tests: make the MLX boundary guard catch mlx_lm imports

[VKVstudio]

What

tests/test_repo_hygiene.py::test_mlx_imports_stay_inside_the_backend enforces the rule stated in backends/__init__.py: MLX packages are imported only under edge0/backends/mlx/. Its regex requires a space or a dot right after mlx, so from mlx_lm.models... import ... never matches and the guard silently passes framework code that imports mlx_lm directly.

This PR tightens the pattern to ^\s*(?:from|import)\s+mlx(?:_lm)?\b.

What it finds

The stricter guard immediately flags src/edge0/streaming/layer.py:49:

from mlx_lm.models.switch_layers import _gather_sort, _scatter_unsort

Rather than turn CI red on an existing file, that path is listed in an explicit _MLX_IMPORT_KNOWN_VIOLATIONS set with a note on what should move into the framework. Remove the entry once the two helpers no longer come from mlx_lm. I'm happy to send that follow-up: they are a few lines of argsort/gather that can live next to moe/routing.py, which would also make the streaming layer importable on a non-MLX backend.

If you would rather have the guard fail loudly instead, drop the allowlist — the regex change alone is the fix.

Checks

• pytest tests/test_repo_hygiene.py — 4 passed. The file imports nothing from edge0 or mlx, so this runs on any platform, same as the existing Linux hygiene job.
• The tightened regex matches import mlx, import mlx.core as mx, from mlx_lm import x, from mlx_lm.models.base import ..., and does not match from edge0.backends.mlx._impl import ... or a hypothetical mlxfoo package.

Context

I'm working on a CUDA/PyTorch backend for the reserved backends/cuda/ slot (https://github.com/smartbulldog-pro/edge0-cuda/tree/cuda-backend). This import is the one thing that keeps streaming/layer.py from importing on a non-MLX backend, which is how I ran into the guard.

[shuk777]

Thanks for catching this gap. The check should cover mlx_lm as well as mlx. Recording the existing streaming-layer import in an allowlist keeps CI green, and the change is worth taking.

The conflict is from the test file moving. Please don't restore tests/test_repo_hygiene.py at the repo root. Apply it on python/tests/test_repo_hygiene.py instead:

• Use the regex ^\s*(?:from|import)\s+mlx(?:_lm)?\b
• Put python/src/edge0/streaming/layer.py in the allowlist
• Keep the scan on python/src/edge0, and skip allowlisted files

Moving _gather_sort and _scatter_unsort out of mlx_lm would change the streaming path, and it is not required for this PR. Our next step is a unified inference framework across all platforms, planned for November. It is a substantial rework of the current framework, so there is no need to do that move on the current tree. We will use your notes as a reference. Once the new framework is out, we will let you know right away.

Thanks again.

[VKVstudio]

Thanks for the review. Updated as requested:

• Merged current main into the branch; the guard now lives at python/tests/test_repo_hygiene.py (root file not restored).
• Regex is ^\s*(?:from|import)\s+mlx(?:_lm)?\b in a raw string. The previous commit contained a stray backspace byte instead of \b, which made the pattern match nothing; that is fixed too.
• python/src/edge0/streaming/layer.py is in the allowlist, and the scan stays on python/src/edge0.
• pytest python/tests/test_repo_hygiene.py: 6 passed.

I will not send the _gather_sort / _scatter_unsort follow-up. Glad the notes are useful, and I look forward to the unified framework in November.

[VKVstudio]

Force-pushed to fix the commit author; the branch is now a single commit on top of current main, with the same content as before.

[shuk777]

LGTM, thanks for ur contribute!