Tab Lifecycle Marks

Agent-created tabs persist in the current ZCode process until the model explicitly calls tab.close(), the user closes the tab/window, or the process exits. Claimed user tabs return to the user when released.
tab.markDeliverable() keeps a user-facing result visible and releases it from browser control at turn cleanup.
tab.markHandoff() keeps unfinished work visible and controllable by this session in a later turn.
browser.tabs.finalize({ keep }) changes only the tabs listed in keep. Unlisted active/handoff tabs stay open; absence from keep is never an implicit close request.
turnEnded cancels pending requests and releases explicit deliverables or unmarked claimed user tabs, but it never closes a tab; an explicit handoff remains controlled. closeSession releases surviving tabs back to the owning conversation without closing their views. Released tabs never become visible to a different conversation.
browser.user.openTabs() only returns the current conversation's non-empty user tabs. Empty URLs and exact about:blank placeholders are intentionally omitted.
Closing every visible in-app browser tab in the current conversation requires both sources: close controlled tabs from browser.tabs.list(), then claim and close user tabs returned by browser.user.openTabs(). Other conversations remain inaccessible.