Fix modern stylesheet and image geometry

crates/obscura-browser/src/page.rs

@@ -438,14 +438,76 @@ fn materialize_linked_stylesheet_script(link_index: usize, css: &str) -> String
             var links = document.querySelectorAll('link[rel~="stylesheet"]');
             var link = links[{link_index}];
             if (!link || !link.parentNode) return;
-            var style = document.createElement('style');
-            style.setAttribute('data-obscura-external-stylesheets', '');
-            style.textContent = `{escaped_css}`;
-            link.parentNode.insertBefore(style, link.nextSibling);
+            var style = null;
+            function effectiveMedia() {{
+                // Until the generic Element shim reflects HTMLLinkElement.media,
+                // `this.media = "all"` creates an own property while the parsed
+                // media="print" attribute remains unchanged.
+                if (Object.prototype.hasOwnProperty.call(link, 'media')) {{
+                    return String(link.media || '');
+                }}
+                return link.getAttribute('media') || '';
+            }}
+            function applies() {{
+                var media = effectiveMedia().trim();
+                if (!media) return true;
+                try {{ return window.matchMedia(media).matches; }}
+                catch (_) {{ return false; }}
+            }}
+            function syncSheet() {{
+                var enabled = link.parentNode
+                    && !link.disabled
+                    && !link.hasAttribute('disabled')
+                    && applies();
+                if (!enabled) {{
+                    if (style && style.parentNode) style.parentNode.removeChild(style);
+                    return;
+                }}
+                if (!style) {{
+                    style = document.createElement('style');
+                    style.setAttribute('data-obscura-external-stylesheets', '');
+                    style.textContent = `{escaped_css}`;
+                }}
+                if (!style.parentNode) {{
+                    link.parentNode.insertBefore(style, link.nextSibling);
+                }}
+            }}
+
+            // A non-matching sheet still loads and fires its event. Its handler
+            // may then make the sheet applicable (the common
+            // media=print/onload="this.media='all'" async-CSS pattern).
+            syncSheet();
+            try {{ link.dispatchEvent(new Event('load')); }}
+            finally {{ syncSheet(); }}
         }})()"#
     )
 }
 
+/// Discover linked author sheets in document order.
+///
+/// Media queries control whether a loaded sheet participates in the cascade;
+/// they do not suppress its fetch or `load` event. Keep the index among all
+/// stylesheet links so the materialization script addresses the same node.
+fn linked_stylesheet_requests(dom: &DomTree) -> Vec<(usize, String)> {
+    let link_ids = dom
+        .query_selector_all("link[rel~=\"stylesheet\"]")
+        .unwrap_or_default();
+    let mut links = Vec::new();
+    for (link_index, lid) in link_ids.into_iter().enumerate() {
+        if let Some(node) = dom.get_node(lid) {
+            // Disabled alternate sheets remain dormant until script enables
+            // them. Media-gated sheets are different: they still load.
+            if node.get_attribute("disabled").is_some() {
+                continue;
+            }
+            if let Some(href) = node.get_attribute("href") {
+                links.push((link_index, href.to_string()));
+            }
+        }
+    }
+    links
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 struct HydrationStats {
     elements: usize,
@@ -772,53 +834,7 @@ impl Page {
     
     async fn fetch_stylesheets(&mut self) {
         let all_links = match &self.js {
-            Some(js) => {
-                js.with_dom(|dom| {
-                    // `rel` is a space-separated token list. VitePress and
-                    // other modern generators combine preload and stylesheet
-                    // (`rel="preload stylesheet"`); exact-value matching
-                    // silently skipped their entire CSS payload.
-                    let link_ids = dom
-                        .query_selector_all("link[rel~=\"stylesheet\"]")
-                        .unwrap_or_default();
-                    let mut links = Vec::new();
-                    for (link_index, lid) in link_ids.into_iter().enumerate() {
-                        if let Some(node) = dom.get_node(lid) {
-                            // Skip disabled stylesheets: a `<link ... disabled>`
-                            // does not apply until JS clears the attribute. Sites
-                            // ship alternate themes this way (e.g. Google devsite's
-                            // dark-theme.css is linked `disabled` and toggled by a
-                            // theme switcher); applying it painted whole pages dark
-                            // when Chromium renders them light. `disabled` is a
-                            // boolean attribute, so any presence means off.
-                            if node.get_attribute("disabled").is_some() {
-                                continue;
-                            }
-                            // Respect the link's `media` gate. A `<link
-                            // media="print">` must not apply on screen (the
-                            // Guardian ships a print sheet that otherwise
-                            // overrode the screen masthead), and a `<link
-                            // media="(prefers-color-scheme: dark)">` must not
-                            // apply in our light desktop context (docs.python and
-                            // other Sphinx sites link pydoctheme_dark.css this way;
-                            // injecting it painted the page dark under a light
-                            // Chromium). We render the default light context, so
-                            // skip sheets gated to print-only or dark preference.
-                            if let Some(media) = node.get_attribute("media") {
-                                let compact: String = media.chars().filter(|c| !c.is_whitespace()).flat_map(|c| c.to_lowercase()).collect();
-                                let print_only = compact.contains("print") && !compact.contains("screen") && !compact.contains("all");
-                                if print_only || compact.contains("prefers-color-scheme:dark") {
-                                    continue;
-                                }
-                            }
-                            if let Some(href) = node.get_attribute("href") {
-                                links.push((link_index, href.to_string()));
-                            }
-                        }
-                    }
-                    links
-                }).unwrap_or_default()
-            }
+            Some(js) => js.with_dom(linked_stylesheet_requests).unwrap_or_default(),
             None => {
                 tracing::info!("fetch_stylesheets: no js runtime");
                 return;
@@ -2338,9 +2354,10 @@ fn url_matches_cdp_pattern(pattern: &str, url: &str) -> bool {
 #[cfg(test)]
 mod tests {
     use super::{
-        materialize_linked_stylesheet_script, parse_import_url, rebase_css_urls,
-        should_restore_hydration_snapshot, split_css_imports, script_response_is_executable,
-        truncate_on_char_boundary, url_matches_cdp_pattern, HydrationStats,
+        linked_stylesheet_requests, materialize_linked_stylesheet_script, parse_import_url,
+        rebase_css_urls, should_restore_hydration_snapshot, split_css_imports,
+        script_response_is_executable, truncate_on_char_boundary, url_matches_cdp_pattern,
+        HydrationStats,
     };
     use obscura_dom::parse_html;
 
@@ -2484,6 +2501,123 @@ mod tests {
         );
     }
 
+    #[test]
+    fn media_gated_stylesheets_are_fetched_but_disabled_sheets_are_not() {
+        let dom = parse_html(
+            r#"<link rel="stylesheet" href="screen.css">
+               <link rel="stylesheet" href="async.css" media="print"
+                     onload="this.media='all'">
+               <link rel="stylesheet" href="dark.css"
+                     media="(prefers-color-scheme: dark)">
+               <link rel="stylesheet" href="disabled.css" disabled>"#,
+        );
+
+        assert_eq!(
+            linked_stylesheet_requests(&dom),
+            vec![
+                (0, "screen.css".to_string()),
+                (1, "async.css".to_string()),
+                (2, "dark.css".to_string()),
+            ]
+        );
+    }
+
+    #[test]
+    fn print_media_onload_can_activate_a_fetched_stylesheet() {
+        let dom = parse_html(
+            r#"<html><head>
+                <link id="async" rel="stylesheet" href="async.css" media="print"
+                      onload="this.media='all';this.setAttribute('data-loaded','yes')">
+            </head><body></body></html>"#,
+        );
+        let mut runtime = obscura_js::runtime::ObscuraJsRuntime::new();
+        runtime.set_dom(dom);
+        runtime.run_page_init();
+        runtime
+            .execute_script(
+                "<async-sheet>",
+                &materialize_linked_stylesheet_script(0, ".target{color:red}"),
+            )
+            .expect("load and materialize async linked sheet");
+
+        let state = runtime
+            .with_dom(|dom| {
+                let link = dom
+                    .query_selector("#async")
+                    .expect("valid selector")
+                    .expect("async link");
+                let styles = dom
+                    .query_selector_all("style[data-obscura-external-stylesheets]")
+                    .expect("valid selector");
+                (
+                    dom.get_node(link)
+                        .and_then(|node| {
+                            node.get_attribute("data-loaded").map(str::to_owned)
+                        }),
+                    styles.first().map(|&nid| dom.text_content(nid)),
+                )
+            })
+            .expect("live DOM");
+
+        assert_eq!(
+            state.0.as_deref(),
+            Some("yes"),
+            "link load handler must run"
+        );
+        assert_eq!(
+            state.1.as_deref(),
+            Some(".target{color:red}"),
+            "the handler's `this.media = 'all'` must activate the sheet"
+        );
+    }
+
+    #[test]
+    fn true_print_stylesheet_loads_without_entering_screen_cascade() {
+        let dom = parse_html(
+            r#"<html><head>
+                <link id="print" rel="stylesheet" href="print.css" media="print"
+                      onload="this.setAttribute('data-loaded','yes')">
+            </head><body></body></html>"#,
+        );
+        let mut runtime = obscura_js::runtime::ObscuraJsRuntime::new();
+        runtime.set_dom(dom);
+        runtime.run_page_init();
+        runtime
+            .execute_script(
+                "<print-sheet>",
+                &materialize_linked_stylesheet_script(0, "body{display:none}"),
+            )
+            .expect("finish print linked sheet load");
+
+        let state = runtime
+            .with_dom(|dom| {
+                let link = dom
+                    .query_selector("#print")
+                    .expect("valid selector")
+                    .expect("print link");
+                (
+                    dom.get_node(link)
+                        .and_then(|node| {
+                            node.get_attribute("data-loaded").map(str::to_owned)
+                        }),
+                    dom.query_selector_all("style[data-obscura-external-stylesheets]")
+                        .expect("valid selector")
+                        .len(),
+                )
+            })
+            .expect("live DOM");
+
+        assert_eq!(
+            state.0.as_deref(),
+            Some("yes"),
+            "print link still fires load"
+        );
+        assert_eq!(
+            state.1, 0,
+            "print-only CSS must stay out of screen cascade"
+        );
+    }
+
     #[test]
     fn external_stylesheets_keep_their_positions_between_inline_sheets() {
         let dom = parse_html(

crates/obscura-render/src/dom.rs

@@ -4251,6 +4251,26 @@ fn is_full_span_column_subgrid(style: &crate::LayoutStyle) -> bool {
     )
 }
 
+/// Whether an item is wholly eligible for ordinary grid auto-placement.
+///
+/// The style model retains an explicit `grid-area:auto` as `Some(Line {
+/// Auto, Auto })`, while an omitted placement stays `None`. Both represent
+/// the same indefinite row and column spans to the grid placement algorithm.
+/// Raw named placements are never auto: an unresolved name must not enter the
+/// bounded subgrid reduction merely because it has no numeric `Line` yet.
+fn has_only_auto_grid_placement(style: &crate::LayoutStyle) -> bool {
+    if style.grid_column_raw.is_some() || style.grid_row_raw.is_some() {
+        return false;
+    }
+    let axis_is_auto = |line: Option<&taffy::Line<taffy::GridPlacement>>| {
+        line.is_none_or(|line| {
+            matches!(line.start, taffy::GridPlacement::Auto)
+                && matches!(line.end, taffy::GridPlacement::Auto)
+        })
+    };
+    axis_is_auto(style.grid_column.as_ref()) && axis_is_auto(style.grid_row.as_ref())
+}
+
 /// Collect the deliberately bounded Grid Level 2 subset used by broad
 /// "aligned rows" components: a full-span column subgrid, optionally nested
 /// through more full-span column subgrids, whose final children auto-place one
@@ -4331,7 +4351,9 @@ fn collect_column_subgrid_descendants(
         // This first subset intentionally excludes spanning and explicitly
         // placed items. It is the common data-row/card-row pattern and keeps
         // each descendant contribution attributable to one ancestor track.
-        if child_style.grid_column.is_some()
+        // Explicit `grid-area:auto` remains ordinary auto-placement in both
+        // axes and is therefore equivalent to omitting all placement values.
+        if !has_only_auto_grid_placement(child_style)
             || child_style.position == Some(taffy::Position::Absolute)
             || child_style.margin_auto[1]
             || child_style.margin_auto[3]

crates/obscura-render/src/paint.rs

@@ -3907,11 +3907,12 @@ fn background_image_rect(
             _ => None,
         }
     });
-    let (width, height) = if let Some(size) = expression_size {
-        size
-    } else if let Some(size) = explicit_size {
-        size
-    } else if let Some(fit) = fit {
+    // `cover` and `contain` are complete sizing algorithms, not contextual
+    // lengths. The style layer deliberately retains the authored token string
+    // for CSS math, so a keyword can also appear in `size_expression`; run the
+    // typed fit first or the unresolved token path falls back to the intrinsic
+    // size and silently bypasses fitting.
+    let (width, height) = if let Some(fit) = fit {
         let (iw, ih) = intrinsic?;
         let scale = match fit {
             crate::ObjectFit::Cover => (box_rect.width / iw).max(box_rect.height / ih),
@@ -3919,6 +3920,10 @@ fn background_image_rect(
             _ => 1.0,
         };
         (iw * scale, ih * scale)
+    } else if let Some(size) = expression_size {
+        size
+    } else if let Some(size) = explicit_size {
+        size
     } else {
         intrinsic.unwrap_or((box_rect.width, box_rect.height))
     };
@@ -6394,6 +6399,38 @@ mod tests {
         );
     }
 
+    #[test]
+    fn cover_and_contain_background_sizes_fit_the_positioning_area() {
+        let image = "data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20width='200'%20height='100'%3E%3Crect%20width='200'%20height='100'%20fill='blue'/%3E%3C/svg%3E";
+        let tree = parse_html(&format!(
+            r#"<html><body style="margin:0;background:white">
+               <div style="position:absolute;left:0;top:0;width:100px;height:200px;
+                 background:red url(&quot;{image}&quot;) center/cover no-repeat"></div>
+               <div style="position:absolute;left:100px;top:0;width:100px;height:200px;
+                 background-color:red;background-image:url(&quot;{image}&quot;);
+                 background-position:center;background-size:contain;background-repeat:no-repeat"></div>
+               </body></html>"#
+        ));
+        let pixmap = paint_dom(&tree, (200.0, 200.0), None).expect("pixmap");
+
+        let cover_edge = pixmap.pixel(50, 10).expect("cover edge");
+        assert!(
+            cover_edge.blue() > 200 && cover_edge.red() < 40,
+            "cover must scale the 2:1 image to the owner's 200px block axis: {cover_edge:?}"
+        );
+
+        let contain_outside = pixmap.pixel(150, 60).expect("contain letterbox");
+        assert!(
+            contain_outside.red() > 200 && contain_outside.blue() < 40,
+            "contain must leave the area outside its centered 100x50 image unpainted: {contain_outside:?}"
+        );
+        let contain_center = pixmap.pixel(150, 100).expect("contain center");
+        assert!(
+            contain_center.blue() > 200 && contain_center.red() < 40,
+            "contain must paint the fitted image through the center: {contain_center:?}"
+        );
+    }
+
     #[test]
     fn ordered_background_gradients_paint_every_translucent_layer() {
         let tree = parse_html(

crates/obscura-render/tests/layout_test.rs

@@ -2410,6 +2410,7 @@ fn nested_full_span_column_subgrid_shares_ancestor_tracks() {
             grid-column:1 / -1;
             grid-template-columns:subgrid;
           }
+          .inner > * { grid-area:auto }
           .inner { column-gap:20px }
           .leaf { height:20px }
           .a { width:40px }
@@ -2490,12 +2491,16 @@ fn unsafe_column_subgrid_cases_decline_the_fast_path() {
           }
           #narrow { width:200px }
           #partial { width:500px }
+          #placed { width:500px }
+          #named { width:500px }
           .subgrid, .inner {
             display:grid;
             grid-column:1 / -1;
             grid-template-columns:subgrid;
           }
           #partial-row { grid-column:1 / 3 }
+          #placed-b { grid-column:2 }
+          #named-b { grid-column:missing-line }
           .inner { column-gap:20px }
           .leaf { height:20px }
           .a { width:40px }
@@ -2516,6 +2521,20 @@ fn unsafe_column_subgrid_cases_decline_the_fast_path() {
             <div class="leaf c"></div>
           </div></div>
         </div>
+        <div id="placed" class="parent">
+          <div class="subgrid"><div class="inner">
+            <div class="leaf a"></div>
+            <div id="placed-b" class="leaf b"></div>
+            <div class="leaf c"></div>
+          </div></div>
+        </div>
+        <div id="named" class="parent">
+          <div class="subgrid"><div class="inner">
+            <div class="leaf a"></div>
+            <div id="named-b" class="leaf b"></div>
+            <div class="leaf c"></div>
+          </div></div>
+        </div>
         "#,
     );
     let layout = layout_dom(&tree, (800.0, 600.0));
@@ -2524,6 +2543,10 @@ fn unsafe_column_subgrid_cases_decline_the_fast_path() {
     let narrow_b = rect("narrow-b");
     let partial = rect("partial");
     let partial_b = rect("partial-b");
+    let placed = rect("placed");
+    let placed_b = rect("placed-b");
+    let named = rect("named");
+    let named_b = rect("named-b");
 
     assert!(
         (narrow.height - 60.0).abs() < 0.01 && (narrow_b.x - narrow.x).abs() < 0.01,
@@ -2533,6 +2556,16 @@ fn unsafe_column_subgrid_cases_decline_the_fast_path() {
         (partial.height - 60.0).abs() < 0.01 && (partial_b.x - partial.x).abs() < 0.01,
         "partial-span subgrid must retain the stacked fallback: {partial:?} {partial_b:?}"
     );
+    assert!(
+        (placed.height - 40.0).abs() < 0.01 && placed_b.x > placed.x,
+        "an explicitly placed leaf must retain the existing placement fallback: \
+         {placed:?} {placed_b:?}"
+    );
+    assert!(
+        (named.height - 60.0).abs() < 0.01 && (named_b.x - named.x).abs() < 0.01,
+        "an unresolved named placement must not enter the numeric subgrid reduction: \
+         {named:?} {named_b:?}"
+    );
 }
 
 #[test]