test(cli): cover prerouter defaults at engine dispatch

[agourakis82]

What & why

Add CLI dispatch coverage for the intentional prerouter defaults. The registry helper is already tested, but these cases also check the arguments that actually reach AutoEngine.from_pretrained through demo, chat, and serve.

The 12 cases cover both model tiers with and without --no-prerouter. Only the 8B demo disables the prerouter by default; chat, serve, and the 35B demo preserve their normal defaults. No runtime behavior changes.

Area

• Python framework (python/)

How was it tested?

On Apple Silicon/macOS, from python/:

python -m pytest -q -rs tests/test_cli_flags.py tests/test_registry.py tests/test_server.py tests/test_tool_calls.py tests/test_repo_hygiene.py

106 passed, no skips, with Flask installed in the local test environment. Dependency pins are unchanged.

A process-local negative control replaced demo_kwargs with a passthrough: the new default 8B demo case failed as expected, while the other 11 new cases passed. No source mutation was retained.

The new tests stop at a mocked engine constructor. They do not load weights or validate numerical inference. The complete pytest -m 'not slow' suite was not run locally; the command above is the full extent of this candidate's local test validation.

Checklist

• pytest -m 'not slow' passes locally (full suite not run)
• Repo hygiene passes
• Added regression coverage for existing behavior
• Dependency pins unchanged
• No user-facing behavior or documentation changes needed

AI assistance was used for implementation and review, including a local Edge0/MLX review. The changes and test results were checked before submission.

[shuk777]

LGTM, thanks for the pr!