fix: winml config --device npu silently succeeds when no NPU EP is available

[DingmaomaoBJTU]

Summary

When --device npu is specified but no NPU execution provider (VitisAI, QNN) is available, winml config emits a WARNING but still exits 0 and writes a config with \"execution_provider\": \"qnn\" — guaranteeing a failure at compile/inference time.

Context

There are two independent device-availability checks that can disagree:

1. Hardware detection (_get_available_devices()): WMI-based, detects NPU silicon → adds \"npu\" to available_devices
2. EP detection (_get_available_eps()): ORT/WinML provider enumeration → may not find QNNExecutionProvider or VitisAIExecutionProvider (e.g. QNN SDK not installed, wrong ORT build)

When these disagree, the tool currently warns and proceeds — creating a config that will fail downstream.

Repro

On a machine with NPU hardware but no QNN/VitisAI EP (e.g. standard pip install onnxruntime, no QNN SDK):

winml config -m microsoft/resnet-50 --device npu --precision int8 -o out.json

Observed:

WARNING - Device 'npu' requested but no compatible EP found.
  Compatible EPs: ['VitisAIExecutionProvider', 'QNNExecutionProvider'].
  Available EPs:  ['CPUExecutionProvider', 'DmlExecutionProvider',
                   'NvTensorRTRTXExecutionProvider', 'OpenVINOExecutionProvider'].
INFO  - Device resolved: npu (available: npu, gpu, cpu)
✅ Config saved to: out.json          ← exits 0

out.json contains \"execution_provider\": \"qnn\" — an EP that was just flagged as unavailable.

Expected: Either an error exit (EP not available → config would be unusable), or at minimum a visible mismatch between the "no compatible EP" warning and the "Device resolved: npu" success message.

Current State

• src/winml/modelkit/sysinfo/device.py:183–191 — resolve_device() warns but unconditionally returns (device, available_devices) for explicit device requests
• src/winml/modelkit/sysinfo/device.py:77–109 — _get_available_devices() is hardware-only (WMI); does not consult EP availability
• src/winml/modelkit/config/build.py:279–284 and :573–578 — callers log "Device resolved" using available_devices from hardware detection, contradicting the EP-level warning

Desired State

When an explicit --device <X> is requested but no compatible EP is available, one of:

• Option A (stricter): resolve_device() raises an error — the user asked for a device that cannot work. The CLI should print a clear error and exit non-zero.
• Option B (softer): EP availability gates available_devices — if no NPU EP is found, "npu" is not reported as available, and --device npu triggers a clear "device unavailable" error.

Option A is simpler and more actionable for users.

Acceptance Criteria

• winml config --device npu exits non-zero with a clear error message when no NPU EP (VitisAI, QNN) is available in the current environment
• The error message names the missing compatible EPs so the user knows what to install
• --device auto is unaffected: if no NPU EP is available, auto silently falls through to GPU/CPU (existing behavior is correct)
• uv run pytest tests/ passes

Technical Notes

• The fix is localized to resolve_device() in src/winml/modelkit/sysinfo/device.py:181–191. For explicit devices (non-auto), a missing compatible EP should raise ValueError rather than log a warning.
• _get_available_devices() (hardware detection) and _get_available_eps() (EP detection) deliberately use different mechanisms — this is intentional for the auto path. The fix should not merge them; it should just make the explicit-device path harder on the mismatch.
• The two call sites in build.py (lines 279, 573) don't need changes if the error is raised inside resolve_device().
• CLAUDE.md naming convention: EP acronyms are uppercase (QNN, NPU, GPU, CPU).

Related Files

• src/winml/modelkit/sysinfo/device.py:146–191 — resolve_device(), the fix site
• src/winml/modelkit/sysinfo/device.py:77–109 — _get_available_devices() (hardware)
• src/winml/modelkit/sysinfo/device.py:112–143 — _get_available_eps() (ORT/WinML)
• src/winml/modelkit/config/build.py:279–284 — first caller of resolve_device()
• src/winml/modelkit/config/build.py:573–578 — second caller of resolve_device()
• tests/sysinfo/ — add test: mock _get_available_eps() to return only CPU EP, call resolve_device("npu"), assert ValueError

[DingmaomaoBJTU]

Triage summary

• Component: Sys
• Priority: P1
• Owner(s): @chinazhangchao

winml config --device npu silently exits 0 and writes an unusable config when no compatible NPU EP is available; resolve_device() should raise an error for explicit device requests with no matching EP.