[2/2] Support deterministic inference for temperature > 0 (#10678)

Co-authored-by: Baizhou Zhang <sobereddiezhang@gmail.com>
Co-authored-by: hebiao064 <hebiaobuaa@gmail.com>

python/sglang/srt/model_executor/model_runner.py

@@ -2049,7 +2049,6 @@ class ModelRunner:
             )
 
         self._preprocess_logits(logits_output, forward_batch.sampling_info)
-
         # Sample the next tokens
         next_token_ids = self.sampler(
             logits_output,
@@ -2057,6 +2056,12 @@ class ModelRunner:
             forward_batch.return_logprob,
             forward_batch.top_logprobs_nums,
             forward_batch.token_ids_logprobs,
+            # For prefill, we only use the position of the last token.
+            (
+                forward_batch.positions
+                if forward_batch.forward_mode.is_decode()
+                else forward_batch.seq_lens - 1
+            ),
         )
         return next_token_ids