The agent's browser.open used to force the context panel open and steal
the active surface, which read as panels opening by themselves. Tab
upserts now take a reveal option: the agent's opener passes reveal: false,
so the tab mounts invisibly (panes are kept alive regardless of
visibility, so agent control still works) while the panel and the active
tab stay exactly as the user left them. Manual opens are unchanged.
Bohdan Triapitsyn
6770bc3717