* diff: the session's start asks nothing of the repository; /diff or the first edit pins it when it comes
* diff: git runs when the built-in panel's would: one rev-parse at first need, the tree walked only for an open pane, nothing after a turn or a refused tool
* diff: a shell command that failed or was cut short still refreshes an open pane, an edit that did opens nothing, and a probe /clear overtook pins nothing