feat: add voice studio prototype flow

backend/app/services/voice_session_storage.py

@@ -26,6 +26,38 @@ def build_turn_assistant_audio_path(session_id: str, turn_index: int) -> Path:
     return session_storage_dir(session_id) / f"turn-{turn_index:03d}-assistant.mp3"
 
 
+def _normalize_audio_suffix(file_name: str | None, mime_type: str | None) -> str:
+    if file_name and "." in file_name:
+        return file_name.rsplit(".", 1)[-1].lower()
+
+    if mime_type == "audio/webm":
+        return "webm"
+    if mime_type == "audio/wav":
+        return "wav"
+    if mime_type == "audio/mpeg":
+        return "mp3"
+    if mime_type == "audio/mp4":
+        return "m4a"
+    return "bin"
+
+
+def write_uploaded_user_audio(
+    *,
+    session_id: str,
+    turn_index: int,
+    file_name: str | None,
+    mime_type: str | None,
+    audio_data: bytes,
+) -> str:
+    """Persist one uploaded user-audio turn and return the saved file path."""
+
+    suffix = _normalize_audio_suffix(file_name, mime_type)
+    return write_session_audio(
+        build_turn_user_audio_path(session_id, turn_index, suffix),
+        audio_data,
+    )
+
+
 def write_session_audio(path: Path, audio_data: bytes) -> str:
     """Persist session audio bytes atomically and return the saved path."""