Decrypt and persist all file metadata layers

Extends RawEnteFile and EnteFile with optional magicMetadata and
pubMagicMetadata fields. Both are secretstream blobs under the file
key, decrypted to arbitrary JSON (Record<string, unknown>).

pubMagicMetadata carries ML-derived data from the Ente clients:
camera make/model, image dimensions, datetime with timezone offset,
and (when present) captions, editedName, face labels, keywords.

magicMetadata carries private mutable fields like visibility.

Backup now writes per-file JSON at originals/<fileID>.json containing
all three metadata layers (basic + magic + pubMagic).

Live-tested: all 11 files in the dev account have pubMagicMetadata
with SONY DSC-RX1RM3 camera info and 3000x2000 dimensions.

src/backup.ts

@@ -116,6 +116,24 @@ export const runBackup = async (
                 }
             }
 
+            // Write per-file metadata JSON alongside the original
+            const metaJsonPath = join(originalsDir, `${file.id}.json`);
+            if (!existsSync(metaJsonPath)) {
+                const fileMeta: Record<string, unknown> = {
+                    id: file.id,
+                    collectionID: file.collectionID,
+                    ownerID: file.ownerID,
+                    metadata: file.metadata,
+                };
+                if (file.magicMetadata) {
+                    fileMeta.magicMetadata = file.magicMetadata;
+                }
+                if (file.pubMagicMetadata) {
+                    fileMeta.pubMagicMetadata = file.pubMagicMetadata;
+                }
+                writeFileSync(metaJsonPath, JSON.stringify(fileMeta, null, 2));
+            }
+
             if (!existsSync(linkPath) && existsSync(origPath)) {
                 const target = relative(colDir, origPath);
                 symlinkSync(target, linkPath);

src/model/decrypt.ts

@@ -7,6 +7,7 @@ import type {
     FileType,
     RawCollection,
     RawEnteFile,
+    RawMagicMetadata,
 } from "./types.js";
 
 const KNOWN_COLLECTION_TYPES = new Set([
@@ -88,14 +89,32 @@ export const decryptFile = (
         hash: metadataJSON.hash,
     };
 
+    const magicMetadata = decryptMagicMetadata(raw.magicMetadata, key);
+    const pubMagicMetadata = decryptMagicMetadata(raw.pubMagicMetadata, key);
+
     return {
         id: raw.id,
         collectionID: raw.collectionID,
         ownerID: raw.ownerID,
         key,
         metadata,
+        magicMetadata,
+        pubMagicMetadata,
         file: { decryptionHeader: raw.file.decryptionHeader },
         thumbnail: { decryptionHeader: raw.thumbnail.decryptionHeader },
         updationTime: raw.updationTime,
     };
 };
+
+const decryptMagicMetadata = (
+    raw: RawMagicMetadata | undefined,
+    key: Uint8Array,
+): Record<string, unknown> | undefined => {
+    if (!raw?.data || !raw?.header) return undefined;
+    const bytes = decryptBlob(
+        fromBase64(raw.data),
+        fromBase64(raw.header),
+        key,
+    );
+    return JSON.parse(new TextDecoder().decode(bytes));
+};

src/model/index.ts

@@ -9,4 +9,5 @@ export type {
     Microseconds,
     RawCollection,
     RawEnteFile,
+    RawMagicMetadata,
 } from "./types.js";

src/model/types.ts

@@ -40,6 +40,8 @@ export interface EnteFile {
     ownerID: number;
     key: Uint8Array;
     metadata: FileMetadata;
+    magicMetadata?: Record<string, unknown>;
+    pubMagicMetadata?: Record<string, unknown>;
     file: FileBlob;
     thumbnail: FileBlob;
     updationTime: Microseconds;
@@ -59,6 +61,13 @@ export interface RawCollection {
     isDeleted?: boolean;
 }
 
+export interface RawMagicMetadata {
+    version: number;
+    count: number;
+    data: string;
+    header: string;
+}
+
 export interface RawEnteFile {
     id: number;
     collectionID: number;
@@ -66,6 +75,8 @@ export interface RawEnteFile {
     encryptedKey: string;
     keyDecryptionNonce: string;
     metadata: { encryptedData: string; decryptionHeader: string };
+    magicMetadata?: RawMagicMetadata;
+    pubMagicMetadata?: RawMagicMetadata;
     info?: { fileSize?: number; thumbSize?: number };
     file: { decryptionHeader: string };
     thumbnail: { decryptionHeader: string };