d2svg: respect reduced motion for animated connections

ci/release/changelogs/next.md

@@ -19,6 +19,7 @@
 - exports: pptx follows standards more closely, addressing warnings from some Powerpoint software [#2645](https://github.com/terrastruct/d2/pull/2645)
 - d2sequence: fix edge case of invalid sequence diagrams [#2660](https://github.com/terrastruct/d2/pull/2660)
 - d2svg: Text may overflow legend bounds when monospace font is used [#2674](https://github.com/terrastruct/d2/pull/2674)
+- d2svg: animated connections honor reduced motion preferences [#2778](https://github.com/terrastruct/d2/pull/2778)
 
 ---
 

d2renderers/d2svg/d2svg.go

@@ -2519,6 +2519,12 @@ func EmbedFonts(buf *bytes.Buffer, diagramHash, source string, fontFamily *d2fon
 		stroke-dashoffset: 0;
 	}
 }
+
+@media (prefers-reduced-motion: reduce) {
+	.animated-connection {
+		animation: none !important;
+	}
+}
 `,
 	)
 

d2renderers/d2svg/d2svg_test.go

@@ -1,11 +1,35 @@
 package d2svg
 
 import (
+	"bytes"
+	"strings"
 	"testing"
 
+	"oss.terrastruct.com/d2/d2renderers/d2fonts"
 	"oss.terrastruct.com/d2/d2target"
 )
 
+func TestEmbedFontsReducedMotion(t *testing.T) {
+	var buf bytes.Buffer
+	fontFamily := d2fonts.SourceSansPro
+	monoFontFamily := d2fonts.SourceCodePro
+	EmbedFonts(&buf, "diagram", `<path class="animated-connection" />`, &fontFamily, &monoFontFamily, "")
+
+	css := buf.String()
+	if !strings.Contains(css, "@media (prefers-reduced-motion: reduce)") {
+		t.Fatal("animated connections should honor the reduced-motion preference")
+	}
+	if !strings.Contains(css, "animation: none !important;") {
+		t.Fatal("reduced-motion rule should override the inline connection animation")
+	}
+
+	buf.Reset()
+	EmbedFonts(&buf, "diagram", `<path class="connection" />`, &fontFamily, &monoFontFamily, "")
+	if strings.Contains(buf.String(), "prefers-reduced-motion") {
+		t.Fatal("static diagrams should not include the reduced-motion rule")
+	}
+}
+
 func TestSortObjects(t *testing.T) {
 	allObjects := []DiagramObject{
 		// same zIndex and level, should keep in this order