Every drive_preview action answered with the entire inventory — around 120
elements of ref, role, label, and an up-to-eight-rung `:nth-child` selector
chain. On a real app shell that was ~24.5k characters, re-sent after every
click, so a ten-step task paid for ten copies of a page that had barely moved.
Handles are now durable and legible. An element is named after what it is and
what it says — `btn-sign-in`, `inp-email`, `srch-search-projects` — minted once
per page and never reused, with duplicates disambiguated as `btn-edit`,
`btn-edit-1`. Each one remembers a stable attribute, its role, its accessible
name, and the nearest landmark it sits in, so when a framework destroys the
node and builds a new one the handle moves across and the agent is told
`rebound` rather than being handed a removal it has to react to and an addition
it has to re-read. The re-bind ladder is anchortree's (Apache-2.0), minus its
geometry rung, which can never clear the threshold on its own.
Because the handles hold, the first look at a page returns the inventory and
every look after it returns only what moved. `changed` carries the ref and
whichever of label/value/disabled actually shifted — role and selector are
absent by construction, since a change in either would mean the re-bind ladder
was looking at a different element. A delta gives way to a full re-read when
half the page is new, where there is nothing left to reuse.
The selector column is gone with it. It was 74% of the inventory on an
85-element page, nothing downstream ever read it, and a positional chain is
wrong the moment a sibling appears. An `#id` or `[data-testid]` survives when
the page offers one; everything else is addressed by handle.
Legibility is what makes the delta work rather than a nicety. `+ btn-sign-in`
on turn nine reads on its own, where `+ @e42` sends the model back to an
inventory twenty thousand tokens ago.
Measured on an 85-element app shell: 18,693 -> 4,930 characters for a baseline,
and a steady turn that moved two things costs ~200.
The in-app browser was a one-way mirror. open_preview put a page in the pane
and read_preview read its text back, but nothing could touch it. A click meant
falling back to the browser_* tools, which drive a separate Chromium the user
cannot see — so "log into this and pull my invoices" happened in a different
browser from the one on screen, with none of the sessions the user is already
signed into.
Four pieces, and they only make sense together:
· an in-page engine that inventories what is interactable and performs the
verb, injected as source because it has to run inside the guest page;
· the preview.act.request bridge from the gateway into the pane;
· drive_preview, for acting: elements, click, type, scroll, press, and the
pane's own back/forward/reload;
· annotate_preview, for marking without acting.
Those last two started as one tool doing two unrelated jobs. Leaving a mark is
not an action — it outlives the turn that drew it — so it gets its own verb,
and the interaction verb gets a name that says what it does.
Gating is the existing surface rule: desktop_ui folds in on session
source: 'desktop', and the bridge refuses to act for a background session, so a
turn running behind the user's back cannot reach into the page they are working
in.
Two details worth a reviewer's attention. Typing assigns through the
prototype's value setter, because React shadows value with its own accessor and
ignores an input event whose value it believes it already wrote — a plain
el.value = … types into a field that snaps back on the next render. And
clicking replays the pointer/mouse pair before activation, because frameworks
bind to mousedown as often as to click.
