The espressif ESP Thread Border Router was $20 on Amazon and I had ESP32-S3 and ESP32-H2 dev kits on hand so I put the two together for less than half that… plus a few hours to design this case.

| ESP32-S3 | ESP32-H2 (RCP) | Purpose |
|--|--|--|
| 7 | RST | RCP Reset |
| 8 | 9 | RCP Boot |
| 17 | 24 | RCP UART TX |
| 18 | 23 | RCP UART RX |
| 3.3V | 3.3V | Power (either this one or 5V) |
| GND | GND | Power Ground |

Note I wired to the H2's UART0 instead of the espressif default pins (and changed them in openthread/ot_rcp's menuconfig) and had to flash it manually before anything would work. The S3 is supposed to flash the H2 because it has the RCP firmware built in, but it never worked for me and I do not know how they think it will when the ROM bootloader will only take a UART upload from UART0.