diff --git a/packages/@uppy/aws-s3/tests/index.test.ts b/packages/@uppy/aws-s3/tests/index.test.ts
index d3c9490af..35201311e 100644
--- a/packages/@uppy/aws-s3/tests/index.test.ts
+++ b/packages/@uppy/aws-s3/tests/index.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, it, vi } from 'vitest'
+import { afterEach, describe, expect, it, vi } from 'vitest'
 
 import 'whatwg-fetch'
 import Core, { type Meta, type UppyFile } from '@uppy/core'
@@ -7,6 +7,103 @@ import AwsS3, { type AwsBody, type AwsS3Options } from '../src/index.js'
 const KB = 1024
 const MB = KB * KB
 
+// ---------------------------------------------------------------------------
+// Helpers for multipart upload tests
+// ---------------------------------------------------------------------------
+
+/** Minimal XML responses that S3 returns for multipart operations */
+const s3Responses = {
+  createMultipart: (uploadId: string, key: string) =>
+    `<?xml version="1.0" encoding="UTF-8"?>
+     <InitiateMultipartUploadResult>
+       <UploadId>${uploadId}</UploadId>
+       <Key>${key}</Key>
+     </InitiateMultipartUploadResult>`,
+
+  uploadPart: (etag: string) => '',
+
+  listParts: (parts: { partNumber: number; etag: string }[]) =>
+    `<?xml version="1.0" encoding="UTF-8"?>
+     <ListPartsResult>
+       ${parts.map((p) => `<Part><PartNumber>${p.partNumber}</PartNumber><ETag>${p.etag}</ETag></Part>`).join('')}
+     </ListPartsResult>`,
+
+  completeMultipart: (location: string, key: string) =>
+    `<?xml version="1.0" encoding="UTF-8"?>
+     <CompleteMultipartUploadResult>
+       <Location>${location}</Location>
+       <Key>${key}</Key>
+       <Bucket>test-bucket</Bucket>
+     </CompleteMultipartUploadResult>`,
+
+  abortMultipart: () => '',
+}
+
+/**
+ * Creates mock signRequest + fetch for multipart upload tests.
+ * signRequest encodes the operation in the URL so fetchMock can route correctly.
+ */
+function createMultipartMocks(opts: { uploadId?: string; key?: string } = {}) {
+  const uploadId = opts.uploadId ?? 'test-upload-id'
+  const key = opts.key ?? 'test-key'
+
+  // signRequest encodes operation details in the URL for fetchMock routing
+  const signRequest = vi.fn().mockImplementation(async (req: any) => {
+    const params = new URLSearchParams()
+    if (req.uploadId) params.set('uploadId', req.uploadId)
+    if (req.partNumber) params.set('partNumber', String(req.partNumber))
+    params.set('method', req.method)
+    return {
+      url: `https://test-bucket.s3.us-east-1.amazonaws.com/${req.key || key}?${params}`,
+    }
+  })
+
+  const operations: string[] = []
+
+  const fetchMock = vi.fn().mockImplementation(async (url: string | Request, init?: any) => {
+    const urlStr = typeof url === 'string' ? url : url.url
+    const method = init?.method || 'GET'
+    const params = new URL(urlStr).searchParams
+    const hasUploadId = params.has('uploadId')
+
+    if (method === 'POST' && !hasUploadId) {
+      operations.push('createMultipart')
+      return new Response(s3Responses.createMultipart(uploadId, key), {
+        status: 200,
+        headers: { 'Content-Type': 'application/xml' },
+      })
+    }
+    if (method === 'PUT') {
+      operations.push('uploadPart')
+      return new Response('', {
+        status: 200,
+        headers: { ETag: '"etag-1"' },
+      })
+    }
+    if (method === 'POST' && hasUploadId) {
+      operations.push('completeMultipart')
+      return new Response(
+        s3Responses.completeMultipart(`https://test-bucket.s3.amazonaws.com/${key}`, key),
+        { status: 200, headers: { 'Content-Type': 'application/xml' } },
+      )
+    }
+    if (method === 'GET' && hasUploadId) {
+      operations.push('listParts')
+      return new Response(s3Responses.listParts([]), {
+        status: 200,
+        headers: { 'Content-Type': 'application/xml' },
+      })
+    }
+    if (method === 'DELETE') {
+      operations.push('abortMultipart')
+      return new Response('', { status: 204 })
+    }
+    return new Response('Not Found', { status: 404 })
+  })
+
+  return { signRequest, fetchMock, operations, uploadId, key }
+}
+
 describe('AwsS3', () => {
   it('Registers AwsS3 upload plugin', () => {
     const core = new Core().use(AwsS3, {
@@ -244,4 +341,153 @@ describe('AwsS3', () => {
       expect(result?.successful).toHaveLength(0)
     })
   })
+
+  describe('Golden Retriever resume state (s3Multipart)', () => {
+    const originalFetch = globalThis.fetch
+
+    afterEach(() => {
+      globalThis.fetch = originalFetch
+    })
+
+    it('persists s3Multipart on file state after creating multipart upload', async () => {
+      const { signRequest, fetchMock, uploadId } = createMultipartMocks()
+      // After createMultipart succeeds, hang on uploadPart so we can inspect state
+      fetchMock.mockImplementation(async (url: string | Request, init?: any) => {
+        const urlStr = typeof url === 'string' ? url : url.url
+        const method = init?.method || 'GET'
+        const hasUploadId = new URL(urlStr).searchParams.has('uploadId')
+
+        if (method === 'POST' && !hasUploadId) {
+          return new Response(
+            s3Responses.createMultipart(uploadId, 'test-key'),
+            { status: 200, headers: { 'Content-Type': 'application/xml' } },
+          )
+        }
+        // Hang on everything else — we only need createMultipart to complete
+        return new Promise(() => {})
+      })
+      globalThis.fetch = fetchMock
+
+      const core = new Core().use(AwsS3, {
+        bucket: 'test-bucket',
+        region: 'us-east-1',
+        signRequest,
+        shouldUseMultipart: true,
+      })
+
+      const fileId = core.addFile({
+        source: 'test',
+        name: 'big.dat',
+        type: 'application/octet-stream',
+        data: new File([new Uint8Array(6 * MB)], 'big.dat'),
+      })
+
+      const uploadPromise = core.upload()
+
+      // Wait for createMultipart to complete and state to be persisted
+      await new Promise((resolve) => setTimeout(resolve, 100))
+
+      const file = core.getFile(fileId)
+      expect(file.s3Multipart).toBeDefined()
+      expect(file.s3Multipart?.uploadId).toBe(uploadId)
+
+      // Clean up
+      core.cancelAll()
+      await uploadPromise
+    })
+
+    it('clears s3Multipart when upload is aborted via cancelAll', async () => {
+      const { signRequest, fetchMock } = createMultipartMocks()
+      fetchMock.mockImplementation(async (url: string | Request, init?: any) => {
+        const urlStr = typeof url === 'string' ? url : url.url
+        const method = init?.method || 'GET'
+        const hasUploadId = new URL(urlStr).searchParams.has('uploadId')
+
+        if (method === 'POST' && !hasUploadId) {
+          return new Response(
+            s3Responses.createMultipart('cancel-test-id', 'cancel-key'),
+            { status: 200, headers: { 'Content-Type': 'application/xml' } },
+          )
+        }
+        if (method === 'DELETE') {
+          return new Response('', { status: 204 })
+        }
+        // Hang on everything else
+        return new Promise(() => {})
+      })
+      globalThis.fetch = fetchMock
+
+      const core = new Core().use(AwsS3, {
+        bucket: 'test-bucket',
+        region: 'us-east-1',
+        signRequest,
+        shouldUseMultipart: true,
+      })
+
+      const fileId = core.addFile({
+        source: 'test',
+        name: 'big.dat',
+        type: 'application/octet-stream',
+        data: new File([new Uint8Array(6 * MB)], 'big.dat'),
+      })
+
+      const uploadPromise = core.upload()
+
+      // Wait for createMultipart, then cancel
+      await new Promise((resolve) => setTimeout(resolve, 50))
+      core.cancelAll()
+
+      await uploadPromise
+
+      const file = core.getFile(fileId)
+      // s3Multipart should be cleared so retries don't use a dead uploadId
+      expect(file?.s3Multipart).toBeUndefined()
+    })
+
+    it('uses persisted s3Multipart key for resume (listParts, not createMultipart)', async () => {
+      const persistedKey = 'persisted-object-key'
+      const persistedUploadId = 'persisted-upload-id'
+      const { signRequest, fetchMock, operations } = createMultipartMocks({
+        uploadId: persistedUploadId,
+        key: persistedKey,
+      })
+      globalThis.fetch = fetchMock
+
+      const core = new Core().use(AwsS3, {
+        bucket: 'test-bucket',
+        region: 'us-east-1',
+        signRequest,
+        shouldUseMultipart: false, // Would normally be simple upload
+      })
+
+      const fileId = core.addFile({
+        source: 'test',
+        name: 'big.dat',
+        type: 'application/octet-stream',
+        data: new File([new Uint8Array(6 * MB)], 'big.dat'),
+      })
+
+      // Simulate Golden Retriever restoring s3Multipart state
+      core.setFileState(fileId, {
+        s3Multipart: { uploadId: persistedUploadId, key: persistedKey },
+      })
+
+      const uploadPromise = core.upload()
+
+      // Wait for the resume flow to call listParts (via fetch), then cancel
+      await new Promise((resolve) => setTimeout(resolve, 100))
+
+      // Should have resumed (listParts) instead of creating a new multipart upload
+      expect(operations).toContain('listParts')
+      expect(operations).not.toContain('createMultipart')
+
+      // The signRequest calls should use the persisted key, not a generated one
+      const signedKeys = signRequest.mock.calls.map((call: any) => call[0].key)
+      expect(signedKeys.every((k: string) => k === persistedKey)).toBe(true)
+
+      // Clean up
+      core.cancelAll()
+      await uploadPromise
+    })
+  })
 })