diff --git a/backend/tests/test_chat_agent.py b/backend/tests/test_chat_agent.py
index c720c7b..cfadc73 100644
--- a/backend/tests/test_chat_agent.py
+++ b/backend/tests/test_chat_agent.py
@@ -214,6 +214,12 @@ def test_duplicate_scan_requires_teacher_file_choice(environment, db):
     generated_action = db.get(PendingAction, generated["pending_action"]["id"])
     assert generated_action.preview["requires_edit"] is True
     assert all(file["status"] == "ignored" for file in generated_action.payload["projects"][0]["files"])
+    with pytest.raises(HTTPException) as blocked:
+        confirm(db, conversation, generated_action.id)
+    assert blocked.value.status_code == 409
+    with pytest.raises(HTTPException) as invalid_selection:
+        prepare(db, conversation, "import", generated_action.payload, teacher_edited=True)
+    assert invalid_selection.value.status_code == 400
     proposed = prepare(db, conversation, "import", payload)
     assert proposed.preview["requires_edit"] is True
     with pytest.raises(HTTPException):
diff --git a/backend/wisegrade/actions.py b/backend/wisegrade/actions.py
index bd46d95..c8542b9 100644
--- a/backend/wisegrade/actions.py
+++ b/backend/wisegrade/actions.py
@@ -6,6 +6,7 @@ from pathlib import Path
 from uuid import uuid4
 
 from fastapi import HTTPException
+from pydantic import ValidationError
 from sqlalchemy import select
 
 from . import services
@@ -149,7 +150,12 @@ def prepare(db, conversation: Conversation, kind: str, payload: dict, *, teacher
         raise HTTPException(400, "整批 Excel 导出须在未限定学生项目的会话中准备")
     if kind == "import":
         from .api import ImportConfirm
-        data = ImportConfirm.model_validate(payload)
+        try:
+            data = ImportConfirm.model_validate(payload, context={
+                "allow_unselected_import_draft": not teacher_edited})
+        except ValidationError as exc:
+            messages = [error["msg"] for error in exc.errors(include_input=False, include_context=False)]
+            raise HTTPException(400, "导入资料尚未满足确认条件：" + "；".join(messages)) from exc
         payload = data.model_dump()
         require_scope(db, conversation, version_id=data.course_version_id)
         if teacher_edited and any(item.student_no == "00000" or item.name == "待确认" or item.topic == "待确认" for item in data.projects):
@@ -164,9 +170,10 @@ def prepare(db, conversation: Conversation, kind: str, payload: dict, *, teacher
             scanned.append(match)
             if match["status"] != "recognized" or match["warnings"] or any(f["status"] != "recognized" for f in match["files"]):
                 ambiguous.append(item.relative_dir)
+        unselected = any(not any(file.status != "ignored" for file in item.files) for item in data.projects)
         preview = {"course_version_id": data.course_version_id, "projects": scanned,
                    "selection": payload["projects"], "ambiguous": ambiguous,
-                   "requires_edit": bool(ambiguous) and not teacher_edited}
+                   "requires_edit": (bool(ambiguous) or unselected) and not teacher_edited}
     elif kind == "course_ingest":
         require_scope(db, conversation, version_id=payload["course_version_id"])
         preview = {"course_version_id": payload["course_version_id"], "templates":
diff --git a/backend/wisegrade/api.py b/backend/wisegrade/api.py
index 0a23666..7341ba2 100644
--- a/backend/wisegrade/api.py
+++ b/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):