fix(print): flex-fallback grids with a grid-heading for WeasyPrint

src/slidr/render/templates/base.css

@@ -429,6 +429,20 @@ section[data-transition]:not([data-transition="none"]).outgoing {
     max-height: none;
     overflow: visible;
   }
+
+  /* WeasyPrint mis-sizes 1fr grid tracks when a full-width spanning
+     grid-heading (grid-column: 1 / -1) is present, collapsing the
+     sibling cards to near-zero width. Fall back to flexbox for these
+     grids in print only; grids without a grid-heading are untouched. */
+  .grid:has(> .grid-heading) {
+    display: flex !important;
+    flex-wrap: wrap;
+    align-items: flex-start;
+    gap: var(--gap);
+  }
+  .grid:has(> .grid-heading) > .grid-heading { flex: 0 0 100%; }
+  .grid:has(> .grid-heading) > .card:not(.grid-heading) { flex: 1 1 0; min-width: 0; }
+  .grid:has(> .grid-heading) > .card.side-image { flex: 0 0 auto; }
 }
 
 @page {

tests/test_html.py

@@ -1,9 +1,24 @@
 """Tests for the HTML renderer's element rendering."""
 
-from slidr.render.html import _render_elem
+from slidr.render.html import _render_elem, base_css
 from slidr.render.ir import Elem
 
 
+def test_print_css_flexes_grids_with_a_grid_heading():
+    """Print stylesheet falls back to flexbox for grids with a grid-heading.
+
+    WeasyPrint mis-sizes `1fr` grid tracks when a full-width spanning
+    grid-heading (`grid-column: 1 / -1`) is present, collapsing the sibling
+    cards to near-zero width. The print CSS must convert those grids to
+    flexbox; grids without a grid-heading must stay on the grid path.
+    """
+    css = base_css()
+    assert ".grid:has(> .grid-heading)" in css
+    assert ".grid:has(> .grid-heading) > .grid-heading" in css
+    # The grid-heading spans a full row in the flex fallback.
+    assert "flex: 0 0 100%" in css
+
+
 def test_speaker_linkedin_uses_brand_svg_not_placeholder():
     """linkedin= renders the inlined brand mark, never a Lucide placeholder.