图生 3D 的素材库空确认不再清掉已选参考图

- src/components/image-editor/ImageCanvasGenerationDialogModel.ts：单槽对话框只在素材库确实选到了图时才做「替换」，空确认退回原行为（保留画布点选/上传的那张）。此前确认按钮不校验空选，空确认会把已有参考图直接清掉
- src/components/image-editor/projectAssetReferencePickerModel.test.ts：补空确认保留画布参考图的用例

src/components/image-editor/ImageCanvasGenerationDialogModel.ts

@@ -2265,7 +2265,8 @@ export function replaceProjectAssetPickerReferences(
     ...resetFailedGenerationDialog(dialog),
     generationReferences: appendLimitedImageReferences(
       // 单槽对话框（图生 3D）里素材库选择是替换：留着画布点选的那张只会把这次选择挤掉。
-      usesSingleImageReferenceSlot(dialog)
+      // 但确认时一个都没选就不算「替换」，否则空确认会把画布点选/上传的那张直接清掉。
+      usesSingleImageReferenceSlot(dialog) && references.length > 0
         ? []
         : (dialog.generationReferences ?? []).filter(
             (reference) => !isProjectAssetPickerReference(reference),

src/components/image-editor/projectAssetReferencePickerModel.test.ts

@@ -272,6 +272,30 @@ describe('参考图弹窗素材筛选与快照', () => {
     expect(next).toMatchObject({ status: 'idle', composerOpen: true });
   });
 
+  it('keeps the 3D image-to-model source when the picker is confirmed empty', () => {
+    const dialog = {
+      mode: 'model3d-image-to-model',
+      prompt: '',
+      status: 'failed',
+      errorMessage: '失败',
+      composerOpen: false,
+      generationReferences: [
+        {
+          id: 'canvas-layer-1',
+          label: '画布点选',
+          src: 'https://example.test/canvas.png',
+          mediaType: 'image',
+        },
+      ],
+    } satisfies GenerateDialogState;
+
+    const next = replaceProjectAssetPickerReferences(dialog, []);
+
+    expect(
+      next?.generationReferences?.map((reference) => reference.id),
+    ).toEqual(['canvas-layer-1']);
+  });
+
   it('leaves dialogs outside the reference-composer modes untouched', () => {
     const dialog = {
       mode: 'video',