feat: open multi-part packages in browser

src/App.test.tsx

@@ -52,10 +52,14 @@ class SuccessfulParserWorker implements WorkerPort {
   onmessage: ((event: MessageEvent<WorkerResponse>) => void) | null = null;
   onerror: ((event: ErrorEvent) => void) | null = null;
   terminated = false;
+  lastMessage: WorkerRequest | undefined;
+  lastTransfer: Transferable[] = [];
 
   constructor(private readonly packageResult?: OneNotePackageDto) {}
 
-  postMessage(message: WorkerRequest): void {
+  postMessage(message: WorkerRequest, transfer: Transferable[] = []): void {
+    this.lastMessage = message;
+    this.lastTransfer = transfer;
     queueMicrotask(() => {
       if (message.type === 'parse-one') {
         this.respond({
@@ -158,7 +162,7 @@ describe('OneNoteApplication', () => {
     );
 
     await user.upload(
-      screen.getByLabelText('Choose a OneNote file'),
+      screen.getByLabelText('Choose OneNote files'),
       new File([new Uint8Array([1, 2, 3])], 'Section.one')
     );
 
@@ -189,23 +193,74 @@ describe('OneNoteApplication', () => {
       tree: { interpreted: false, nodes: [] },
       diagnostics: [],
     };
+    const worker = new SuccessfulParserWorker(notebook);
     render(
       <OneNoteApplication
-        createWorkerClient={() =>
+        createWorkerClient={() => new OneNoteWorkerClient(() => worker)}
-          new OneNoteWorkerClient(() => new SuccessfulParserWorker(notebook))
-        }
       />
     );
 
+    const part3 = new File([new Uint8Array([3])], 'Notebook-3.cab');
+    const primary = new File([new Uint8Array([1])], 'Notebook.onepkg');
+    const part2 = new File([new Uint8Array([2])], 'Notebook-2.cab');
     fireEvent.drop(screen.getByTestId('file-drop-zone'), {
       dataTransfer: {
-        files: [new File([new Uint8Array([1])], 'Notebook.onepkg')],
+        files: [part3, primary, part2],
       },
     });
 
     expect(
       await screen.findByRole('heading', { name: 'Package summary' })
     ).toBeInTheDocument();
+    expect(worker.lastMessage).toEqual(
+      expect.objectContaining({
+        type: 'parse-onepkg',
+        fileName: 'Notebook.onepkg',
+        cabinetParts: [
+          expect.objectContaining({ fileName: 'Notebook-3.cab' }),
+          expect.objectContaining({ fileName: 'Notebook-2.cab' }),
+        ],
+      })
+    );
+    expect(worker.lastTransfer).toHaveLength(3);
+  });
+
+  it('hands a multi-file picker selection to the package worker', async () => {
+    const notebook: OneNotePackageDto = {
+      format: 'onepkg',
+      sourceName: 'Notebook.onepkg',
+      sourceSize: 2,
+      entries: [],
+      sections: [],
+      tree: { interpreted: false, nodes: [] },
+      diagnostics: [],
+    };
+    const worker = new SuccessfulParserWorker(notebook);
+    const user = userEvent.setup();
+    render(
+      <OneNoteApplication
+        createWorkerClient={() => new OneNoteWorkerClient(() => worker)}
+      />
+    );
+
+    const input = screen.getByLabelText('Choose OneNote files');
+    expect(input).toHaveAttribute('multiple');
+    expect(input).toHaveAttribute('accept', '.one,.onepkg,.cab');
+    await user.upload(input, [
+      new File([new Uint8Array([2])], 'Notebook-2.cab'),
+      new File([new Uint8Array([1])], 'Notebook.onepkg'),
+    ]);
+
+    expect(
+      await screen.findByRole('heading', { name: 'Package summary' })
+    ).toBeInTheDocument();
+    expect(worker.lastMessage).toEqual(
+      expect.objectContaining({
+        type: 'parse-onepkg',
+        fileName: 'Notebook.onepkg',
+        cabinetParts: [expect.objectContaining({ fileName: 'Notebook-2.cab' })],
+      })
+    );
   });
 
   it('keeps a failed packaged section visible beside a readable one', async () => {
@@ -299,7 +354,7 @@ describe('OneNoteApplication', () => {
     );
 
     await user.upload(
-      screen.getByLabelText('Choose a OneNote file'),
+      screen.getByLabelText('Choose OneNote files'),
       new File([new Uint8Array([1])], 'Notebook.onepkg')
     );
 
@@ -336,7 +391,7 @@ describe('OneNoteApplication', () => {
     );
 
     await user.upload(
-      screen.getByLabelText('Choose a OneNote file'),
+      screen.getByLabelText('Choose OneNote files'),
       new File(['not OneNote'], 'Broken.one')
     );
 
@@ -353,12 +408,12 @@ describe('OneNoteApplication', () => {
     render(<OneNoteApplication />);
 
     await user.upload(
-      screen.getByLabelText('Choose a OneNote file'),
+      screen.getByLabelText('Choose OneNote files'),
       new File(['not a notebook'], 'notes.zip')
     );
 
     expect(await screen.findByRole('alert')).toHaveTextContent(
-      'Choose a file whose name ends in .one or .onepkg.'
+      'Choose one .one file, or one .onepkg file together with its .cab parts.'
     );
   });
 
@@ -371,7 +426,7 @@ describe('OneNoteApplication', () => {
       value: MAX_SOURCE_FILE_BYTES + 1,
     });
 
-    await user.upload(screen.getByLabelText('Choose a OneNote file'), file);
+    await user.upload(screen.getByLabelText('Choose OneNote files'), file);
 
     expect(await screen.findByRole('alert')).toHaveTextContent('512 MiB');
   });

src/App.tsx

@@ -20,10 +20,7 @@ import type {
   OneNoteSectionDto,
 } from './onenote/model/dto.js';
 import type { ParserDiagnostic } from './onenote/model/diagnostics.js';
-import {
+import { selectSourceFiles } from './source-file.js';
-  MAX_SOURCE_FILE_BYTES,
-  sourceKindFromFileName,
-} from './source-file.js';
 import { toolboxApp } from './toolbox/manifest.js';
 import {
   OneNoteWorkerClient,
@@ -174,21 +171,13 @@ export function OneNoteApplication({
     }
   };
 
-  const openFile = async (file: File) => {
+  const openFiles = async (files: File[]) => {
-    const sourceKind = sourceKindFromFileName(file.name);
+    const selection = selectSourceFiles(files);
-    if (!sourceKind) {
+    if (!selection.ok) {
       setState({
         phase: 'error',
-        title: 'Unsupported file name',
+        title: selection.title,
-        message: 'Choose a file whose name ends in .one or .onepkg.',
+        message: selection.message,
-      });
-      return;
-    }
-    if (file.size > MAX_SOURCE_FILE_BYTES) {
-      setState({
-        phase: 'error',
-        title: 'File is too large',
-        message: 'The selected file exceeds the current 512 MiB safety limit.',
       });
       return;
     }
@@ -201,12 +190,24 @@ export function OneNoteApplication({
     activeClient.current = client;
     setSelectedSectionId(undefined);
     setPageState({ phase: 'empty' });
-    setState({ phase: 'reading', fileName: file.name });
+    setState({ phase: 'reading', fileName: selection.source.name });
 
     try {
-      const bytes = await file.arrayBuffer();
+      const buffers = await Promise.all(
+        [selection.source, ...selection.cabinetParts].map((file) =>
+          file.arrayBuffer()
+        )
+      );
       if (generation.current !== requestGeneration) return;
-      const response = await client.parseSource(sourceKind, file.name, bytes);
+      const response = await client.parseSource(
+        selection.kind,
+        selection.source.name,
+        buffers[0]!,
+        selection.cabinetParts.map((part, index) => ({
+          fileName: part.name,
+          bytes: buffers[index + 1]!,
+        }))
+      );
       if (generation.current !== requestGeneration) return;
 
       if (response.type === 'failure') {
@@ -226,7 +227,7 @@ export function OneNoteApplication({
       if (response.type === 'section') {
         setState({
           phase: 'loaded',
-          fileName: file.name,
+          fileName: selection.source.name,
           source: {
             kind: 'one',
             sessionId: response.sessionId,
@@ -253,7 +254,7 @@ export function OneNoteApplication({
       setSelectedSectionId(preferredSection?.id);
       setState({
         phase: 'loaded',
-        fileName: file.name,
+        fileName: selection.source.name,
         source: {
           kind: 'onepkg',
           sessionId: response.sessionId,
@@ -373,7 +374,7 @@ export function OneNoteApplication({
   return (
     <main className="application">
       {state.phase === 'idle' ? (
-        <FileDropZone onFile={(file) => void openFile(file)} />
+        <FileDropZone onFiles={(files) => void openFiles(files)} />
       ) : null}
 
       {state.phase === 'reading' ? (

src/components/FileDropZone.tsx

@@ -2,25 +2,25 @@ import { useRef, useState, type ChangeEvent, type DragEvent } from 'react';
 
 interface FileDropZoneProps {
   disabled?: boolean;
-  onFile(file: File): void;
+  onFiles(files: File[]): void;
 }
 
-export function FileDropZone({ disabled = false, onFile }: FileDropZoneProps) {
+export function FileDropZone({ disabled = false, onFiles }: FileDropZoneProps) {
   const input = useRef<HTMLInputElement>(null);
   const [dragging, setDragging] = useState(false);
 
-  const selectFile = (event: ChangeEvent<HTMLInputElement>) => {
+  const selectFiles = (event: ChangeEvent<HTMLInputElement>) => {
-    const file = event.target.files?.[0];
+    const files = [...(event.target.files ?? [])];
     event.target.value = '';
-    if (file) onFile(file);
+    if (files.length > 0) onFiles(files);
   };
 
-  const dropFile = (event: DragEvent<HTMLDivElement>) => {
+  const dropFiles = (event: DragEvent<HTMLDivElement>) => {
     event.preventDefault();
     setDragging(false);
     if (disabled) return;
-    const file = event.dataTransfer.files[0];
+    const files = [...event.dataTransfer.files];
-    if (file) onFile(file);
+    if (files.length > 0) onFiles(files);
   };
 
   return (
@@ -36,23 +36,24 @@ export function FileDropZone({ disabled = false, onFile }: FileDropZoneProps) {
           setDragging(false);
         }
       }}
-      onDrop={dropFile}
+      onDrop={dropFiles}
       data-testid="file-drop-zone"
     >
       <p className="drop-zone__eyebrow">Private, local-first reader</p>
       <h2>Open a OneNote file</h2>
       <p>
-        Inspect a <code>.one</code> section or <code>.onepkg</code> notebook
+        Inspect a <code>.one</code> section, or a <code>.onepkg</code> notebook
-        package without sending it to a server.
+        with any linked <code>.cab</code> parts, without sending it to a server.
       </p>
       <input
         ref={input}
         className="visually-hidden"
         type="file"
-        accept=".one,.onepkg"
+        accept=".one,.onepkg,.cab"
+        multiple
         disabled={disabled}
-        onChange={selectFile}
+        onChange={selectFiles}
-        aria-label="Choose a OneNote file"
+        aria-label="Choose OneNote files"
       />
       <button
         type="button"
@@ -60,10 +61,10 @@ export function FileDropZone({ disabled = false, onFile }: FileDropZoneProps) {
         disabled={disabled}
         onClick={() => input.current?.click()}
       >
-        Choose OneNote file
+        Choose OneNote files
       </button>
       <span className="drop-zone__hint">
-        or drop one .one or .onepkg file here
+        or drop one .one, or one .onepkg with its .cab parts, here
       </span>
     </div>
   );

src/source-file.test.ts

@@ -0,0 +1,72 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  MAX_SOURCE_FILE_BYTES,
+  selectSourceFiles,
+  sourceKindFromFileName,
+} from './source-file.js';
+
+function source(name: string, size = 1) {
+  return { name, size };
+}
+
+describe('local source selection', () => {
+  it('accepts exactly one .one file', () => {
+    const section = source('Section.ONE');
+    expect(sourceKindFromFileName(section.name)).toBe('one');
+    expect(selectSourceFiles([section])).toEqual({
+      ok: true,
+      kind: 'one',
+      source: section,
+      cabinetParts: [],
+    });
+  });
+
+  it('finds one .onepkg and keeps CAB companions in selection order', () => {
+    const part3 = source('Notebook-3.CAB');
+    const primary = source('Notebook.OnePkg');
+    const part2 = source('Notebook-2.cab');
+    expect(selectSourceFiles([part3, primary, part2])).toEqual({
+      ok: true,
+      kind: 'onepkg',
+      source: primary,
+      cabinetParts: [part3, part2],
+    });
+  });
+
+  it('rejects duplicate names, unsupported files, and ambiguous primaries', () => {
+    expect(
+      selectSourceFiles([
+        source('Notebook.onepkg'),
+        source('Part.cab'),
+        source('PART.CAB'),
+      ])
+    ).toMatchObject({ ok: false, title: 'Duplicate file name' });
+    expect(selectSourceFiles([source('Notebook.zip')])).toMatchObject({
+      ok: false,
+      title: 'Unsupported file name',
+    });
+    expect(
+      selectSourceFiles([source('First.onepkg'), source('Second.onepkg')])
+    ).toMatchObject({ ok: false, title: 'Choose one OneNote source' });
+    expect(
+      selectSourceFiles([source('Section.one'), source('Notebook.onepkg')])
+    ).toMatchObject({ ok: false, title: 'Choose one OneNote source' });
+    expect(selectSourceFiles([source('Part.cab')])).toMatchObject({
+      ok: false,
+      title: 'Choose one OneNote source',
+    });
+  });
+
+  it('applies both per-file and aggregate 512 MiB limits', () => {
+    expect(
+      selectSourceFiles([source('Notebook.onepkg', MAX_SOURCE_FILE_BYTES + 1)])
+    ).toMatchObject({ ok: false, title: 'File is too large' });
+    expect(
+      selectSourceFiles([
+        source('Notebook.onepkg', 300 * 1024 * 1024),
+        source('Notebook-2.cab', 300 * 1024 * 1024),
+      ])
+    ).toMatchObject({ ok: false, title: 'Package set is too large' });
+  });
+});

src/source-file.ts

@@ -1,6 +1,33 @@
 import type { SourceKind } from './worker/onenote.client.js';
 
 export const MAX_SOURCE_FILE_BYTES = 512 * 1024 * 1024;
+export const MAX_SOURCE_PARTS = 256;
+
+export interface SourceFileDescriptor {
+  name: string;
+  size: number;
+}
+
+interface SourceFileSelectionFailure {
+  ok: false;
+  title: string;
+  message: string;
+}
+
+export type SourceFileSelection<T extends SourceFileDescriptor> =
+  | {
+      ok: true;
+      kind: 'one';
+      source: T;
+      cabinetParts: [];
+    }
+  | {
+      ok: true;
+      kind: 'onepkg';
+      source: T;
+      cabinetParts: T[];
+    }
+  | SourceFileSelectionFailure;
 
 export function sourceKindFromFileName(fileName: string): SourceKind | null {
   const normalized = fileName.toLocaleLowerCase('en-US');
@@ -8,3 +35,101 @@ export function sourceKindFromFileName(fileName: string): SourceKind | null {
   if (normalized.endsWith('.one')) return 'one';
   return null;
 }
+
+export function isCabinetPartFileName(fileName: string): boolean {
+  return fileName.toLocaleLowerCase('en-US').endsWith('.cab');
+}
+
+export function selectSourceFiles<T extends SourceFileDescriptor>(
+  files: readonly T[]
+): SourceFileSelection<T> {
+  if (files.length === 0) {
+    return invalidSelection();
+  }
+  if (files.length > MAX_SOURCE_PARTS) {
+    return {
+      ok: false,
+      title: 'Too many package parts',
+      message: `Choose at most ${MAX_SOURCE_PARTS} files for one cabinet set.`,
+    };
+  }
+
+  const sections: T[] = [];
+  const packages: T[] = [];
+  const cabinetParts: T[] = [];
+  for (const file of files) {
+    const kind = sourceKindFromFileName(file.name);
+    if (kind === 'one') sections.push(file);
+    else if (kind === 'onepkg') packages.push(file);
+    else if (isCabinetPartFileName(file.name)) cabinetParts.push(file);
+    else {
+      return {
+        ok: false,
+        title: 'Unsupported file name',
+        message:
+          'Choose one .one file, or one .onepkg file together with its .cab parts.',
+      };
+    }
+  }
+
+  const validSection =
+    sections.length === 1 && packages.length === 0 && cabinetParts.length === 0;
+  const validPackage = sections.length === 0 && packages.length === 1;
+  if (!validSection && !validPackage) return invalidSelection();
+
+  const seenNames = new Set<string>();
+  let totalSize = 0;
+  for (const file of files) {
+    const nameKey = file.name.normalize('NFC').toLocaleLowerCase('en-US');
+    if (seenNames.has(nameKey)) {
+      return {
+        ok: false,
+        title: 'Duplicate file name',
+        message: `The selection contains more than one file named ${file.name}.`,
+      };
+    }
+    seenNames.add(nameKey);
+    if (!Number.isSafeInteger(file.size) || file.size < 0) {
+      return {
+        ok: false,
+        title: 'Invalid file size',
+        message: `The browser reported an invalid size for ${file.name}.`,
+      };
+    }
+    if (file.size > MAX_SOURCE_FILE_BYTES) {
+      return {
+        ok: false,
+        title: 'File is too large',
+        message: `${file.name} exceeds the current 512 MiB safety limit.`,
+      };
+    }
+    totalSize += file.size;
+    if (!Number.isSafeInteger(totalSize) || totalSize > MAX_SOURCE_FILE_BYTES) {
+      return {
+        ok: false,
+        title: 'Package set is too large',
+        message:
+          'The selected .onepkg and .cab files exceed the combined 512 MiB safety limit.',
+      };
+    }
+  }
+
+  if (validSection) {
+    return { ok: true, kind: 'one', source: sections[0]!, cabinetParts: [] };
+  }
+  return {
+    ok: true,
+    kind: 'onepkg',
+    source: packages[0]!,
+    cabinetParts,
+  };
+}
+
+function invalidSelection(): SourceFileSelectionFailure {
+  return {
+    ok: false,
+    title: 'Choose one OneNote source',
+    message:
+      'Choose one .one file, or one .onepkg file together with its .cab parts.',
+  };
+}

src/worker/onenote.client.test.ts

@@ -29,20 +29,29 @@ class FakeWorker implements WorkerPort {
 }
 
 describe('OneNoteWorkerClient', () => {
-  it('uses the typed parse-onepkg protocol and transfers the source buffer', async () => {
+  it('transfers a ONEPKG and every named CAB companion', async () => {
     const worker = new FakeWorker();
     const client = new OneNoteWorkerClient(() => worker);
     const bytes = new ArrayBuffer(16);
-    const result = client.parseSource('onepkg', 'Notebook.onepkg', bytes);
+    const second = new ArrayBuffer(8);
+    const third = new ArrayBuffer(4);
+    const result = client.parseSource('onepkg', 'Notebook.onepkg', bytes, [
+      { fileName: 'part-3.cab', bytes: third },
+      { fileName: 'part-2.cab', bytes: second },
+    ]);
 
     expect(worker.lastMessage).toEqual(
       expect.objectContaining({
         type: 'parse-onepkg',
         fileName: 'Notebook.onepkg',
         bytes,
+        cabinetParts: [
+          { fileName: 'part-3.cab', bytes: third },
+          { fileName: 'part-2.cab', bytes: second },
+        ],
       })
     );
-    expect(worker.lastTransfer).toEqual([bytes]);
+    expect(worker.lastTransfer).toEqual([bytes, third, second]);
 
     const requestId =
       worker.lastMessage && 'requestId' in worker.lastMessage
@@ -143,7 +152,16 @@ describe('OneNoteWorkerClient', () => {
   it('rejects outstanding work when the worker is terminated', async () => {
     const worker = new FakeWorker();
     const client = new OneNoteWorkerClient(() => worker);
-    const result = client.parseSource('one', 'Section.one', new ArrayBuffer(8));
+    const bytes = new ArrayBuffer(8);
+    const result = client.parseSource('one', 'Section.one', bytes);
+
+    expect(worker.lastMessage).toEqual({
+      type: 'parse-one',
+      requestId: 'parse-1',
+      fileName: 'Section.one',
+      bytes,
+    });
+    expect(worker.lastTransfer).toEqual([bytes]);
 
     client.terminate();
 

src/worker/onenote.client.ts

@@ -4,6 +4,7 @@ import type {
   ParseWorkerResponse,
   ResourceWorkerResponse,
   WorkerRequest,
+  WorkerCabinetPart,
   WorkerFailure,
   WorkerResponse,
 } from './worker-protocol.js';
@@ -68,7 +69,8 @@ export class OneNoteWorkerClient {
   parseSource(
     kind: SourceKind,
     fileName: string,
-    bytes: ArrayBuffer
+    bytes: ArrayBuffer,
+    cabinetParts: readonly WorkerCabinetPart[] = []
   ): Promise<ParseWorkerResponse> {
     if (this.terminated) {
       return Promise.reject(
@@ -78,6 +80,14 @@ export class OneNoteWorkerClient {
         )
       );
     }
+    if (kind === 'one' && cabinetParts.length > 0) {
+      return Promise.reject(
+        new WorkerClientError(
+          'invalid-format',
+          'CAB companions can only be supplied with a .onepkg source.'
+        )
+      );
+    }
 
     const requestId = `parse-${++this.requestSequence}`;
     const request: ParseWorkerRequest = {
@@ -85,6 +95,9 @@ export class OneNoteWorkerClient {
       requestId,
       fileName,
       bytes,
+      ...(kind === 'onepkg' && cabinetParts.length > 0
+        ? { cabinetParts: [...cabinetParts] }
+        : {}),
     };
 
     return new Promise((resolve, reject) => {
@@ -92,7 +105,10 @@ export class OneNoteWorkerClient {
         resolve: (response) => resolve(response as ParseWorkerResponse),
         reject,
       });
-      this.worker.postMessage(request, [bytes]);
+      this.worker.postMessage(request, [
+        bytes,
+        ...cabinetParts.map((part) => part.bytes),
+      ]);
     });
   }
 

src/worker/onenote.worker.ts

@@ -3,6 +3,7 @@ import type { OneNoteResource } from '../onenote/one/content-model.js';
 import {
   failureFromUnknown,
   openPackageForWorker,
+  openPackageSetForWorker,
   openSectionForWorker,
   resourcePayload,
   workerPageKey,
@@ -59,10 +60,25 @@ async function handleRequest(data: WorkerRequest): Promise<void> {
     }
     case 'parse-onepkg':
       try {
-        const parsed = await openPackageForWorker(
+        const parsed =
-          new Uint8Array(data.bytes),
+          data.cabinetParts && data.cabinetParts.length > 0
-          data.fileName
+            ? await openPackageSetForWorker(
-        );
+                [
+                  {
+                    fileName: data.fileName,
+                    bytes: new Uint8Array(data.bytes),
+                  },
+                  ...data.cabinetParts.map((part) => ({
+                    fileName: part.fileName,
+                    bytes: new Uint8Array(part.bytes),
+                  })),
+                ],
+                data.fileName
+              )
+            : await openPackageForWorker(
+                new Uint8Array(data.bytes),
+                data.fileName
+              );
         const sessionId = createSession(parsed.pages, parsed.resources);
         workerScope.postMessage({
           type: 'package',

src/worker/parser-adapter.test.ts

@@ -5,6 +5,7 @@ import { describe, expect, it } from 'vitest';
 import {
   failureFromUnknown,
   openPackageForWorker,
+  openPackageSetForWorker,
   openSectionForWorker,
   resourcePayload,
   workerPageKey,
@@ -16,6 +17,15 @@ function fixtureBytes(path: string): Uint8Array {
   return Uint8Array.from(Buffer.from(encoded.replaceAll(/\s/gu, ''), 'base64'));
 }
 
+function multiCabPart(index: number) {
+  return {
+    fileName: `cabd_multi_basic_pt${index}.cab`,
+    bytes: fixtureBytes(
+      `../../tests/fixtures/libmspack-multi-basic-pt${index}.cab.b64`
+    ),
+  };
+}
+
 describe('worker parser adapter', () => {
   it('opens a real section and retains stable page identifiers', () => {
     const result = openSectionForWorker(
@@ -83,6 +93,24 @@ describe('worker parser adapter', () => {
     expect(result.resources).toBeInstanceOf(Map);
   });
 
+  it('opens named multi-cabinet package parts in arbitrary input order', async () => {
+    const parts = [4, 1, 5, 2, 3].map(multiCabPart);
+    const result = await openPackageSetForWorker(parts, 'Notebook.onepkg');
+
+    expect(result.notebook).toMatchObject({
+      sourceName: 'Notebook.onepkg',
+      sourceSize: parts.reduce((sum, part) => sum + part.bytes.length, 0),
+      entries: [
+        { path: 'test1.txt', kind: 'other' },
+        { path: 'test2.txt', kind: 'other' },
+        { path: 'test3.txt', kind: 'other' },
+      ],
+      sections: [],
+    });
+    expect(result.pages).toHaveLength(0);
+    expect(result.resources).toHaveLength(0);
+  });
+
   it('converts malformed section input into a controlled worker failure', () => {
     try {
       openSectionForWorker(new Uint8Array(20), 'broken.one');

src/worker/parser-adapter.ts

@@ -15,7 +15,13 @@ import type {
   OneNoteResource,
   OneNoteSectionContentModel,
 } from '../onenote/one/content-model.js';
-import { OnePkgError, openOneNotePackage } from '../onenote/onepkg/index.js';
+import {
+  OnePkgError,
+  openOneNotePackage,
+  openOneNotePackageSet,
+  type CabSetPart,
+  type OneNotePackageOpenOptions,
+} from '../onenote/onepkg/index.js';
 import type { WorkerFailure } from './worker-protocol.js';
 
 export interface ParsedWorkerSection {
@@ -135,12 +141,28 @@ export function openSectionForWorker(
 export async function openPackageForWorker(
   bytes: Uint8Array,
   sourceName: string
+): Promise<ParsedWorkerPackage> {
+  return openPackageSourceForWorker({ kind: 'single', bytes }, sourceName);
+}
+
+export async function openPackageSetForWorker(
+  parts: CabSetPart[],
+  sourceName: string
+): Promise<ParsedWorkerPackage> {
+  return openPackageSourceForWorker({ kind: 'set', parts }, sourceName);
+}
+
+async function openPackageSourceForWorker(
+  source:
+    | { kind: 'single'; bytes: Uint8Array }
+    | { kind: 'set'; parts: CabSetPart[] },
+  sourceName: string
 ): Promise<ParsedWorkerPackage> {
   const contentBySection = new Map<string, OneNoteSectionContentModel>();
-  const result = await openOneNotePackage(bytes, {
+  const options: OneNotePackageOpenOptions = {
     sourceName,
     cancellation: {
-      yield: () => new Promise((resolve) => setTimeout(resolve, 0)),
+      yield: () => new Promise<void>((resolve) => setTimeout(resolve, 0)),
     },
     parseSection: ({ sourceName: sectionName, bytes: sectionBytes }) => {
       try {
@@ -174,7 +196,11 @@ export async function openPackageForWorker(
         throw error;
       }
     },
-  });
+  };
+  const result =
+    source.kind === 'single'
+      ? await openOneNotePackage(source.bytes, options)
+      : await openOneNotePackageSet(source.parts, options);
 
   const pages = new Map<string, OneNotePageDto>();
   const resources = new Map<string, OneNoteResource>();

src/worker/worker-protocol.ts

@@ -5,6 +5,11 @@ import type {
   OneNoteSectionDto,
 } from '../onenote/model/dto.js';
 
+export interface WorkerCabinetPart {
+  fileName: string;
+  bytes: ArrayBuffer;
+}
+
 export type WorkerRequest =
   | {
       type: 'parse-one';
@@ -17,6 +22,7 @@ export type WorkerRequest =
       requestId: string;
       fileName: string;
       bytes: ArrayBuffer;
+      cabinetParts?: WorkerCabinetPart[];
     }
   | {
       type: 'get-page';