vLLM's first AuxOutput connector stores MoE routed-expert IDs under KV-compatible block hashes.

PR #45635 adds routed-expert output as the first auxiliary type, and the design note explains why the obvious approach fails: R3 can't be a request-local GPU buffer once prefix caching and async scheduling are on, because a cache hit skips execution, GPU slots aren't stable identities, and speculative decoding executes rows that get rejected. Storing immutable R3 blocks under KV-compatible hashes lets KV and R3 for the same prefix be reused together. Ships a bounded local shared-memory backend, with distributed storage named as follow-up.