The Desktop and TUI subcommand pickers offer /browser use (it is in the
registry's subcommands), but both handlers only knew connect, disconnect
and status, so picking it printed the usage line.
browser.manage gains a use action (enabled: bool) that writes the session
profile's browser.backend through the same set_browser_use_mode helper the
CLI now calls, and status/use report browser_use. The handler is profile
scoped, so a worker session writes its own profile. A live agent keeps its
tools (prompt cache), so Desktop and TUI say the switch applies to new
chats instead of swapping tools mid-conversation. use and status also run
on remote backends; connect/disconnect stay local-only.
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