Don't allow duplicate endpoint to be submitted

[Ben-Hodgkiss]

Background

When an LPA submits an endpoint URL that is already active for that provision, they currently have no clear indication that their endpoint is being collected via the pipeline every night. This can cause them to resubmit, thinking they need to do that when they complete some of the tasks - creating unnecessary tickets.

Proposed solution

When an LPA checks an endpoint URL that already exists as an active endpoint for that provision in the system, the Check tool should:

• Still show the Check Results page as normal (do not block the check itself)
• Prevent the LPA from submitting again via the submit action
• Instead, the next steps page should display clear, reassuring content explaining that the dataset is already in the system, updates will be collected automatically overnight, and any task list issues will be resolved without needing to resubmit

Acceptance Criteria

• If the submitted endpoint URL matches an existing active endpoint for the same provision, the submit button/action is disabled or hidden
• A clear message is shown on the Check Results page explaining the dataset is already live
• The message communicates that the pipeline will automatically pick up any updates from the same URL
• The LPA is not left on a dead end - the message provides appropriate next steps or reassurance
• Existing flows for new (non-duplicate) endpoint submissions are unaffected
• If an active endpoint URL is submitted for a different dataset (or organisation), the LPA can still submit this (e.g. combined datasets)