Serial uploader was crashing the Pico when launching games because
it accessed SD card (SPI) while Core 1 was refreshing display (also SPI).
Display and SD card share the same SPI bus and cannot be accessed
simultaneously.
Split game launch into prepare and execute phases:
- prepare: Re-scan games directory (safe, SD access done immediately)
- execute: Load Lua script from SD (deferred until display is idle)
Main loop now checks !is_refresh_in_progress() before completing
launch, preventing SPI conflicts.
Also updated SD card best practices skill to document SPI bus
contention as the #1 most critical issue to avoid.
Co-Authored-By: Claude <noreply@anthropic.com>
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