Understanding URL Behavior After New Action Validation Errors and Accompanying Errors

This is my first time to ask a question.I have a long question, but I will chew it up as much as possible, so I would appreciate it if you could let me know the details.

In my environment, when I post a new post with Rails, and when I get stuck in validation, the URL changes as follows:

ttp://localhost:3000/posts/new
↓↓↓
ttp://localhost:3000/posts

It may not be necessary, but this is what the controller expects.

def new
  @post=Post.new
  @post.build
end

def create
  @post=current_user.posts.build(post_params)
  [email protected]
    redirect_to post_path, notice: 'Post was successfully created.'
  else
    render action: : new
  end
end

I'm concerned about the URL, but when I get stuck in the validation, the contents of the form are kept, so I don't think it's a problem as long as I don't care about the URL.

However, if you return once with the browser button (ttp://localhost:3000/posts/new) and proceed again (ttp://localhost:3000/posts), the index action will be loaded as per the URL, so your entries will disappear.

If the index action is not configured, the following error occurs:

PostsController#index is missing a template for this request format and > variant.request.format: ["text/html"] request.variant: [ ] NOTE!For>XHR/Ajax or API requests, this action would normally respond with 204>Content.

If you write the index action on the controller as follows, the form will appear, but the contents of the form will disappear and I feel that it is aggressive.

def index
  @post=Post.new
  @post.build
  render action: : new
end

How do Rails users handle themselves?

The smart solution is
·Do not change the URL even after validation error (remain /post/new)
I think that's the quickest thing to do, but I don't know how to do it, and as long as Rails has changed the URL after the validation error, I think there's a reason (I don't know if I google it).

I would appreciate it if anyone could tell me the solution and how they usually deal with it.

I'm sorry for the amateur question.
Thank you for your cooperation.