fix sample upload blocking the event loop and causing server timeouts

Move audio validation and saving to thread pool so librosa/ffmpeg decoding
doesn't block the async event loop. Combine validate + load into a single
pass to avoid decoding the file twice. Add 50 MB upload limit and chunked
reads to prevent unbounded memory allocation.

Closes #278

backend/routes/profiles.py

@@ -102,6 +102,10 @@ async def delete_profile(
     return {"message": "Profile deleted successfully"}
 
 
+SAMPLE_MAX_FILE_SIZE = 50 * 1024 * 1024  # 50 MB
+SAMPLE_UPLOAD_CHUNK_SIZE = 1024 * 1024  # 1 MB
+
+
 @router.post("/profiles/{profile_id}/samples", response_model=models.ProfileSampleResponse)
 async def add_profile_sample(
     profile_id: str,
@@ -115,8 +119,16 @@ async def add_profile_sample(
     file_suffix = _uploaded_ext if _uploaded_ext in _allowed_audio_exts else ".wav"
 
     with tempfile.NamedTemporaryFile(suffix=file_suffix, delete=False) as tmp:
-        content = await file.read()
-        tmp.write(content)
+        total_size = 0
+        while chunk := await file.read(SAMPLE_UPLOAD_CHUNK_SIZE):
+            total_size += len(chunk)
+            if total_size > SAMPLE_MAX_FILE_SIZE:
+                Path(tmp.name).unlink(missing_ok=True)
+                raise HTTPException(
+                    status_code=413,
+                    detail=f"File too large (max {SAMPLE_MAX_FILE_SIZE // (1024 * 1024)} MB)",
+                )
+            tmp.write(chunk)
         tmp_path = tmp.name
 
     try:

backend/services/profiles.py

@@ -22,7 +22,7 @@ from ..database import (
     Generation as DBGeneration,
 )
 from ..models import EffectConfig
-from ..utils.audio import validate_reference_audio, load_audio, save_audio
+from ..utils.audio import validate_reference_audio, validate_and_load_reference_audio, load_audio, save_audio
 from ..utils.images import validate_image, process_avatar
 from ..utils.cache import _get_cache_dir, clear_profile_cache
 from .tts import get_tts_model
@@ -117,11 +117,16 @@ async def add_profile_sample(
     Returns:
         Created sample
     """
+    import asyncio
+
     profile = db.query(DBVoiceProfile).filter_by(id=profile_id).first()
     if not profile:
         raise ValueError(f"Profile {profile_id} not found")
 
-    is_valid, error_msg = validate_reference_audio(audio_path)
+    # Validate and load audio in a single pass, off the event loop
+    is_valid, error_msg, audio, sr = await asyncio.to_thread(
+        validate_and_load_reference_audio, audio_path
+    )
     if not is_valid:
         raise ValueError(f"Invalid reference audio: {error_msg}")
 
@@ -130,8 +135,7 @@ async def add_profile_sample(
     profile_dir.mkdir(parents=True, exist_ok=True)
 
     dest_path = profile_dir / f"{sample_id}.wav"
-    audio, sr = load_audio(audio_path)
-    save_audio(audio, str(dest_path), sr)
+    await asyncio.to_thread(save_audio, audio, str(dest_path), sr)
 
     db_sample = DBProfileSample(
         id=sample_id,

backend/utils/audio.py

@@ -217,22 +217,40 @@ def validate_reference_audio(
     Returns:
         Tuple of (is_valid, error_message)
     """
+    result = validate_and_load_reference_audio(
+        audio_path, min_duration, max_duration, min_rms
+    )
+    return (result[0], result[1])
+
+
+def validate_and_load_reference_audio(
+    audio_path: str,
+    min_duration: float = 2.0,
+    max_duration: float = 30.0,
+    min_rms: float = 0.01,
+) -> Tuple[bool, Optional[str], Optional[np.ndarray], Optional[int]]:
+    """
+    Validate and load reference audio in a single pass.
+    
+    Returns:
+        Tuple of (is_valid, error_message, audio_array, sample_rate)
+    """
     try:
         audio, sr = load_audio(audio_path)
         duration = len(audio) / sr
         
         if duration < min_duration:
-            return False, f"Audio too short (minimum {min_duration} seconds)"
+            return False, f"Audio too short (minimum {min_duration} seconds)", None, None
         if duration > max_duration:
-            return False, f"Audio too long (maximum {max_duration} seconds)"
+            return False, f"Audio too long (maximum {max_duration} seconds)", None, None
         
         rms = np.sqrt(np.mean(audio**2))
         if rms < min_rms:
-            return False, "Audio is too quiet or silent"
+            return False, "Audio is too quiet or silent", None, None
         
         if np.abs(audio).max() > 0.99:
-            return False, "Audio is clipping (reduce input gain)"
+            return False, "Audio is clipping (reduce input gain)", None, None
         
-        return True, None
+        return True, None, audio, sr
     except Exception as e:
-        return False, f"Error validating audio: {str(e)}"
+        return False, f"Error validating audio: {str(e)}", None, None