Fix vision attachment timeout and stale cache

Increase local vision model timeout and avoid caching transient VL failure placeholders.\n\nCloses #202.

src/chat_handler.py

@@ -223,17 +223,20 @@ class ChatHandler:
                         if os.path.exists(_vcache):
                             try:
                                 with open(_vcache) as _vf:
-                                    vl_desc = _vf.read()
+                                    cached_desc = _vf.read().strip()
+                                if cached_desc and not cached_desc.startswith("["):
+                                    vl_desc = cached_desc
                             except Exception:
                                 vl_desc = None
                         if not vl_desc:
                             vl_result = analyze_image_with_vl_result(file_info["path"])
                             vl_desc = vl_result.get("text", "")
                             vl_model = vl_result.get("model", "")
+                            if vl_desc and not vl_desc.startswith("["):
                                 try:
                                     os.makedirs(os.path.join(UPLOAD_DIR, ".vision"), exist_ok=True)
                                     with open(_vcache, "w") as _vf:
-                                    _vf.write(vl_desc or "")
+                                        _vf.write(vl_desc)
                                 except Exception:
                                     pass
                         enhanced_message = f"{enhanced_message}\n\n[Image: {file_info['name']}]\n{vl_desc}"

src/document_processor.py

@@ -230,7 +230,7 @@ def analyze_image_with_vl_result(image_path: str) -> dict:
         last_err = None
         for i, (_url, _model, _headers) in enumerate([c for c in _vl_candidates if c and c[0] and c[1]]):
             try:
-                description = llm_call(_url, _model, vl_messages, headers=_headers, timeout=30)
+                description = llm_call(_url, _model, vl_messages, headers=_headers, timeout=120)
                 logger.info("VL analysis complete with model %s", _model)
                 return {"text": description, "model": _model}
             except Exception as e: