Update and Question
I attempted hacking device-os to get my hands on a particle::SerialStream pointing straight to HAL_USART_SERIAL2 so I could bypass all that Cellular.command() stuff and see whether its modem or upper layers, but it was a major pain because of linking failures, so I gave up.
I tried to use the simple AT Pass thru program to see what the modem has to say. Nothing but timeouts. The modem seems to be dead but I can’t tell if it’s the modem or something in an upper layer–but the problem is present on at least two modules, now, that have worked fine in the past.
Is there a way to get access to that serial port, from user space, and drop all the fanciness just so I can know whether the SARA is alive?