fix(elevenlabs/stt): synthesize single-channel transcripts for mono responses

A mono Scribe response has raw words but no transcripts array; the OpenAI-format
words we map are lossy (text->word, spacing/punctuation dropped), so callers that
segment bubbles from raw per-word tokens got an empty transcript for mono audio.
Wrap the raw words as a one-channel transcripts entry. Non-breaking: multichannel
and OpenAI-compat words unchanged.

litellm/llms/elevenlabs/audio_transcription/transformation.py

@@ -162,6 +162,16 @@ class ElevenLabsAudioTranscriptionConfig(BaseAudioTranscriptionConfig):
             transcripts = response_json.get("transcripts")
             if isinstance(transcripts, list):
                 response["transcripts"] = transcripts
+            elif isinstance(response_json.get("words"), list):
+                # Single-channel (mono) response: no `transcripts` array, only flat
+                # top-level `words`. The OpenAI-format `response["words"]` above is
+                # lossy — it renames `text`->`word` and drops spacing/punctuation and
+                # audio events. Wrap the RAW words as one channel so callers get the
+                # same verbatim per-word tokens as multichannel and can segment
+                # bubbles uniformly; without this a mono transcript loses punctuation.
+                response["transcripts"] = [
+                    {"channel_index": 0, "words": response_json["words"]}
+                ]
 
             # Carry the billed audio duration (present on both single- and
             # multi-channel responses) so callers can attribute cost.

tests/test_litellm/llms/elevenlabs/audio_transcription/test_elevenlabs_audio_transcription_transformation.py

@@ -75,3 +75,36 @@ def test_response_single_channel_is_unchanged():
 
     assert response.text == "hello world"
     assert "transcripts" not in response.model_dump()
+
+
+def test_response_mono_words_synthesize_raw_single_channel():
+    """A mono (single-channel) response carries raw ``words`` but no ``transcripts``.
+    We synthesize a one-channel ``transcripts`` entry holding the RAW words verbatim
+    (``text``/``type``/spacing preserved), so callers get the same per-word tokens as
+    multichannel. The lossy OpenAI-format ``words`` (renamed ``word``, punctuation
+    dropped) stays too for OpenAI-compat consumers."""
+    config = ElevenLabsAudioTranscriptionConfig()
+
+    payload = {
+        "text": "hello world",
+        "language_code": "en",
+        "audio_duration_secs": 1.5,
+        "words": [
+            {"text": "hello", "start": 0.0, "end": 0.4, "type": "word"},
+            {"text": " ", "start": 0.4, "end": 0.5, "type": "spacing"},
+            {"text": "world", "start": 0.5, "end": 0.9, "type": "word"},
+        ],
+    }
+
+    response = config.transform_audio_transcription_response(_response(payload))
+
+    # Synthesized single channel with the RAW words (spacing + type intact).
+    assert [t["channel_index"] for t in response["transcripts"]] == [0]
+    raw = response["transcripts"][0]["words"]
+    assert [w["text"] for w in raw] == ["hello", " ", "world"]
+    assert [w["type"] for w in raw] == ["word", "spacing", "word"]
+    # OpenAI-format words unchanged: only real words, renamed key, no spacing.
+    assert response["words"] == [
+        {"word": "hello", "start": 0.0, "end": 0.4},
+        {"word": "world", "start": 0.5, "end": 0.9},
+    ]