Port the abort-correctness pair from upstream sgl-project/sglang:
- #24522: abort() now calls kv_mgr.update_status(room, Failed) so the
transfer worker and other pollers observe the abort, not only the local
conclude_state.
- #27372 (guard half): the transfer worker skips a chunk whose room has
already failed or been aborted, so it never transfers into KV pages that
may have been reclaimed. This matters more once per-layer async transfer
widens the abort-vs-in-flight window.
The decode->prefill ABORT/ABORT_ACK notification half of #27372 is deferred:
it interleaves with staging/tracing infra this branch lacks and needs the PD
test harness to verify, so porting it now would be unverified guesswork.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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