The pane, in-app browser, and reaction tools were gated on HERMES_DESKTOP=1 —
an env var set only on backends Electron spawns itself (local and SSH). A
desktop client connected to a plain URL gateway or Hermes Cloud lost all six:
they were stripped from the schema before the model saw them, on the same
backend whose platform hint was telling it "you are chatting inside the Hermes
desktop app". open_preview, read_preview, read_terminal, close_terminal,
focus_pane, and react_to_message were all silently absent.
The client is not the host. Capability now resolves from the session's own
source, which session.create already carries:
- The six tools move into a `desktop_ui` toolset, off _HERMES_CORE_TOOLS so no
other platform pays their schema.
- _gui_surface_toolsets(platform) folds `desktop_ui` (and the existing
`project` tools) into the GUI gateway's resolution when the session's
platform is the desktop app — the same answer on every topology.
- check_fn drops the env probe. It kept the one thing that is genuinely a
per-process/user fact: react_to_message's display.message_reactions opt-in,
which the desktop mirrors onto whichever gateway it is connected to.
react_to_message was doubly broken: it read that toggle behind the env gate, so
even a local-backend user's Settings toggle could not reach a remote session.
The embedded terminal pane keeps working correctly the other way round: it runs
`hermes --tui` against a desktop-spawned backend, and a tui-sourced session
gets no GUI tools even though HERMES_DESKTOP=1 is set on that process.
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