[chubes4]

Part of Automattic/static-site-importer#2071.

Problem

Hosted builders often keep a native submit for semantics but move it off-screen with inline styles (position:absolute; left:-9999px; width:1px; height:1px) and paint a captioned sibling in its place (an <a class="…button">Send</a> with no href). The form layout and presentation graphs described the native control, so providers reproduced a 1px off-screen input and the visible submit disappeared after materialization.

Change

• FormControlClassifier::presentingElement() resolves the element that paints a native submit: an input/button submit moved off-screen by its inline style whose single adjacent non-control, non-navigating sibling carries the same caption. Ambiguous or captionless matches keep the native control.
• presentedControlElements() maps the shared control enumeration through it index for index, so control-N ids stay aligned with the control manifest.
• FormLayoutGraphBuilder and FormPresentationGraphBuilder describe presented elements. Control semantics (topology, classification, provider mapping) still read controlElements().
• A presenter carries its caption typography like a <button> does.
• CssValueInspector::isMovedOffscreenBox() uses the same 999px off-screen threshold hidesText() applies to text-indent.

Evidence

• New tests/unit/form-offscreen-submit-presenter.php (16 assertions) fails on trunk and passes here. It covers visible, clip-only, mismatched caption, ambiguous, navigating link, and non-submit negatives.
• Lab import of the hosted-builder contact page (2 pages, SSI main + this branch): the submit now renders with source paint (#f5a623, #fff, Montserrat 700) at 390/768/1440; on trunk it rendered no visible submit. Quality pass, 0 fallbacks.
• The remaining feat(release): configure native component releases #2071 gaps (caption box padding/transform, float pair row, block-flow stacking) are separate follow-ups.

AI disclosure: implemented with Claude (Pi backend via Roadie); Claude diagnosed the producer entity, wrote the change and test, and ran the Lab verification.