--- baked-ours/v1/worker/gpu/attn_utils.py	2026-09-10 19:56:14.000000000 +0200
+++ baked/v1/worker/gpu/attn_utils.py	2026-09-11 10:13:47.000000000 +0200
@@ -20,6 +20,7 @@
     KVCacheConfig,
     KVCacheSpec,
     UniformTypeKVCacheSpecs,
+    is_dcp_replicated_spec,
 )
 from vllm.v1.worker.gpu.model_states.interface import ModelSpecificAttnMetadata
 from vllm.v1.worker.utils import (
@@ -283,6 +284,13 @@
     for i in range(num_kv_cache_groups):
         block_table = block_tables[i]
         slot_mapping = slot_mappings[i]
+        # DCP-replicated groups hold every position on every rank: their
+        # builders must see the full seq_lens, not this rank's shard.
+        group_dcp_local_seq_lens = (
+            None
+            if is_dcp_replicated_spec(kv_cache_config.kv_cache_groups[i].kv_cache_spec)
+            else dcp_local_seq_lens
+        )
         # Per-group causal for hybrid drafters (mixed SWA/full attention).
         group_causal = (
             causal if isinstance(causal, (bool, torch.Tensor)) else causal.get(i, True)
@@ -310,7 +318,7 @@
             block_table_tensor=block_table,
             slot_mapping=slot_mapping,
             causal=group_causal,
-            dcp_local_seq_lens=dcp_local_seq_lens,
+            dcp_local_seq_lens=group_dcp_local_seq_lens,
             positions=positions,
             is_prefilling=group_is_prefilling,
             mm_req_doc_ranges=mm_req_doc_ranges,