fix: paste synced doc (#8355)

Closes: [BS-381](https://linear.app/affine-design/issue/BS-381/%E5%B8%A6-embed-view-%E7%9A%84-note-%E5%A4%8D%E5%88%B6%E6%97%B6%EF%BC%8C%E5%8F%AA%E5%A4%8D%E5%88%B6%E4%BA%86-embed-%E7%9A%84%E9%83%A8%E5%88%86)

packages/blocks/src/_common/transformers/middlewares.ts

@@ -92,31 +92,22 @@ export const replaceIdMiddleware: JobMiddleware = ({ slots, collection }) => {
     // TODO(@fundon): process linked block/element
     if (
       payload.type === 'block' &&
-      payload.snapshot.flavour === 'affine:embed-linked-doc'
+      ['affine:embed-linked-doc', 'affine:embed-synced-doc'].includes(
+        payload.snapshot.flavour
+      )
     ) {
-      const model = payload.model as EmbedLinkedDocModel;
+      const model = payload.model as EmbedLinkedDocModel | EmbedSyncedDocModel;
       const original = model.pageId;
-      if (idMap.has(original)) {
-        model.pageId = idMap.get(original)!;
-      } else {
-        const newId = collection.idGenerator();
-        idMap.set(original, newId);
-        model.pageId = newId;
-      }
-    }
-
-    if (
-      payload.type === 'block' &&
-      payload.snapshot.flavour === 'affine:embed-synced-doc'
-    ) {
-      const model = payload.model as EmbedSyncedDocModel;
-      const original = model.pageId;
-      if (idMap.has(original)) {
-        model.pageId = idMap.get(original)!;
-      } else {
-        const newId = collection.idGenerator();
-        idMap.set(original, newId);
-        model.pageId = newId;
+      // If the pageId is not in the doc, generate a new id.
+      // If we already have a replacement, use it.
+      if (!collection.getDoc(original)) {
+        if (idMap.has(original)) {
+          model.pageId = idMap.get(original)!;
+        } else {
+          const newId = collection.idGenerator();
+          idMap.set(original, newId);
+          model.pageId = newId;
+        }
       }
     }
   });