The resolution gate on the pull-request, walkthrough, and mobile changes
surfaces stayed on forever (rootIsGitRepo stays false on a non-repo
root) while NestedRepoResolutionStates exits once the selected
repository probes as a repository, so those surfaces rendered nothing.
The gate now shows resolution states only while the operating directory
has not proven to be a repository, matching GitView.
Extract GitHeader's repository switcher into git/NestedRepoPicker and
mount it in the diff toolbar, a new slim header in the pull-request
view, the walkthrough header, and the mobile changes header. The pick
is shared per root, so every surface follows.
The walkthrough tab mounts keep-alive and hidden; it now receives a
visible prop so discovery waits until the tab is actually opened. Add
component tests for the shared resolution states.