fix(syncedinstance): Prevent same-instance syncs and sanitize post update payloads; update tests and docs

ts/classes.post.ts

@@ -118,9 +118,34 @@ export class Post {
     return this.postData;
   }
 
-  public async update(postData: IPost): Promise<Post> {
+  public async update(postData: Partial<IPost>): Promise<Post> {
     try {
-      const updatedPostData = await this.ghostInstanceRef.adminApi.posts.edit(postData);
+      // Only send fields that should be updated, not the entire post object with nested relations
+      const updatePayload: any = {
+        id: this.postData.id,
+        updated_at: this.postData.updated_at, // Required for conflict detection
+        ...postData
+      };
+
+      // Remove read-only or computed fields that shouldn't be sent
+      delete updatePayload.uuid;
+      delete updatePayload.comment_id;
+      delete updatePayload.url;
+      delete updatePayload.excerpt;
+      delete updatePayload.reading_time;
+      delete updatePayload.created_at; // Don't send created_at in updates
+      delete updatePayload.primary_author;
+      delete updatePayload.primary_tag;
+      delete updatePayload.count;
+      delete updatePayload.email;
+      delete updatePayload.newsletter;
+
+      // Remove nested objects if they're not being updated
+      if (!postData.authors) delete updatePayload.authors;
+      if (!postData.tags) delete updatePayload.tags;
+      if (!postData.tiers) delete updatePayload.tiers;
+
+      const updatedPostData = await this.ghostInstanceRef.adminApi.posts.edit(updatePayload);
       this.postData = updatedPostData;
       return this;
     } catch (error) {