test: add regression test for WEBP RIFF padding (#8527) (#11267)

## Summary

Add a regression test for #8527 (handle RIFF padding for odd-sized WEBP
chunks). The fix added + (chunk_length % 2) to the chunk-stride
calculation in getWebpMetadata so EXIF chunks following an odd-sized
chunk are still located correctly. There was no existing unit test
covering getWebpMetadata, so without a regression test the fix could
silently break in a future
  refactor. 

## Changes

- **What**: 
- New unit test file src/scripts/pnginfo.test.ts covering
getWebpMetadata's RIFF chunk traversal.
- Helpers build a minimal in-memory WEBP with one VP8 chunk of
configurable length followed by an EXIF chunk encoding workflow:<json>.
- Odd-length case (regression for #8527): without the % 2 padding
adjustment, the parser walks one byte short and returns {}.
- Even-length case: guards against an over-correction that always adds
1.
- Verified RED→GREEN locally.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-11267-test-add-regression-test-for-WEBP-RIFF-padding-8527-3436d73d36508117a66edf3cb108ded0)
by [Unito](https://www.unito.io)

src/scripts/pnginfo.test.ts

@@ -0,0 +1,67 @@
+import { describe, expect, it } from 'vitest'
+
+import { getWebpMetadata } from './pnginfo'
+
+function buildExifPayload(workflowJson: string): Uint8Array {
+  const fullStr = `workflow:${workflowJson}\0`
+  const strBytes = new TextEncoder().encode(fullStr)
+
+  const headerSize = 22
+  const buf = new Uint8Array(headerSize + strBytes.length)
+  const dv = new DataView(buf.buffer)
+
+  buf.set([0x49, 0x49], 0)
+  dv.setUint16(2, 0x002a, true)
+  dv.setUint32(4, 8, true)
+  dv.setUint16(8, 1, true)
+  dv.setUint16(10, 0, true)
+  dv.setUint16(12, 2, true)
+  dv.setUint32(14, strBytes.length, true)
+  dv.setUint32(18, 22, true)
+  buf.set(strBytes, 22)
+
+  return buf
+}
+
+function buildWebp(precedingChunkLength: number, workflowJson: string): File {
+  const exifPayload = buildExifPayload(workflowJson)
+  const precedingPadded = precedingChunkLength + (precedingChunkLength % 2)
+  const totalSize = 12 + (8 + precedingPadded) + (8 + exifPayload.length)
+
+  const buffer = new Uint8Array(totalSize)
+  const dv = new DataView(buffer.buffer)
+
+  buffer.set([0x52, 0x49, 0x46, 0x46], 0)
+  dv.setUint32(4, totalSize - 8, true)
+  buffer.set([0x57, 0x45, 0x42, 0x50], 8)
+
+  buffer.set([0x56, 0x50, 0x38, 0x20], 12)
+  dv.setUint32(16, precedingChunkLength, true)
+
+  const exifStart = 20 + precedingPadded
+  buffer.set([0x45, 0x58, 0x49, 0x46], exifStart)
+  dv.setUint32(exifStart + 4, exifPayload.length, true)
+  buffer.set(exifPayload, exifStart + 8)
+
+  return new File([buffer], 'test.webp', { type: 'image/webp' })
+}
+
+describe('getWebpMetadata', () => {
+  it('finds workflow when a preceding chunk has odd length (RIFF padding)', async () => {
+    const workflow = '{"nodes":[]}'
+    const file = buildWebp(3, workflow)
+
+    const metadata = await getWebpMetadata(file)
+
+    expect(metadata.workflow).toBe(workflow)
+  })
+
+  it('finds workflow when preceding chunk has even length (no padding)', async () => {
+    const workflow = '{"nodes":[1]}'
+    const file = buildWebp(4, workflow)
+
+    const metadata = await getWebpMetadata(file)
+
+    expect(metadata.workflow).toBe(workflow)
+  })
+})