The backend IP baked into a push-capable device at assign time is
auto-derived by subnet-matching a local NIC. That's non-deterministic
when two NICs match the device subnet, and null when none does. Surface
it: backendIpCandidates() lists all local IPv4 NICs (on-subnet first),
GET /api/setup/backend-ips serves them, and the wizard renders an
editable Backend push IP dropdown after a successful test (pre-filled
with the auto-pick, warns when no NIC is on the device subnet). The
chosen IP overrides the auto-pick on assign and is recorded in config.
julian
382c32f2bc