Update main.py

main.py

@@ -79,9 +79,10 @@ except Exception as e:
 #                     → gemini-3.1-flash-lite  (Gemini 3.1 Flash-Lite,
 #                       Google's most cost-efficient model as of May 2026)
 #
-#  GENERATION_MODEL : multimodal image+text generation
-#                     → gemini-3.1-flash-image-preview  (Nano Banana 2,
-#                       launched Feb 26 2026 as Gemini 3.1 Flash Image)
+#  GENERATION_MODEL : IMAGE OUTPUT ONLY (Nano Banana 2). It must always be
+#                     called with response_modalities=['Text', 'Image'] — a
+#                     text-only request against this model returns 400
+#                     INVALID_ARGUMENT. Never route text prompts here.
 #
 #  SUMMARY_MODEL    : lightweight text analysis for call briefings
 #                     → gemini-2.5-flash-lite  (replaces 2.0-flash-lite
@@ -317,7 +318,11 @@ def generate_tts_audio_and_upload(text_to_speak, uid, project_id, step_num):
 
 
 def send_text_request(model_name, prompt, image):
-    """Helper to send requests that expect only a text response."""
+    """Helper to send requests that expect only a text response.
+
+    Only pass text-capable models here (CATEGORY_MODEL, PLAN_TEXT_MODEL,
+    SUMMARY_MODEL). Image-output models reject text-only requests with 400.
+    """
     try:
         chat = client.chats.create(model=model_name)
         response = chat.send_message([prompt, image])
@@ -1375,7 +1380,11 @@ def create_project():
         INITIAL PLAN:
         [Your plan or 3 options]
         """
-        plan_response = send_text_request(GENERATION_MODEL, plan_prompt, pil_image)
+        # FIX (400 INVALID_ARGUMENT): this is a text-only response, so it must go
+        # to a text model. GENERATION_MODEL (gemini-3.1-flash-image-preview) is an
+        # image-output model that requires response_modalities=['Text','Image'];
+        # sending it a plain text chat rejects with 400 before generation begins.
+        plan_response = send_text_request(PLAN_TEXT_MODEL, plan_prompt, pil_image)
         if not plan_response:
             return jsonify({'error': 'Failed to generate project plan from AI.'}), 500