[Mooncake] Guard partial-hit revalidation

Skip the exact-key retry when a cache pool has no existence oracle or the layout has no full-attention group. Add regression coverage for both paths and make long hash fixtures wrap their byte values.

Co-authored-by: OpenAI Codex <noreply@openai.com>

Author: 2 people

tests/v1/kv_connector/unit/test_mooncake_store_coordinator.py

@@ -106,7 +106,7 @@ def _swa(block_size=16, sliding_window=32):
 
 
 def _hashes(n: int) -> list[BlockHash]:
-    return [BlockHash(bytes([i + 1]) * 4) for i in range(n)]
+    return [BlockHash((i + 1).to_bytes(4, byteorder="little")) for i in range(n)]
 
 
 # ----- Single-group coordinator -----
@@ -278,6 +278,35 @@ def test_coordinator_revalidates_reconciled_partial_tail_key():
     assert hit == 32
 
 
+def test_exact_partial_hit_retry_skips_pool_without_existence_data(monkeypatch):
+    groups = [
+        KVCacheGroupSpec(["L0"], _full(32)),
+        KVCacheGroupSpec(["L1"], _mamba_align(32)),
+    ]
+    coord = _make_coord(groups, hash_block_size=16)
+    hs = _hashes(4)
+    cmap = ExternalCachedBlockPool(16)
+
+    def fail_lookup(*_args, **_kwargs):
+        pytest.fail("receive-side pool has no existence data to revalidate")
+
+    monkeypatch.setattr(cmap, "get_cached_block", fail_lookup)
+
+    assert coord._exact_partial_hit_key_exists(hs, 48, cmap)
+
+
+def test_partial_hash_hit_without_full_attention_does_not_revalidate():
+    groups = [KVCacheGroupSpec(["L0"], _mamba_align(32))]
+    coord = _make_coord(groups, hash_block_size=16)
+    hs = _hashes(4)
+    cmap = ExternalCachedBlockPool(16, {(0, bytes(hs[2]))})
+
+    masks, hit = coord.find_longest_cache_hit(hs, max_length=64, cached_block_pool=cmap)
+
+    assert hit == 48
+    assert masks == ([False, True],)
+
+
 # ----- store_mask -----
 
 

vllm/distributed/kv_transfer/kv_connector/v1/mooncake/store/coordinator.py

@@ -37,6 +37,8 @@ def __init__(
         # determined and we just want each spec's manager to apply its own mask.
         self._exists = exists
         self.hash_block_size = hash_block_size
+        # Recv-side pools cannot verify whether an exact key exists.
+        self.tracks_existence = exists is not None
         self.null_block = KVCacheBlock(block_id=0)
         # Dummy ID 1 for present block for duck-typing.
         self._present_block = KVCacheBlock(block_id=1)
@@ -188,13 +190,18 @@ def _exact_partial_hit_key_exists(
         """Whether the reconciled partial FullAttention tail can be loaded."""
         if not self.enable_partial_hash_hits:
             return True
+        if not cached_block_pool.tracks_existence:
+            # Shortening here would desynchronize the mask from token_len.
+            return True
 
         # Attribute access, not tuple unpacking: SpecGroup carries manager_cls
         # and use_eagle here, so the upstream 3-tuple unpack raises ValueError
         # on the first lookup. git apply cannot see that -- it is a runtime
         # arity mismatch, not a textual conflict.
         group = self.attention_groups[0]
-        assert isinstance(group.spec, FullAttentionSpec)
+        if not isinstance(group.spec, FullAttentionSpec):
+            # Recurrent-only layouts have no FullAttention key to revalidate.
+            return True
         hash_idx = hit_length // self.hash_block_size - 1
         return (
             cached_block_pool.get_cached_block(block_hashes[hash_idx], group.group_ids)