feat: F5.5 large binary files as blobs on server F

From 16 KB a picture's or binary file's entry names its bytes by their
SHA-256 instead of holding them; the bytes are on F, content-addressed
(GET/POST /blobs with the session's grant, from the editor's origin, at
most 16 MiB). A document's blob side says where they are: the editor's
fetches and uploads, the room thread's asks F's main thread, and a start
waits for the ones asked for; without a side everything stays in the
document. Text stays Y.Text. A blob whose bytes are not there is never
written back empty. A blob F has not got yet is asked for again a few
times, and a running room reads late bytes.

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

packages/doc/src/files.ts

@@ -11,6 +11,7 @@
 import * as Y from 'yjs';
 import type { Id, VirtualFileContent, VirtualFileSystem } from '@mdg-filius/core';
 import { VirtualFileSystem as FileSystem } from '@mdg-filius/core';
+import { blobSha, blobSideOf } from './blobs.js';
 import { fileEntry, fileSystemOf, inOrder, ROOTS } from './projectDoc.js';
 
 export function sameBytes(left: Uint8Array, right: Uint8Array): boolean {
@@ -29,11 +30,21 @@ export function replaceText(text: Y.Text, next: string): void {
   if (next.length - start - end > 0) text.insert(start, next.slice(start, next.length - end));
 }
 
-/** Whether a document entry holds the content. */
+/**
+ * Whether a document entry holds the content (a blob by its bytes where they
+ * are here, else by its name).
+ */
 function holds(entry: Y.Map<unknown>, content: VirtualFileContent): boolean {
   if (entry.get('kind') !== content.kind) return false;
   if (content.kind === 'directory' || content.kind === 'text') return true;
-  return sameBytes(entry.get('data') as Uint8Array, content.data) && entry.get('mediaType') === content.mediaType;
+  if (entry.get('mediaType') !== content.mediaType) return false;
+  const blob = entry.get('blob');
+  if (typeof blob !== 'string') return sameBytes(entry.get('data') as Uint8Array, content.data);
+  const held = blobSideOf(entry.doc)?.bytes(blob);
+  // A blob whose bytes are not here was read as no bytes: written back so, that is no change (it would empty the file).
+  if (held === undefined && content.data.length === 0) return true;
+  if (entry.get('size') !== content.data.length) return false;
+  return held === undefined ? blobSha(content.data) === blob : sameBytes(held, content.data);
 }
 
 /**
@@ -42,6 +53,7 @@ function holds(entry: Y.Map<unknown>, content: VirtualFileContent): boolean {
  * longer the file system's (a renamed entry), numbered anew.
  */
 export function writeFiles(node: Y.Map<unknown>, fileSystem: VirtualFileSystem): void {
+  const blobs = blobSideOf(node.doc);
   let files = node.get('files') as Y.Map<Y.Map<unknown>> | undefined;
   const wanted: [string, VirtualFileContent][] = [];
   const walk = (folder: string): void => {
@@ -62,9 +74,9 @@ export function writeFiles(node: Y.Map<unknown>, fileSystem: VirtualFileSystem):
   for (const [path, content] of wanted) {
     const entry = files.get(path);
     if (entry === undefined) {
-      files.set(path, fileEntry(order++, content));
+      files.set(path, fileEntry(order++, content, blobs));
     } else if (!holds(entry, content)) {
-      files.set(path, fileEntry(entry.get('order') as number, content));
+      files.set(path, fileEntry(entry.get('order') as number, content, blobs));
     } else if (content.kind === 'text') {
       replaceText(entry.get('text') as Y.Text, content.text);
     }