[claudesquad] update from 'debug_chunk-2' on 07 Jan 26 03:27 CST

nanovllm/layers/attention.py

@@ -104,6 +104,10 @@ class Attention(nn.Module):
             # This ensures proper synchronization with per-layer offload
             compute_stream = context.kvcache_manager.offload_engine.compute_stream
             if k_cache.numel() and v_cache.numel():
+                # CRITICAL: Wait for default stream to ensure slot_mapping tensor transfer is complete
+                # slot_mapping is created with non_blocking=True on default stream, but we use it
+                # on compute_stream. Without this sync, index_copy_ can get corrupted indices.
+                compute_stream.wait_stream(torch.cuda.default_stream())
                 with torch.cuda.stream(compute_stream):
                     store_kvcache(k, v, k_cache, v_cache, context.slot_mapping)
         else: