Root cause: each vLLM instance has a random NONE_HASH (os.urandom(32))
when PYTHONHASHSEED is not set. All block hashes are chained from
NONE_HASH, so D's hashes never match C's hashes.
Fix: C's bootstrap server now accepts token_ids and does the prefix
cache lookup locally using C's own hash function and block pool.
No cross-instance hash matching needed.
New flow: D sends prompt token_ids → C computes hashes on C's side →
C looks up in C's own BlockPool → returns block_ids.
Also: module-level _shared_block_pool for scheduler→bootstrap bridge,
prompt_token_ids passed through PullReqMeta, test script added.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
