Fix directory creation on Windows

[austinkimchi]

Issue

single_layer_sim.py creates layer directories using a shell mkdir command built from the output path.

On Windows, this can fail when the path contains spaces, such as My Path, resulting in the message The syntax of the command is incorrect.

Fixes

This replaces the shell-based mkdir call with os.makedirs(..., exist_ok=True).

This also removes the separate os.path.isdir check because os.makedirs(..., exist_ok=True) already handles both cases:

• creates the directory if it does not exist
• does nothing if the directory already exists

Resources

[Copilot]

Pull request overview

This PR improves cross-platform trace output by replacing a shell-based mkdir invocation in single_layer_sim.py with Python’s built-in directory creation (os.makedirs(..., exist_ok=True)), fixing failures on Windows when output paths contain spaces.

Changes:

• Replace os.system('mkdir ...') with os.makedirs(..., exist_ok=True) for layer trace directory creation.
• Remove the redundant os.path.isdir pre-check since exist_ok=True handles the “already exists” case.

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