Simulation silently no-ops on macOS — platform.system() returns "Darwin", not "OSX"

[Tessenderman]

File: pygarment/meshgen/simulation.py, function _run_frame_with_timeout

Bug

elif platform.system() in ["Linux", "OSX"]:

platform.system() returns "Darwin" on macOS, never "OSX". Since the
if platform.system() == "Windows" branch above it also doesn't match,
neither branch executes on macOS — garment.run_frame() is never
called, for any frame, for the entire simulation.

Impact

This fails silently. sim_frame_sequence's loop still runs its full
max_sim_steps, prints progress normally, and exits with no error — but
the cloth mesh is never actually updated. The "simulated" output is
pixel-for-pixel (vertex-for-vertex) identical to the pre-simulation box
mesh.

Confirmed by diffing *_sim.obj against *_boxmesh.obj for the same
element: mean per-vertex displacement ~2.4e-6 (floating-point noise, not
physics), max ~7.6e-6. Reproduces identically on your own shipped example
patterns (e.g. assets/Patterns/hoody_mean_specification.json,
shirt_mean_specification.json) using the default sim config — not
specific to any custom pattern.

Fix

elif platform.system() in ["Linux", "OSX", "Darwin"]:

One-line change, confirmed working after patching: re-running the same
example patterns afterward gives real physics results (Static with 0 non-static vertices, proper collision counts, correctly-draped meshes)
instead of the silent no-op.

Environment

• macOS (Apple Silicon), Python 3.11
• Reproduced against both GarmentCode and the NvidiaWarp-GarmentCode fork
  built from source (CPU-only, no CUDA — which builds and runs fine on
  macOS, that part isn't the issue)