The router was fine. It routed. It had done so for two years without complaint, which in router terms is a long and honourable career. So naturally I decided it needed OpenWrt, because the stock firmware was "limiting me", by which I meant it was working and I was bored.
The flash itself went well, right up until it didn't. I picked the wrong image, near enough but not quite the right model variant, and watched the device go from blinking confidently to a single sullen LED that did nothing. Bricked. No web interface, no ping, no DHCP, no anything. The sort of silence that makes you go back and reread the very specific warning you skimmed twenty minutes earlier.
What saved it was that I'd soldered a serial header on months ago when I first opened the case, on the vague theory that I'd want it eventually. Past me, for once, did present me a favour. A USB-to-TTL adapter at 115200 baud got me a U-Boot prompt, and from there a TFTP recovery let me push the correct image and bring it back to life.
setenv ipaddr 192.168.1.1
setenv serverip 192.168.1.2
tftpboot 0x80000000 openwrt-correct-model.bin
It works now, on OpenWrt, doing the exact same job it did before, only now I understand it less reassuringly well. The lesson isn't "don't flash routers", because flashing routers is good fun. The lesson is solder the serial header on before you need it, read which exact model you actually own rather than the one that's nearly the same, and accept that some of the most satisfying afternoons are spent fixing problems you went out of your way to create.