[Bugfix] Missing NIXL metadata for handshake initialization if instance spans multi-node (#26338)

Signed-off-by: Guan Luo <gluo@nvidia.com>
Signed-off-by: GuanLuo <41310872+GuanLuo@users.noreply.github.com>
Signed-off-by: Guan Luo <41310872+GuanLuo@users.noreply.github.com>
Co-authored-by: Nicolò Lucchesi <nlucches@redhat.com>

vllm/v1/worker/gpu_worker.py

@@ -19,7 +19,11 @@ from vllm.distributed import (
     init_distributed_environment,
     set_custom_all_reduce,
 )
-from vllm.distributed.kv_transfer import ensure_kv_transfer_initialized
+from vllm.distributed.kv_transfer import (
+    ensure_kv_transfer_initialized,
+    get_kv_transfer_group,
+    has_kv_transfer_group,
+)
 from vllm.distributed.parallel_state import (
     get_pp_group,
     get_tp_group,
@@ -348,6 +352,21 @@ class Worker(WorkerBase):
 
         return int(self.available_kv_cache_memory_bytes)
 
+    def get_kv_connector_handshake_metadata(self) -> dict | None:
+        """Get KV connector metadata from this worker if available."""
+
+        if not has_kv_transfer_group():
+            return None
+
+        connector = get_kv_transfer_group()
+        # Return None for connectors that don't need to exchange handshake
+        # metadata across workers.
+        if (metadata := connector.get_handshake_metadata()) is None:
+            return None
+
+        tp_rank = get_tp_group().rank_in_group
+        return {tp_rank: metadata}
+
     def get_kv_cache_spec(self) -> dict[str, KVCacheSpec]:
         return self.model_runner.get_kv_cache_spec()