Fix keyframe easing detection

Serialize effective per-keyframe easing back into the linked stylesheet corpus so overshoot motion is detected. Add a browser regression with a neutral animation name.\n\nAI assistance disclosure: Codex helped implement and test this fix under maintainer direction.

cli/engine/browser/injected/index.mjs

@@ -1547,6 +1547,10 @@ if (IS_BROWSER) {
         const declarations = Object.entries(frame)
           .filter(([property, value]) => !metadata.has(property) && value != null && value !== '')
           .map(([property, value]) => `${cssPropertyName(property)}: ${value};`);
+        const easing = String(frame.easing || '').trim();
+        if (easing && easing.toLowerCase() !== 'linear') {
+          declarations.push(`animation-timing-function: ${easing};`);
+        }
         if (declarations.length === 0) continue;
         blocks.push(`${offset}% { ${declarations.join(' ')} }`);
       }

cli/engine/detect-antipatterns-browser.js

@@ -8451,6 +8451,10 @@ if (IS_BROWSER) {
         const declarations = Object.entries(frame)
           .filter(([property, value]) => !metadata.has(property) && value != null && value !== '')
           .map(([property, value]) => `${cssPropertyName(property)}: ${value};`);
+        const easing = String(frame.easing || '').trim();
+        if (easing && easing.toLowerCase() !== 'linear') {
+          declarations.push(`animation-timing-function: ${easing};`);
+        }
         if (declarations.length === 0) continue;
         blocks.push(`${offset}% { ${declarations.join(' ')} }`);
       }

tests/detect-antipatterns-browser.test.mjs

@@ -1469,7 +1469,8 @@ describe('detectUrl — browser-only fixtures', () => {
       assert.equal(grids[0].severity, 'advisory');
       assert.equal(grids[0].advisory, true);
       assert.equal(
-        linkedFindings.some(finding => finding.type === 'bounce-easing'),
+        linkedFindings.some(finding => finding.type === 'bounce-easing'
+          && finding.detail === 'cubic-bezier(0.34, 1.56, 0.64, 1)'),
         true,
         JSON.stringify({ linkedFindings, linkedCssom }),
       );

tests/fixtures/antipatterns/linked-url-patterns.css

@@ -47,6 +47,18 @@ main > ::before {
   to { transform: translateX(-50%); }
 }
 
+.linked-keyframe-overshoot {
+  animation: linked-keyframe-curve 2s linear infinite;
+}
+
+@keyframes linked-keyframe-curve {
+  from {
+    transform: translateY(0);
+    animation-timing-function: cubic-bezier(0.34, 1.56, 0.64, 1);
+  }
+  to { transform: translateY(2px); }
+}
+
 .overridden-keyframes-animation {
   animation: overridden-horizontal-loop 2s linear infinite;
 }

tests/fixtures/antipatterns/linked-url-patterns.html

@@ -12,6 +12,7 @@
     <div data-decoy="">Empty attribute-value decoy</div>
     <div class="::before">Escaped identifier selector</div>
     <div class="linked-marquee">Rendered linked marquee animation</div>
+    <div class="linked-keyframe-overshoot">Rendered linked keyframe easing</div>
     <div class="overridden-keyframes-animation">Overridden linked keyframes</div>
     <div class="layered-keyframes-animation">Layer-priority linked keyframes</div>
     <div class="linked-pulse-dot"></div>