fix: guard against zero-length clip at EOF

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/utils/clipRange.ts

@@ -8,21 +8,25 @@ export function computeQuickClipRange(
 ): { start: number; end: number } | null {
   if (duration === 0) return null;
 
+  let start: number;
+  let end: number;
+
   switch (position) {
     case 'at':
-      return {
+      start = currentTime;
-        start: currentTime,
+      end = Math.min(currentTime + clipDuration, duration);
-        end: Math.min(currentTime + clipDuration, duration),
+      break;
-      };
     case 'before':
-      return {
+      start = Math.max(currentTime - clipDuration, 0);
-        start: Math.max(currentTime - clipDuration, 0),
+      end = currentTime;
-        end: currentTime,
+      break;
-      };
     default: {
       const _exhaustive: never = position;
       void _exhaustive;
       return null;
     }
   }
+
+  if (start >= end) return null;
+  return { start, end };
 }

tests/lib/utils/clipRange.test.ts

@@ -40,4 +40,8 @@ describe('computeQuickClipRange', () => {
     const result = computeQuickClipRange(120, 120, 'before');
     expect(result).toEqual({ start: 110, end: 120 });
   });
+
+  it('"at" returns null when currentTime equals duration', () => {
+    expect(computeQuickClipRange(120, 120, 'at')).toBeNull();
+  });
 });