[PD] Respect sampling_params.max_new_tokens when PD disaggregation is activated (#7598)

Signed-off-by: Shangming Cai <caishangming@linux.alibaba.com>

python/sglang/srt/disaggregation/decode.py

@@ -604,9 +604,21 @@ class DecodeTransferQueue:
                             : decode_req.req.top_logprobs_num
                         ].tolist()
                     )
+
                 if hasattr(decode_req.kv_receiver, "clear"):
                     decode_req.kv_receiver.clear()
+
+                # special handling for sampling_params.max_new_tokens == 1
+                if decode_req.req.sampling_params.max_new_tokens == 1:
+                    # finish immediately
+                    decode_req.req.check_finished()
+                    self.scheduler.stream_output(
+                        [decode_req.req], decode_req.req.return_logprob
+                    )
+                    self.tree_cache.cache_finished_req(decode_req.req)
+                else:
                     transferred_reqs.append(decode_req.req)
+
                 indices_to_remove.add(i)
             elif poll in [
                 KVPoll.Bootstrapping,