The Cookbook's manual hardware simulator ("what if I had this setup") let users
pick a backend, but _apply_manual_hardware only accepted cuda/rocm/cpu_x86/
cpu_arm and silently coerced anything else to cuda. So selecting Apple/Metal
simulated a CUDA box instead — and ranked safetensors-only repos a Mac can't
serve, even though the rest of hwfit (services.hwfit.fit, the serve-command
generation) already supports Metal as GGUF-only via llama.cpp/Ollama.
Add "metal" to the accepted backends (now a named _MANUAL_BACKENDS set, kept a
subset of what fit.py understands) and set unified_memory=True for it — Apple
Silicon shares one memory pool with the GPU — while clearing that flag for the
discrete (cuda/rocm) and CPU backends. _apply_manual_hardware is lifted to
module scope so it is directly unit-testable; both route call sites are
unchanged.
Adds tests/test_hwfit_manual_backend.py, including an end-to-end check that a
simulated Metal box only recommends GGUF-servable models.
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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