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

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

vllm_omni/diffusion/diffusion_kv/model_runner_backend.py

@@ -4,7 +4,7 @@
 from __future__ import annotations
 
 import copy
-from collections.abc import Mapping
+from collections.abc import Mapping, Sequence
 from dataclasses import dataclass
 from typing import Any
 
@@ -154,6 +154,7 @@ class DiffusionKVModelRunnerBackend:
 
         if attention_geometry is not None:
             num_heads, num_kv_heads, head_size = attention_geometry
+            assert callable(set_attention_geometry)
             try:
                 set_attention_geometry(
                     num_heads=num_heads,
@@ -396,6 +397,15 @@ class DiffusionKVModelRunnerBackend:
         for sequence in metadata.sequences:
             if type(sequence.sequence_id) is not int or sequence.sequence_id < 0:
                 raise ValueError(f"Diffusion KV sequence_id must be a non-negative integer: {sequence.sequence_id!r}")
+            if (
+                type(sequence.cached_prefix_len) is not int
+                or sequence.cached_prefix_len < 0
+                or sequence.cached_prefix_len > sequence.prefix_len
+            ):
+                raise ValueError(
+                    "Diffusion KV cached_prefix_len must lie within the stable prefix: "
+                    f"cached={sequence.cached_prefix_len!r}, prefix={sequence.prefix_len!r}"
+                )
             sequence_identity = (metadata.request_id, sequence.sequence_id, None)
             sequence_install = self._validate_row(
                 identity=sequence_identity,
@@ -410,6 +420,7 @@ class DiffusionKVModelRunnerBackend:
                     sequence.prefix_len,
                     sequence.target_len,
                     sequence.seq_len,
+                    sequence.cached_prefix_len,
                     sequence_install.block_ids,
                     sequence.context_ids,
                 )
@@ -593,7 +604,7 @@ class DiffusionKVModelRunnerBackend:
                     )
         raise RuntimeError(f"Diffusion KV request state is missing logical length for {identity!r}")
 
-    def remove_diffusion_kv_requests(self, request_ids: list[str | tuple[str, int]]) -> int:
+    def remove_diffusion_kv_requests(self, request_ids: Sequence[str | tuple[str, int]]) -> int:
         """Retire Worker rows without logically freeing Scheduler-owned blocks."""
         if (
             not is_scheduler_paged_kv_mode(