How to make the title field of a node/add form hidden or locked
I'd probably just hide it with CSS to be honest.
Either that, or I'd use Automatic Nodetitles to populate the title with tokens (path token in your case) as it has the option to hide the title field AND auto-generate it with minimal effort.

&quot;auto_nodetitle&quot; is a small and efficient module that allows hiding of
the content title field in the form. To prevent empty content title
fields one can configure it to generate the title by a given pattern.
When the token module is installed it's possible to use various node
data for the auto generated title - e.g. use the text of a CCK field
(since 5.x).

Another option would be to use hook_form_alter() and set #disabled to TRUE to disable user input.