruntime
cf509d84 - QMoE: fail loudly when weights_prepacked=0 but PrePack did not run (#28965)
