2× Radeon AI PRO R9700 (RDNA4/gfx1201) on vLLM 0.22.1 — how we fixed the long-context decode cliff (and what we learned chasing FP8)

Posting our setup for the (apparently growing) club of people running multiple R9700s on vLLM. Big shout-out to u/AustinM731 — their AITER Unified Attention post was the single most useful thing we found, and I want to (a) confirm it works, (b) share where our findings lined up vs differed, and (c)