In Next 16, history.replaceState changes the URL but not useSearchParams: keep the open route in state of your own

a plain pushState(null, …) did update it: probed in the browser, the header switched to the chat named in the new URL. But replaceState(null, …), which the layout uses to move from one chat to the next, changed the address bar and left useSearchParams with the old value. Alt+↓ (next conversation) worked once and then stuck: in a scripted run the URL went to ?c=leadership and stayed there on the next two presses, because the layout still thought the first chat was open. The build notes add that handing Next's own history.state back to these calls, the first attempt, broke both.

the build's probes and scripted runs before and after; chat-layout.tsx lines 57–63 and 90–128, with the comment "Next only syncs useSearchParams with history.pushState".