A switch can land on an older build: e.g. prod cannot read dev's /mqtt.json,
and prod's M7 image has no Ethernet. Each image carries an ota-compat tag
(state generation + transports). A switch is flashed without rebooting, the
new image's tag is read (bounded by its length), and boot is pointed back at
the running image unless the target keeps this node's state and transports.
CI now requires the tag in every published binary.
Every observer build now carries both channel URLs, so checking for a URL's
presence or absence can no longer tell prod from beta (and the old checks would
reject every build). Read the ota-base-* tags from every .bin in out/ instead
of a single ELF, with URLs shared by build.sh and both workflows.
agessaman