Cold App Router SSR requests currently share Vite RSC's underlying module import promises, but each request can still iterate the full client-reference manifest and allocate its own Promise.all fan-out before the completed boolean flips. That keeps first-request correctness but wastes work during cold bursts.
The preload state only tracked completion, not in-flight work. Concurrent callers had no shared promise to await, and the preload logic lived inline in the SSR entry where the concurrency contract was hard to test.
Add a typed client-reference preloader that shares the global manifest preload promise, dedupes per-reference work for future scoped manifests, preserves non-fatal reference load reporting, and keeps handleSsr awaiting the preload before React consumes the Flight stream.
Nathan Nguyen