* feat(agent): read_preview — the desktop-gated tool that reads the in-app browser
The agent could open the preview pane (open_preview) and read the embedded
terminal (read_terminal), but the browser it had just opened was a black box —
'what does this page say?' had no answer. read_preview mirrors read_terminal
end to end: HERMES_DESKTOP-gated via check_fn (zero schema footprint outside
the GUI), dispatched through the same agent callback pattern, windowed with
start/count so a long page pages instead of flooding context.
* feat(gateway): preview.read blocking bridge
Same lifecycle as terminal.read: the tool blocks on preview.read.request, the
renderer answers preview.read.respond (allow_expired — a slow page extraction
losing the 45s race must not surface a raw 4009), and a timeout emits
preview.read.expire so late answers resolve quietly.
* feat(desktop): the renderer serializes the active preview tab for the agent
preview-reader.ts is the preview analog of the terminal's buffer registry: the
URL pane registers a page reader (webview executeJavaScript → title + visible
innerText) keyed by tab id; readActivePreview resolves the ACTIVE tab, windows
the text (24k cap per read), and answers file/artifact tabs with identity plus
a note pointing at the tool that reads that content directly. The gateway
event handler answers preview.read.request beside terminal.read.request.
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