### What this PR does / why we need it?
This PR fixes a critical bug in the PD-separated inference pipeline
where KV cache on the Prefill (P) side was not being properly released.
The issue arises when multiple clients use the same x-request-id: to
avoid request ID collisions, both Prefill and Decode nodes append a
random suffix to the incoming x-request-id. A previous PR ensured
consistency by having the P-side pass its final request_id as
remote_request_id to the D-side via kv_transfer_param. However, during
KV cache cleanup, the D-side incorrectly used the local req_id (instead
of remote_request_id) to select the target P-side rank. This mismatch
caused the P-side KV cache to remain unreleased on certain ranks,
leading to memory leaks. This PR corrects the logic to use
remote_request_id consistently when determining the P-side rank.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
The fix was validated by running multiple concurrent benchmark instances
- vLLM version: v0.14.1
- vLLM main:
dc917cceb8
Signed-off-by: ghphotoframe <854746559@qq.com>
41a52beb26