global key concurrency problem

app.py

@@ -70,12 +70,13 @@ async def process_fal_request(request_id, model_endpoint, fal_arguments, api_key
         print(f"[DEBUG] Model endpoint: {model_endpoint}")
         print(f"[DEBUG] Arguments: {json.dumps(fal_arguments, indent=2)[:500]}...")  # First 500 chars
         
-        # Set API key for this request
-        os.environ['FAL_KEY'] = api_key
-        
-        # Submit the request asynchronously
-        print(f"[DEBUG] Submitting to FAL API...")
-        handler = await fal_client.submit_async(
+        # Build per-request client with explicit key to avoid global env mutation
+        print(f"[DEBUG] Creating AsyncClient with per-request key (not using env var)")
+        client = fal_client.AsyncClient(key=api_key)
+
+        # Submit the request asynchronously using the per-request client
+        print(f"[DEBUG] Submitting to FAL API via AsyncClient.submit...")
+        handler = await client.submit(
             model_endpoint,
             arguments=fal_arguments,
         )
@@ -392,8 +393,9 @@ def upload_file():
 
 async def upload_file_to_fal_async(file_path, api_key):
     """Helper function to upload a file to FAL storage"""
-    os.environ['FAL_KEY'] = api_key
-    return await fal_client.upload_file_async(file_path)
+    # Use per-request AsyncClient with explicit key to avoid global env mutation
+    client = fal_client.AsyncClient(key=api_key)
+    return await client.upload_file(file_path)
 
 def upload_to_fal_sync(file_path, api_key):
     """Run upload coroutine on the shared background event loop"""