feat(insta-lab): card_renderer theme 폴백 가드 (HTML 없으면 default)

insta-lab/app/card_renderer.py

@@ -6,6 +6,7 @@ import json
 import logging
 import os
 import tempfile
+from pathlib import Path
 from typing import List
 
 from jinja2 import Environment, FileSystemLoader, select_autoescape
@@ -67,6 +68,13 @@ async def render_slate(slate_id: int, template: str = "default/card.html.j2") ->
     if not slate:
         raise ValueError(f"slate {slate_id} not found")
     env = _env()
+
+    # template 파일이 없으면 default로 폴백 (INSTA_DEFAULT_THEME가 import 안 된 theme이면 안전)
+    template_full = Path(_resolve_template_dir()) / template
+    if not template_full.exists():
+        logger.warning("Template '%s' 없음 → 'default/card.html.j2'로 폴백", template)
+        template = "default/card.html.j2"
+
     tmpl = env.get_template(template)
     pages = _build_pages(slate)
     out_dir = _slate_dir(slate_id)