Built a 4G feature phone around an ESP32-S3 and a Quectel EG912U-GL — the full duplex audio ate most of the spring

I run a small electronics company in Zagreb and this is our own kit, so read me as an interested party — the campaign for it is live right now. What I actually want to talk about is the audio path. Mic is an SPH0645, output is a MAX98357A, both on I2S0, and getting them running at the same time while the modem sprays unsolicited output at the UART took longer than the keypad, display and SMS stack put together.

If you've done full duplex on an S3 — one I2S peripheral for both directions, or split them? And how do you keep the modem's URCs out of your response parser?