### Problem/Motivation Council webforms need a reference number residents can quote and staff can search on. Webform's `serial`/UUID aren't configurable or recognisable, and there's no built-in way to show such a value in confirmations, emails, or the submission view. This is baseline functionality for LocalGov form sites, so it belongs in `localgov_forms`. This contribs a feature running in production on Walsall Council's site. ### Proposed resolution Add an opt-in, per webform reference number: - "Reference number" group on each webform's General settings: an enable toggle and a token-pattern `format` (default `[webform:id]-[webform_submission:serial]`). - Generated on submission insert and stored in submission data. - Exposed as token `[webform_submission:localgov_forms_reference]` (for emails / confirmations) and shown on the admin submission view as a pseudo-field. Adds a `token` dependency. Includes config schema and Kernel tests (D10 + D11).