Replace pip-resolved sglang==0.5.10 with an editable install from
third_party/sglang/python. The vendored fork carries patches the pip
release does not (admit_direct_append RPC types, _should_allow_local_
prefill_on_decode, maybe_trim_decode_session_cache, backpressure pause
hint) — KVC routing depends on them, so the vendored copy must be the
import target, not just on PYTHONPATH at runtime.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
