An inline ::preview widget could render and be clicked, but the click went
nowhere: the sandbox has no channel to the agent, so an interactive chart
was a dead end. Now the frame injects a second script beside the measurer
that gives the page one voice:
window.hermes.send('get-price eth')
<button data-hermes-send="get-price eth">ETH</button> (zero-script form)
The prompt rides postMessage up tagged with the mount token, then goes
through the composer's own send path (requestComposerSubmit -> prompt.submit)
flagged display_kind=hidden — the same row-typing auto-continue and internal
notifications already use. The agent wakes and takes a real turn; the
durable row persists (context, resume, DB audit); but NO bubble renders,
live or on reload. The user clicks ETH and the chart just changes — the
off-screen loop is click -> hidden turn -> agent rewrites the widget file ->
frame hot-swaps.
Trust boundary matches size reports and is tighter where it matters: mount
token required (frames can't forge each other's intents), string-only,
trimmed, capped at 500 chars, throttled to one intent per second per frame.
The gateway whitelists display_kind to "hidden" — the RPC can't mint
arbitrary row types — and the flag threads through both turn paths (inline
and compute-host isolation) so isolated sessions don't resurrect bubbles on
resume.
The desktop platform hint teaches the model to wire interactive widgets
with data-hermes-send and to answer clicks by updating the widget's file
rather than with prose; the SDK doc documents the contract.
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