[Bugfix][Qwen3-TTS] Handle codec generations that exhaust their token budget (#6728)

Signed-off-by: Sy03 <1370724210@qq.com>

tests/engine/test_orchestrator.py

@@ -2292,7 +2292,12 @@ def test_stage_pool_metrics_use_resumable_segment_token_count() -> None:
     )
     output = SimpleNamespace(
         request_id="req-stream",
-        outputs=[SimpleNamespace(cumulative_token_ids=list(range(11)))],
+        outputs=[
+            SimpleNamespace(
+                cumulative_token_ids=list(range(11)),
+                finish_reason=FinishReason.LENGTH,
+            )
+        ],
     )
 
     metrics = pool.build_stage_metrics(
@@ -2304,6 +2309,7 @@ def test_stage_pool_metrics_use_resumable_segment_token_count() -> None:
 
     assert metrics.num_tokens_out == 3
     assert metrics.output_unit_count == 3
+    assert metrics.finish_reason == "length"
 
 
 def test_image_ttfo_preserves_request_time_and_tracks_stage_time() -> None: