Off should mean the model is never told the tool exists. A switch that
only made the call fail leaves Hermes offering walkthroughs it cannot
give and promising to point at things it cannot point at, which reads as
a broken agent rather than a respected preference.
Both gate on the switch through a shared desktop_ui.user_enabled helper,
which is the reactions check_fn generalized — same config read, same
reason it has to be config rather than an env var: the switch belongs to
the session's client, and the client may be on another machine.
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