[BugFix] Fix async scheduling + chunked prefill + preemption (#28787)

Signed-off-by: Nick Hill <nhill@redhat.com>

vllm/v1/core/sched/scheduler.py

@@ -778,9 +778,7 @@ class Scheduler(SchedulerInterface):
                 assert not scheduled_in_prev_step
                 resumed_req_ids.add(req_id)
             if not scheduled_in_prev_step:
-                all_token_ids[req_id] = req.all_token_ids[
-                    : req.num_computed_tokens + num_tokens
-                ]
+                all_token_ids[req_id] = req.all_token_ids.copy()
             new_block_ids.append(
                 req_to_new_blocks[req_id].get_block_ids(allow_none=True)
             )

vllm/v1/utils.py

@@ -97,6 +97,9 @@ class ConstantList(Generic[T], Sequence):
     def __repr__(self):
         return f"ConstantList({self._x})"
 
+    def copy(self) -> list[T]:
+        return self._x.copy()
+
 
 class CpuGpuBuffer:
     """Buffer to easily copy tensors between CPU and GPU."""