Backing fields

For developers reading component data directly: every control on the toolbar writes one of these SDC props, all per-viewport unless noted:

Control	Backing field(s)
Width	container_type (narrow / contained / full / breakout); not per viewport
Height	height (auto / full / min / custom) and height_value (a CSS length, min/custom only); not per viewport
Layout → Structure	layout_type, count / count_auto, layout, min_item_width
Layout → Arrange → Vertical align / Stretch	valign (Columns) or grid_valign (Grid) — Stretch is valign: stretch, not a separate field
Layout → Arrange → Horizontal align	halign (Columns only), written only as start/center/end from this control
Layout → Arrange → Horizontal align (Grid)	grid_halign — a single unchanged Stretch/Start/Center/End row; it has no between/evenly values, so Grid has no Distribution row
Layout → Arrange → Column order	reverse
Layout → Spacing → Gap	gap (none / sm / md / lg / xl, 0 / 8 / 16 / 32 / 48px)
Layout → Spacing → Distribution	halign (Columns only) — the same field as Horizontal align above, written only as between/evenly from this control
Section settings	tag, section_id, section_classes, and the four hide_at_{viewport} booleans