vt::Conv2d has no CUDA provider, so the shared 2-D convolution seam cannot run on a GPU

Row: KERNEL-VT-CONV2D-CUDA

vt::Conv2d (include/vt/ops.h:4428) has exactly ONE provider in the tree:

$ grep -rn "OpId::kConv2d" src/ include/
src/vt/op_provider.cpp:566:    case OpId::kConv2d:
src/vt/ops.cpp:3282:  reinterpret_cast<Conv2dFn>(GetOp(OpId::kConv2d, q.device.type))(q, out, x, weight, bias, args);
src/vt/cpu/cpu_conv2d.cpp:111:    RegisterOp(OpId::kConv2d, DeviceType::kCPU,

src/vt/cpu/cpu_conv2d.cpp:111 is the CPU registration and there is no CUDA
one, so vt::Conv2d on a CUDA queue resolves no op. Any model that routes a
2-D convolution through the shared seam therefore ships a capability that
cannot run on the only device class that could serve it.

Why this is being filed now

dots3-note W7a (#2703) ports the dots speech encoder, whose stem is three
Conv2d(kernel=3, stride=2) layers (nvidia/audio_encoder.py:466-474 @
9035151d6). It composes them as host im2col + vt::MatmulBT and records ONE
EXACT TRACKED EXCEPTION to the kConv2d seam, with this issue as the reason.
The in-tree precedent is include/vllm/model_executor/models/whisper_audio.h:33,
which composes its Conv1d stem the same way and says "no new CUDA kernel".

The exception is the right call for that slice — a stem routed through
kConv2d would fault on the queue every real deployment uses — but the gap
outlives it. It is a vt gap, not a model gap.

What closing it looks like

A CUDA provider for OpId::kConv2d matching the CPU one's contract
(src/vt/cpu/cpu_conv2d.cpp), gated the way the other CUDA op ports are: a
red-first CPU/CUDA agreement test over the shapes the registered callers use,
plus the arch gate check-cuda-op-arch-gate already applies. Then each im2col
composition that exists only because of this gap can be reconsidered on a
measurement rather than on availability.

Not in scope here

vt::Conv3d (ops.h:4475) and vt::Conv1d (ops.h:4609) have their own
provider tables and are not measured by this issue.

Start with include/vt/ops.h:4428, src/vt/cpu/cpu_conv2d.cpp:111, and the dispatch in src/vt/ops.cpp:3282 to understand the Conv2d contract and provider registration. Run the existing check-cuda-op-arch-gate and inspect the red-first CPU/CUDA agreement coverage for registered caller shapes. Done means a CUDA OpId::kConv2d provider is registered, passes the agreement test, and satisfies the architecture gate.