Enhance client mode handling in ProcessRequest_chat

- Introduced a normalization function for client mode to default to "direct" when input is empty or None.
- Updated the clientMode field to use a new type with BeforeValidator for improved validation.
- Added a test to ensure empty client mode inputs correctly default to "direct".

src/schemas/models.py

@@ -1,13 +1,22 @@
-from pydantic import BaseModel, Field
-from typing import Any, Literal, Optional
+from pydantic import BaseModel, BeforeValidator, Field
+from typing import Annotated, Any, Literal, Optional
 
 ClientMode = Literal["direct", "browser_addon"]
 
+
+def normalize_client_mode(value: Any) -> Any:
+    if value is None or (isinstance(value, str) and value.strip() == ""):
+        return "direct"
+    return value
+
+
+NormalizedClientMode = Annotated[ClientMode, BeforeValidator(normalize_client_mode)]
+
 class ProcessRequest_chat(BaseModel):
     sessionId: str = Field(..., max_length=64)
     timeStamp: str = Field(..., max_length=32)
     text: str = Field(...)
-    clientMode: ClientMode = "direct"
+    clientMode: NormalizedClientMode = "direct"
     needFormUpdate: bool = False
     useTextChunk: bool = False