$POVRID,1,GYRO_RESET,FORCE_CALIBRATE,00*3A

He sent it once. Twice. The rogue module stuttered. Its fake stream glitched. For a single second, the real gyro data broke through: $PROMT,1,ROLL,0.0,N,OK*1F

The checksum hex values, converted to ASCII, spelled:

Lin let out a breath she didn’t know she’d been holding. “You killed it with a single sentence.”

A three-point-four-degree roll. Critical. The city was listing toward the acid sea.

$PROMT,1,ROLL,-3.4,D,CRIT*2A

“Someone injected a false horizon,” Kaelen said, voice low. “They’re using NMEA 4.11’s biggest flaw: no authentication. Any device that speaks the sentence structure gets heard.”

Not a treaty or a code of law, but a protocol—the last agreed-upon standard for data exchange between sensors, actuators, and the city’s failing core. NMEA 4.11 was old, clunky, and verbose. It sent sentences like $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47 through rusting wires. But it was reliable. It was the only thing still speaking to the ancient navigation systems after the Great Static Burn wiped out all wireless comms.