feat(editor): a computer's files to and from the person's own files (F8.1)

Beside the dashboard only: Java's import window gets "Aus meinen Dateien"
(D4) — the dashboard is asked over the bridge for a file of at most Java's
150 000 bytes and hands its bytes over — and a file's menu gets "In meine
Dateien speichern" (D5), its bytes handed to the dashboard to save.

- Bridge: chooseFile/chosenFile and saveFile/savedFile, each question with
  its number; an answer from elsewhere, of another version, for no question
  or of the other kind is no answer.
- Whoever reads or finds the project frozen may save, not bring in.
- doc fileBytes: a text as UTF-8, a picture as it is, and "missing" while
  a blob's bytes have not come (read so, the file would be empty).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/doc/test/files.test.ts

@@ -5,7 +5,7 @@
 import { describe, expect, it } from 'vitest';
 import * as Y from 'yjs';
 import { saveTextAs, VirtualFileSystem } from '@mdg-filius/core';
-import { addDevice, changeFiles, emptyProject, fileText, nodeFiles, readFilesInto, ROOTS, writeProject } from '../src/index.js';
+import { addDevice, attachBlobs, BLOB_THRESHOLD_BYTES, changeFiles, emptyProject, fileBytes, fileText, memoryBlobSide, nodeFiles, readFilesInto, ROOTS, writeProject } from '../src/index.js';
 
 function setUp() {
   const doc = new Y.Doc();
@@ -56,6 +56,35 @@ describe("a device's files in the document", () => {
     expect(fileText(empty, 'pc', '/Notiz.txt')).toBeUndefined();
   });
 
+  it('give a file its bytes to take out: a text as UTF-8, a picture as it is, in any case; nothing for a folder or what is not there', () => {
+    const { doc } = setUp();
+    const picture = new Uint8Array([137, 80, 78, 71]);
+    changeFiles(doc, 'pc', 'me', (fileSystem) => {
+      fileSystem.writeTextFile('/Grüße.txt', 'Hallo Jörg\r\n');
+      fileSystem.createDirectory('/ordner');
+      fileSystem.writeImageFile('/ordner/Bild.png', picture, 'image/png');
+    });
+    expect(fileBytes(doc, 'pc', '/Grüße.txt')).toEqual({ name: 'Grüße.txt', bytes: new TextEncoder().encode('Hallo Jörg\r\n') });
+    expect(fileBytes(doc, 'pc', '/ORDNER/bild.PNG')).toEqual({ name: 'Bild.png', bytes: picture });
+    expect([fileBytes(doc, 'pc', '/ordner'), fileBytes(doc, 'pc', '/fehlt.txt'), fileBytes(doc, 'none', '/Grüße.txt')]).toEqual(['notFile', 'notFile', 'notFile']);
+  });
+
+  it("say a blob is missing until its bytes have come — read so, the file would be empty", () => {
+    const big = new Uint8Array(BLOB_THRESHOLD_BYTES + 5).map((_, index) => index % 251);
+    const { doc } = setUp();
+    attachBlobs(doc, memoryBlobSide());
+    changeFiles(doc, 'pc', 'me', (fileSystem) => fileSystem.writeBinaryFile('/gross.bin', big));
+    expect(fileBytes(doc, 'pc', '/gross.bin')).toEqual({ name: 'gross.bin', bytes: big });
+    // Another browser: the document, but not the bytes yet.
+    const there = new Y.Doc();
+    const side = memoryBlobSide();
+    attachBlobs(there, side);
+    Y.applyUpdate(there, Y.encodeStateAsUpdate(doc));
+    expect(fileBytes(there, 'pc', '/gross.bin')).toBe('missing');
+    side.arrived(new Map([[(doc.getMap<Y.Map<unknown>>(ROOTS.nodes).get('pc')!.get('files') as Y.Map<Y.Map<unknown>>).get('/gross.bin')!.get('blob') as string, big]]));
+    expect(fileBytes(there, 'pc', '/gross.bin')).toEqual({ name: 'gross.bin', bytes: big });
+  });
+
   it("go into a running engine's file system, what differs only: new ones after the others, changed ones in their place, gone ones removed", () => {
     const { doc } = setUp();
     changeFiles(doc, 'pc', 'me', (fileSystem) => {