[Bugfix] Fix Qwen3-Omni streaming crops in mixed-length batches (#7340)

Signed-off-by: Deep Shah <deep@socratic.co>

vllm_omni/model_executor/models/qwen3_omni/qwen3_omni_code2wav.py

@@ -316,21 +316,16 @@ class Qwen3OmniMoeCode2Wav(nn.Module, Qwen3OmniNestedSupportsQuant):
         else:
             # Fallback: assume all batch elements share the same sequence length.
             code_seq_lens = [codes.shape[-1]] * codes.shape[0]
+        # The decoder trims the same right-edge tail from every batch row.
+        # Infer it from the decoded window, not a shorter request's length:
+        # padding that request with codec zeros does not provide valid context.
+        tail = max(0, int(codes.shape[-1] * self.total_upsample) - batch_wav.shape[-1])
         for idx, code_seq_len in enumerate(code_seq_lens):
-            # The eager decoder (self(codes)) emits a fixed `tail` fewer samples than
-            # code_seq_len*total_upsample: the causal conv stack trims the sequence end
-            # because it lacks right context. The original slice assumed full length, so
-            # under async_chunk every streaming chunk silently dropped its last `tail`
-            # samples -> a ~23ms gap at every chunk boundary + cumulative ~1.2% time
-            # compression. Shift the start back by `tail` so this chunk refills the gap the
-            # previous chunk left (those frames are re-decoded here with proper context).
-            # `tail` is measured per call, so this is a no-op only when the decoder returns
-            # the nominal full length (tail==0, e.g. a C==0 decoder like Qwen3-TTS); for
-            # Qwen3-Omni Code2Wav both the eager forward AND the CUDA-graph wrapper
-            # (_trim_replay_output -> actual*upsample - 555) are short, so it applies to both.
-            tail = max(0, int(code_seq_len * self.total_upsample) - batch_wav.shape[-1])
+            # Refill the previous chunk's tail using the re-decoded left context,
+            # and exclude the current row's padded tail just as singleton decode does.
             start = max(0, left_context_size[idx] * self.total_upsample - tail)
-            wav_chunk = batch_wav[idx, :, start : code_seq_len * self.total_upsample]
+            end = max(0, code_seq_len * self.total_upsample - tail)
+            wav_chunk = batch_wav[idx, :, start:end]
             wavs.append(wav_chunk)
         return wavs