diff --git a/frontend/src/lib/thumbnails.test.ts b/frontend/src/lib/thumbnails.test.ts
deleted file mode 100644
index aad48268..00000000
--- a/frontend/src/lib/thumbnails.test.ts
+++ /dev/null
@@ -1,37 +0,0 @@
-import { describe, expect, it } from 'vitest';
-import { thumbnailUrl } from './thumbnails';
-
-describe('thumbnailUrl', () => {
-	it('returns null when thumbnailKey is undefined', () => {
-		expect(thumbnailUrl({ id: 'abc' })).toBeNull();
-	});
-
-	it('returns url without version param when thumbnailKey present but generatedAt missing', () => {
-		expect(thumbnailUrl({ id: 'abc', thumbnailKey: 'thumbnails/abc.jpg' })).toBe(
-			'/api/documents/abc/thumbnail'
-		);
-	});
-
-	it('appends encoded cache-bust param when generatedAt present', () => {
-		const url = thumbnailUrl({
-			id: 'abc',
-			thumbnailKey: 'thumbnails/abc.jpg',
-			thumbnailGeneratedAt: '2026-04-22T20:41:15.123456'
-		});
-		expect(url).toBe('/api/documents/abc/thumbnail?v=2026-04-22T20%3A41%3A15.123456');
-	});
-
-	it('different generatedAt produces different URL — enables cache-bust on file replace', () => {
-		const a = thumbnailUrl({
-			id: 'x',
-			thumbnailKey: 'thumbnails/x.jpg',
-			thumbnailGeneratedAt: '2026-01-01T10:00:00'
-		});
-		const b = thumbnailUrl({
-			id: 'x',
-			thumbnailKey: 'thumbnails/x.jpg',
-			thumbnailGeneratedAt: '2026-01-01T11:00:00'
-		});
-		expect(a).not.toBe(b);
-	});
-});
diff --git a/frontend/src/lib/thumbnails.ts b/frontend/src/lib/thumbnails.ts
deleted file mode 100644
index 47a0a606..00000000
--- a/frontend/src/lib/thumbnails.ts
+++ /dev/null
@@ -1,18 +0,0 @@
-type ThumbnailDoc = {
-	id: string;
-	thumbnailKey?: string;
-	thumbnailGeneratedAt?: string;
-};
-
-/**
- * Builds the URL for a document thumbnail image, or returns null when the document
- * has no thumbnail yet. When `thumbnailGeneratedAt` is present it is appended as a
- * `?v=…` query param so the browser / proxy cache is invalidated whenever the file
- * is replaced (the backend regenerates thumbnails at the same S3 key on replace).
- */
-export function thumbnailUrl(doc: ThumbnailDoc): string | null {
-	if (!doc.thumbnailKey) return null;
-	const base = `/api/documents/${doc.id}/thumbnail`;
-	if (!doc.thumbnailGeneratedAt) return base;
-	return `${base}?v=${encodeURIComponent(doc.thumbnailGeneratedAt)}`;
-}