Nutrient
fun NutrientToolbarItemButton(item: ToolbarItem, onAction: (ToolbarAction) -> Unit, modifier: Modifier = Modifier)
The render leaf for a single ToolbarItem — the smallest visual toolbar primitive.
Reuses the rest of the Phase 0 spine: colors from UiTheme / MainToolbarColors (#10), the accessibility contract from toolbarItemSemantics (#3), and the ToolbarIcon sealed type for rendering. A tap emits a ToolbarAction via onAction; the leaf holds no business logic.