Question about how Convex makes transactions in a mutation

import { mutation } from "@/convex/_generated/server";
import { v } from "convex/values";
import { GenericMutationCtx } from "convex/server";
import { api } from "@/convex/_generated/api";
import {
  getOrCreateGlobalDomain,
  getOrCreateGlobalUrl,
  getOrCreateUserObjectDomain,
  getOrCreateUserObjectUrl,
} from "@/utils/convex-query-helpers";

export const uploadHistoryItemMutation = mutation({
  args: {
    url: v.string(),
    domainUrl: v.string(),
  },
  handler: async (ctx, args) => {
    // Check if user is authenticated
    const identity = await ctx.auth.getUserIdentity();
    if (!identity) {
      throw new Error("User must be authenticated to create a history item");
    }

    const userId = identity.subject;
    const { url, domainUrl } = args;

    // Get or create all required entities using helper functions
    const globalDomainId = await getOrCreateGlobalDomain(ctx, domainUrl);
    const globalUrlId = await getOrCreateGlobalUrl(ctx, url, globalDomainId);
    const userObjectDomainId = await getOrCreateUserObjectDomain(
      ctx,
      userId,
      globalDomainId
    );
    const userObjectUrlId = await getOrCreateUserObjectUrl(
      ctx,
      userId,
      globalUrlId,
      globalDomainId,
      userObjectDomainId
    );

    // Create the history item
    const historyItemId = await ctx.db.insert("historyItems", {
      url,
      globalDomainId,
      globalUrlId,
      userObjectUrlId,
      userObjectDomainId,
      userId,
    });

    return {
      historyItemId,
      globalDomainId,
      globalUrlId,
    };
  },
});