Update backend/lens_core.py

backend/lens_core.py

@@ -562,10 +562,29 @@ def _resolve_ai_config():
 
 def _openai_compat_generate_json(api_key: str, base_url: str, model: str, system_text: str, user_parts: list[str]):
     url = (base_url.rstrip("/") + "/chat/completions")
-    messages = [{"role": "system", "content": system_text}]
-    for p in user_parts:
-        if (p or "").strip():
-            messages.append({"role": "user", "content": p})
+
+    def _user_only_prompt_for_model(m: str) -> bool:
+        ml = (m or "").strip().lower()
+        if not ml:
+            return False
+        if "gemma-3" in ml or "gemma-2" in ml:
+            return True
+        if "gemma" in ml and ("-it" in ml or "instruct" in ml):
+            return True
+        return False
+
+    def _build_messages(m: str):
+        parts = [p.strip() for p in (user_parts or []) if isinstance(p, str) and p.strip()]
+        sys = (system_text or "").strip()
+        if _user_only_prompt_for_model(m):
+            combined = "\n\n".join([x for x in ([sys] + parts) if x])
+            return [{"role": "user", "content": combined}]
+        msgs = [{"role": "system", "content": system_text}]
+        for p in parts:
+            msgs.append({"role": "user", "content": p})
+        return msgs
+
+    messages = _build_messages(model)
     payload = {
         "model": model,
         "messages": messages,
@@ -597,6 +616,7 @@ def _openai_compat_generate_json(api_key: str, base_url: str, model: str, system
                     fallback = _pick_hf_fallback_model(models)
                     if fallback and fallback != model:
                         payload["model"] = fallback
+                        payload["messages"] = _build_messages(fallback)
                         used_model = fallback
                         r2 = client.post(url, json=payload, headers=headers)
                         try: