> There's no way a sensor can tell if a signal was from its own origin?

https://ui.adsabs.harvard.edu/abs/1978ntc.....2...18F/abstra...

https://apps.dtic.mil/sti/tr/pdf/ADA218226.pdf

> An increasingly popular modulation scheme is Binary Pseudo Random Phase Coding (BPRPC), whereby the phase of the transmitted signal is switched between 0 and 180 under the control of a binary pseudo random sequence

this applies straightforwardly to lidar

basically: optical CDMA or DSSS

spoofing replay may still be a concern