[Diffusion][HunyuanImage3] Add request paged prefix caching (#7719)

Signed-off-by: zwhzzz0821 <2831474076@qq.com>

tests/diffusion/diffusion_kv/test_request.py

@@ -4,8 +4,10 @@
 import pytest
 import torch
 import vllm.v1.core.single_type_kv_cache_manager as native_kv_managers
+from vllm.multimodal.inputs import MultiModalFeatureSpec, PlaceholderRange
+from vllm.utils.hashing import get_hash_fn_by_name
 from vllm.v1.core.kv_cache_manager import KVCacheManager
-from vllm.v1.core.kv_cache_utils import BlockHash
+from vllm.v1.core.kv_cache_utils import BlockHash, init_none_hash
 from vllm.v1.kv_cache_interface import (
     FullAttentionSpec,
     KVCacheConfig,
@@ -49,6 +51,51 @@ def test_request_exposes_native_request_and_diffusion_semantics() -> None:
     assert request.status is RequestStatus.WAITING
 
 
+def test_request_builds_only_full_prefix_block_hashes() -> None:
+    hash_function = get_hash_fn_by_name("sha256")
+    init_none_hash(hash_function)
+    request = _request(
+        prefix_len=6,
+        target_len=2,
+        cache_token_ids=range(6),
+        mm_features=[
+            MultiModalFeatureSpec(
+                data=None,
+                modality="image",
+                identifier="tail",
+                mm_position=PlaceholderRange(offset=4, length=2),
+            )
+        ],
+    )
+
+    request.build_block_hashes(BLOCK_SIZE, hash_function)
+
+    assert len(request.block_hashes) == 1
+    assert request.skip_reading_prefix_cache is False
+
+
+def test_changed_multimodal_identity_changes_the_block_hash() -> None:
+    hash_function = get_hash_fn_by_name("sha256")
+    init_none_hash(hash_function)
+    first = _request(cache_token_ids=range(4))
+    second = _request(
+        cache_token_ids=range(4),
+        mm_features=[
+            MultiModalFeatureSpec(
+                data=None,
+                modality="image",
+                identifier="image-a",
+                mm_position=PlaceholderRange(offset=2, length=2),
+            )
+        ],
+    )
+
+    first.build_block_hashes(BLOCK_SIZE, hash_function)
+    second.build_block_hashes(BLOCK_SIZE, hash_function)
+
+    assert first.block_hashes != second.block_hashes
+
+
 @pytest.mark.parametrize(
     ("overrides", "message"),
     [