fix(layout): retain normal grid stretching for native form controls

Map native controls to compressible replaced leaves without the image-only replaced flag. Cover checkbox, radio and range normal alignment at 50 by 50 pixels.

Validation: cargo fmt --all; cargo clippy --workspace --all-targets --all-features -- -D warnings; cargo nextest run --no-fail-fast (20283 passed, 18 skipped). Release v3 and five browser regression rounds. Full WPT recorded separately.

moli-layout/src/builder.rs

@@ -138,7 +138,9 @@ where
             root_style.force_display_none();
         }
         if root_semantics.is_replaced() {
-            root_style.mark_replaced();
+            root_style.mark_replaced(
+                root_semantics.replaced == Some(crate::LayoutReplacedKind::FormControl),
+            );
         } else if matches!(
             root_semantics.category,
             crate::LayoutElementCategory::FormControl(crate::LayoutFormControlKind::Button)
@@ -306,7 +308,9 @@ where
             }
             let metrics = self.source.replaced_metrics(source_node);
             if semantics.is_replaced() {
-                style.mark_replaced();
+                style.mark_replaced(
+                    semantics.replaced == Some(crate::LayoutReplacedKind::FormControl),
+                );
             } else if matches!(
                 semantics.category,
                 crate::LayoutElementCategory::FormControl(crate::LayoutFormControlKind::Button)

moli-layout/src/style.rs

@@ -2121,8 +2121,11 @@ impl ResolvedLayoutStyle {
         }
     }
 
-    pub(crate) fn mark_replaced(&mut self) {
-        self.taffy.item_is_replaced = true;
+    pub(crate) fn mark_replaced(&mut self, is_form_control: bool) {
+        // Taffy distinguishes native controls from images for normal grid/OOF
+        // stretch. Both remain compressible replaced leaves in block layout.
+        self.taffy.item_is_replaced = !is_form_control;
+        self.taffy.item_is_compressible_replaced = is_form_control;
     }
 
     pub(crate) fn resolved_aspect_ratio(

moli-layout/tests/main_layout_contract.rs

@@ -709,6 +709,53 @@ fn grid_item_placement_and_self_alignment_use_the_selected_grid_area() {
     );
 }
 
+#[test]
+fn native_form_controls_stretch_under_normal_grid_alignment() {
+    use moli_layout::{LayoutFormControlKind, LayoutInputControlKind};
+    for kind in [
+        LayoutInputControlKind::Checkbox,
+        LayoutInputControlKind::Radio,
+        LayoutInputControlKind::Range,
+    ] {
+        let mut control = FixtureNode::html("control", "input", Vec::new());
+        control.semantics = LayoutElementSemantics::new(
+            LayoutNamespace::Html,
+            "input",
+            LayoutElementCategory::FormControl(LayoutFormControlKind::Input(kind)),
+            Some(LayoutReplacedKind::FormControl),
+        );
+        let source = FixtureSource {
+            nodes: vec![FixtureNode::div("grid", vec![1]), control],
+        };
+        let mut styles = FixtureStyles::default();
+        styles.0.insert(
+            0,
+            resolved(
+                LayoutDisplay::Grid,
+                Style {
+                    display: Display::Grid,
+                    size: Size {
+                        width: length(50.0),
+                        height: length(50.0),
+                    },
+                    grid_template_columns: vec![length(50.0)],
+                    grid_template_rows: vec![length(50.0)],
+                    ..Style::default()
+                },
+                PaintColor::TRANSPARENT,
+            ),
+        );
+        styles
+            .0
+            .insert(1, resolved(LayoutDisplay::Block, Style::default(), RED));
+        let snapshot = render(&source, &mut styles, PaintViewport::new(100, 100, 1.0));
+        assert_rect(
+            solid_rect(&snapshot, RED),
+            PaintRect::new(0.0, 0.0, 50.0, 50.0),
+        );
+    }
+}
+
 #[test]
 fn absolute_grid_items_use_retained_track_areas_in_both_directions() {
     for (direction, x) in [