Add technical guide for JULES visibility change (#623)

Co-authored-by: James Bruten <109733895+james-bruten-mo@users.noreply.github.com>

Author: Pierre-siddall

source/FurtherDetails/change_notes.rst

@@ -8,3 +8,5 @@
 
 Recent Changes
 ==============
+
+01/05/26 - Advice on for JULES being switched to `public visibility <visibility_changes.html>`_

source/FurtherDetails/index.rst

@@ -22,4 +22,5 @@ Further Details
     dos_donts
     fortitude_linter
     change_notes
+    visibility_changes
     coding_style

source/FurtherDetails/visibility_changes.rst

@@ -0,0 +1,62 @@
+.. -----------------------------------------------------------------------------
+    (c) Crown copyright Met Office. All rights reserved.
+    The file LICENCE, distributed with this code, contains details of the terms
+    under which the code may be used.
+   -----------------------------------------------------------------------------
+
+.. _visibility_changes:
+
+Changing Fork Visibility
+========================
+
+Technical Guide: Re-linking to a Public Repository
+--------------------------------------------------
+
+Once the repository is public, contributors must re-establish their forks to continue submitting pull requests.
+
+#. Create a new public fork (you will need to delete or rename existing private fork)**
+    1. Navigate to the now public repository
+    2. Click the Fork button int the top-right corner to create a new fork under your account
+
+#. Update Local Remotes
+    In your existing local clone, you must update your remote URLs to point to
+    the new public upstream and your new fork. Use the following commands:
+
+    .. code-block:: sh
+
+        # 1. Update the 'upstream' remote to point to the new public repository
+        git remote set-url upstream git@github.com:MetOffice/<repo>
+        # 2. Update your 'origin' remote to point to your NEW public fork
+        git remote set-url origin git@github.com:<user>/<repo>
+        # 3. Verify the changes
+        git remote -v
+
+#. Migrating unfinished work
+    As existing PRs will be closed or disconnected,
+    you will need to re-submit any open PRs from your new public fork.
+
+    The "detached" state is a security feature to isolate private forks when the
+    upstream parent becomes public. Only GitHub staff have the administrative
+    privileges required to manually re-link the repository network while
+    preserving existing PR data and history.
+
+    One option is to make sure any work you wish to preserve is in a clone of your
+    fork. Then recreate the fork from upstream using the same name as before.
+    Pushing from your clone will connect to the new fork. However this will delete
+    any pull requests you had open from the previous fork.
+
+**Note:** If you already have a lots of develop branches/PRs, its probably best to
+contact `GitHub Support and Submit a ticket
+<https://support.github.com/contact?legacy&subject=Attach%20Fork&tags=rr-forks>`_
+to reattach your fork. Select your personal account from the drop down menu
+(as that is where your fork is, not the enterprise account) and use the
+following message:
+
+  My upstream private repo became public, which detached my fork. I have open
+  PRs I need to preserve. Please reattach my fork to the original network.
+
+  Upstream URL: https://github.com/MetOffice/{repo-name}
+
+  Fork URL: https://github.com/{user}/{repo-name}
+
+This process should usually get resolved within a day.

source/git_faq.rst

@@ -50,31 +50,8 @@ repositories public. We have a copy of the repository with all the previous
 releases internal to the MetOffice. Please ask if you need help accessing
 that.
 
-.. rubric:: My forked repository got detached from upstream repository following
-  visibility change (private to public) upstream.
+.. rubric:: My forked repository got detached from upstream following a visibility change
 
-The "detached" state is a security feature to isolate private forks when the
-upstream parent becomes public. Only GitHub staff have the administrative
-privileges required to manually re-link the repository network while
-preserving existing PR data and history.
-
-One option is to make sure any work you wish to preserve is in a clone of your
-fork. Then recreate the fork from upstream using the same name as before.
-Pushing from your clone will connect to the new fork. However this will delete
-any pull requests you had open from the previous fork.
-
-If you already have a lots of develop branches/PRs, its probably best to
-contact `GitHub Support and Submit a ticket
-<https://support.github.com/contact?legacy&subject=Attach%20Fork&tags=rr-forks>`_
-to reattach your fork. Select your personal account from the drop down menu
-(as that is where your fork is, not the enterprise account) and use the
-following message:
-
-  My upstream private repo became public, which detached my fork. I have open
-  PRs I need to preserve. Please reattach my fork to the original network.
-
-  Upstream URL: https://github.com/MetOffice/{repo-name}
-
-  Fork URL: https://github.com/{user}/{repo-name}
-
-This process should usually get resolved within a day.
+For further details on how to migrate a detached fork after an upstream
+repository changes from private to public, see the :ref:`visibility_changes`
+guide.