Add SCROLL

[brynary]

Stacked on #25. The last of three pointer-action PRs: scrolling, as a flow command and as ACT methods. It also closes the SPEC §18 item for more ACT methods.

Change

Form	Meaning
SCROLL locator	Bring the element into view.
SCROLL [locator] down / up / left / right	Scroll one visible height or width.
SCROLL [locator] to 50%	Scroll to a vertical position. A new percent literal, 0% to 100%.

• Which box scrolls. The element when it can scroll in that direction, else the largest box inside it that can, else its nearest ancestor that can, else its document. An iframe element scrolls the page inside it, across origins too. html and body stand for the page, and no locator means the page. So SCROLL text:"Filter 3" down and SCROLL role:dialog Filters down both scroll the dialog's list.
• How. The shim sets the position at once, even when the page asks for smooth scrolling, and the step ends when the position holds for two frames. A box already there stays put, and the step passes. scroll events and intersection observers fire; wheel events do not.
• Syntax. A trailing bare down, up, left, or right and a bare to are keywords. whirl fmt keeps the quotes on text that spells them, such as SCROLL "down".
• ACT. scrollIntoView, scrollTo, nextChunk, prevChunk, scrollLeft, and scrollRight. In a whole-page snapshot the first element is <body> in all three engines, so a scroll of it runs and reports as the page form, SCROLL down. scrollTo needs a percent; anything else fails with act-invalid-decision. With --jev, scrolls go to the model.
• Limit. A row that a virtualized list has not rendered cannot be scrolled into view. The SPEC says to write enough SCROLL locator down lines first.

Evals

Five models, the six new tasks (this PR and #24, #25), three runs each. Summary: evals/act/results/2026-09-27-local.md.

task	terra	luna	flash-lite	jev + flash-lite	jev + luna
right-click-menu	3/3	3/3	3/3	3/3	3/3
kanban-move	3/3	3/3	3/3	3/3	3/3
scroll-halfway	3/3	3/3	3/3	3/3	3/3
scroll-back-up	3/3	3/3	3/3	3/3	3/3
scroll-panel-chunk	3/3	3/3	3/3	3/3	3/3
scroll-in-frame	3/3	3/3	3/3	3/3	3/3

The first run, before commit 0a9f2d2, passed 0.67 to 0.94. Models answer "scroll down one chunk in the filters panel" with the dialog, and "scroll inside the incident history" with the iframe element; neither can scroll, so the page behind the dialog scrolled and the frame did not. 0a9f2d2 looks inside the named element and enters an iframe. The rerun still names the dialog in 12 of 15 runs and the iframe in 10 of 15, and all pass. With --jev, Jev plans every right click; drags and scrolls go to the model. Both sessions cost about $0.09.

Tests

• Browser, in all three engines: a dialog's list scrolled through the dialog; a same-origin and a cross-origin frame scrolled through their iframe elements; one chunk equals the viewport height; to 100% triggers a lazy load and shows a back-to-top button; to 0%; a trigger scrolled into view loads more; a chunk inside a dialog panel found by its text; to 100% on a terms box enables "I agree", and one more chunk passes without moving; a sideways board; SCROLL "down" as text; and a scrollable iframe that scrolls while the page stays put.
• ACT: the page's <body> renders as SCROLL to 100%; a position that is not a percent fails; a --jev scroll goes to the model.
• Unit: parsing, percent literals, fmt quoting, the six methods, and the prompt.
• Eval: scroll-halfway, scroll-panel-chunk, scroll-back-up, and scroll-in-frame, each checked first with plain SCROLL lines.
• mise run check passes. SPEC §3.1, §6.1, §7, §7.4, §17, and §18, the shim protocol doc, and the CHANGELOG describe the change.

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