BeagleBone Black — follow-up target (not started)

M0 ships x86_64 (QEMU) and Raspberry Pi 3/4/5 images only. A BeagleBone Black Buildroot target is intentionally not-started in the M0 management closeout.

Intended later work (separate PR)

1. Confirm pinned Buildroot 2026.05.2 contains beaglebone_defconfig and read the board README before guessing artifact names.
2. Optional workflow_dispatch target beaglebone (32-bit ARMv7 hard-float), same routerd + React assets, Dropbear SSH recovery, manifests/checksums/legal-info.
3. Prove AtomicU64 and dependencies compile for that triple; handle libatomic explicitly if required — never silently weaken counters.
4. Keep BBB out of mandatory PR CI until build time and reliability are known.

Future MS/TP wiring (docs only — not implemented)

Path	Notes
A	Existing Waveshare USB-to-RS485-C at a USB endpoint
B	Preferred later: expansion-header UART + isolated 3.3 V RS-485 transceiver with kernel RS-485 direction control
C	PRU-based MS/TP timing is research only and must be driven by on-wire evidence

Do not flash physical media from CI. Do not claim hardware boot until demonstrated.