The explorer companion pane retention commit (de9e85862) auto-opens the
setup progress tab into the hidden explorer pane. toggleWorkspaceExplorerPane
only seeded the working_diff (Changes) tab when the pane was completely
empty, so once the setup tab landed there, clicking the explorer toggle
could never surface Changes/Files again via that pane's default tab.
Also fixes two e2e testid locators (workspace-new-tab-menu-trigger) and
one unit test assertion (browser automation handler) that assumed a bare
pane root, which predates that same explorer-pane-retention change: the
workspace root is now always a group with a hidden companion pane, so
unscoped locators/assertions must target the visible/named pane.
Mohamed Boudra
bd3f3c7714