Add image upload in conversation

engine/config.py

@@ -148,6 +148,8 @@ class LLMConfig:
     variables: dict[str, str] = field(default_factory=dict)
     detail: bool = False
     timeout_sec: float = 60.0
+    # FastGPT image input mode: "base64" (inline data URL) or "upload" (presigned upload).
+    image_input_mode: str = "base64"
 
     @property
     def is_fastgpt(self) -> bool:
@@ -257,6 +259,15 @@ def config_from_dict(data: dict) -> EngineConfig:
         llm["app_id"] = None
     if not isinstance(llm.get("variables"), dict):
         llm["variables"] = {}
+    image_input_mode = str(
+        llm.get("image_input_mode", LLMConfig().image_input_mode)
+    ).strip().lower()
+    if image_input_mode not in {"base64", "upload"}:
+        raise ValueError(
+            "services.llm.image_input_mode must be 'base64' or 'upload', "
+            f"got {llm.get('image_input_mode')!r}"
+        )
+    llm["image_input_mode"] = image_input_mode
     if agent.get("greeting_mode") == "fastgpt_opener" and llm["provider"] != "fastgpt":
         raise ValueError(
             "agent.greeting_mode='fastgpt_opener' requires services.llm.provider='fastgpt'"