fix: pass size to ArraysCache in BatchMambaCache for Qwen3.5 hybrid models

vllm_mlx/utils/mamba_cache.py

@@ -12,17 +12,12 @@
 
 import mlx.core as mx
 
-# MambaCache was removed in mlx-lm 0.30.6 - make import conditional
+# MambaCache was removed in mlx-lm 0.30.6, fall back to ArraysCache
 try:
     from mlx_lm.models.cache import MambaCache
-
-    HAS_MAMBA_CACHE = True
 except ImportError:
-    # Fallback for mlx-lm >= 0.30.6 where MambaCache was removed
     from mlx_lm.models.cache import ArraysCache as MambaCache
 
-    HAS_MAMBA_CACHE = False
-
 logger = logging.getLogger(__name__)
 
 
@@ -42,10 +37,9 @@ def __init__(self, left_padding: Optional[List[int]] = None, size: int = 2):
             left_padding: Amount of left padding for each sequence in batch
             size: Number of state arrays (default 2 for Mamba models)
         """
-        if HAS_MAMBA_CACHE:
-            super().__init__(left_padding=left_padding)
-        else:
-            super().__init__(size=size, left_padding=left_padding)
+        # Always pass size - ArraysCache requires it, and MambaCache
+        # (if it exists) inherits from ArraysCache
+        super().__init__(size=size, left_padding=left_padding)
         self._batch_size = len(left_padding) if left_padding else 0
 
     def extract(self, idx: int) -> MambaCache:
@@ -59,10 +53,7 @@ def extract(self, idx: int) -> MambaCache:
             A new MambaCache with the extracted state
         """
         size = len(self.cache)
-        if HAS_MAMBA_CACHE:
-            cache = MambaCache()
-        else:
-            cache = MambaCache(size=size)
+        cache = MambaCache(size=size)
         # Extract the state arrays for this index
         cache.cache = [
             mx.contiguous(c[idx : idx + 1]) if c is not None else None