fix: validate retrieval-only chat questions before dispatch

backend/app/schemas/chat.py

@@ -1,11 +1,14 @@
 from typing import Literal
 from uuid import UUID
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel
+
+from app.schemas.catalog import Input
+from app.schemas.retrieval import QueryText
 
 
-class ChatRequest(BaseModel):
-    question: str = Field(min_length=1, max_length=2000)
+class ChatRequest(Input):
+    question: QueryText
 
 
 class SourcePreview(BaseModel):

backend/app/schemas/retrieval.py

@@ -1,14 +1,16 @@
 from datetime import datetime
-from typing import Literal
+from typing import Annotated, Literal
 from uuid import UUID
 
 from pydantic import BaseModel, Field
 
 from app.schemas.catalog import Category, Input
 
+QueryText = Annotated[str, Field(min_length=1, max_length=500)]
+
 
 class RetrievalRequest(Input):
-    query: str = Field(min_length=1, max_length=500)
+    query: QueryText
     mode: Literal["keyword"] = "keyword"
     top_k: int = Field(default=5, ge=1, le=20)
     category: Category | None = None