fix: allow blocked chat import drafts while keeping execution validation strict

backend/wisegrade/api.py

@@ -3,7 +3,7 @@ from pathlib import Path
 
 from fastapi import APIRouter, Depends, HTTPException
 from fastapi.responses import FileResponse
-from pydantic import BaseModel, Field, field_validator, model_validator
+from pydantic import BaseModel, Field, ValidationInfo, field_validator, model_validator
 from sqlalchemy import func, select
 from sqlalchemy.orm import Session
 
@@ -79,9 +79,13 @@ class ProjectConfirm(BaseModel):
         return value.strip() if isinstance(value, str) else value
 
     @model_validator(mode="after")
-    def validate_selection(self):
+    def validate_selection(self, info: ValidationInfo):
         selected = [file for file in self.files if file.status != "ignored"]
         if not selected:
+            # Only the chat preview builder supplies this context. HTTP imports,
+            # edited previews and final execution always use strict validation.
+            if (info.context or {}).get("allow_unselected_import_draft"):
+                return self
             raise ValueError("至少选择1份资料")
         categories = [file.category for file in selected]
         if any(category not in CATEGORIES for category in categories):