Tighten up form transport stuff #16321

Describe the problem

It's a bug that you can manually specify the name of a remote form input:

<form {...myform}>
  <!-- good -->
  <input {...myform.fields.message.as('text')} />

  <!-- bad -->
  <input name="message" />

  <button>submit</button>
</form>

It's bad because it defeats type safety, and because it allows you to accidentally use a field from the wrong form, and because people will come to do weird shit that will break if we're forced to change some detail of the implementation at a later date.

Describe the proposed solution

Enforce the correct use of remote form fields by prefixing the name with an identifier, so that this...

<input {...myform.fields.message.as('text')} />

...renders as something like this:

<input type="text" name="xyz123/myform/s/message" value="..." aria-invalid="..." />

(I don't think we should include the id of a .for(...) in the prefix, that would be annoying.)

Alternatives considered

No response

Importance

nice to have

Additional Information

No response