Carry file size, thumbnail size, and deletion flag through decryptFile (closes #37)

Foundation unit for the cache/API design. Three fields arrived on the wire
but decryptFile dropped them:

- `file.size` from `info.fileSize` and `thumbnail.size` from `info.thumbSize`,
  left `undefined` when the server omits `info`.
- `isDeleted` carried from the diff row onto `EnteFile`.

No caller change: `listFiles` still filters deleted rows before decrypt, so no
deleted row reaches decryptFile here. Surfacing a deleted file through
decryption belongs to the enumeration unit, issue 38, where the return shape
can be designed around where such a row actually flows.

Model: opus-4-8

test/model/decrypt.test.ts

@@ -145,7 +145,12 @@ const buildSharedRawCollection = (
 
 const buildRawFile = (
     collectionKey: Uint8Array,
-    opts?: { title?: string; fileType?: number; creationTime?: number },
+    opts?: {
+        title?: string;
+        fileType?: number;
+        creationTime?: number;
+        info?: { fileSize?: number; thumbSize?: number };
+    },
 ): RawEnteFile => {
     const fileKey = sodium.crypto_secretbox_keygen();
     const { ciphertext: encFileKey, nonce: fileKeyNonce } = secretboxEncrypt(
@@ -186,6 +191,7 @@ const buildRawFile = (
         },
         file: { decryptionHeader: toBase64(sodium.randombytes_buf(24)) },
         thumbnail: { decryptionHeader: toBase64(sodium.randombytes_buf(24)) },
+        info: opts?.info,
         updationTime: 1700000000000000,
     };
 };
@@ -357,4 +363,47 @@ describe("model.decryptFile", () => {
 
         expect(() => decryptFile(raw, wrongKey)).toThrow();
     });
+
+    it("carries the file and thumbnail byte sizes from info", () => {
+        // The server reports the encrypted-blob sizes in `info`; the cache
+        // needs them without a HEAD request, so decryptFile must copy them
+        // onto the file and thumbnail blobs.
+        const masterKey = sodium.crypto_secretbox_keygen();
+        const { collectionKey } = buildRawCollection(masterKey);
+        const raw = buildRawFile(collectionKey, {
+            info: { fileSize: 4096, thumbSize: 512 },
+        });
+
+        const file = decryptFile(raw, collectionKey);
+
+        expect(file.file.size).toBe(4096);
+        expect(file.thumbnail.size).toBe(512);
+    });
+
+    it("leaves the sizes undefined when the server omits info", () => {
+        // Older files predate the info field; the sizes must stay undefined
+        // rather than become 0, so callers can tell "unknown" from "empty".
+        const masterKey = sodium.crypto_secretbox_keygen();
+        const { collectionKey } = buildRawCollection(masterKey);
+        const raw = buildRawFile(collectionKey);
+        expect(raw.info).toBeUndefined();
+
+        const file = decryptFile(raw, collectionKey);
+
+        expect(file.file.size).toBeUndefined();
+        expect(file.thumbnail.size).toBeUndefined();
+    });
+
+    it("carries the deletion flag from the diff row", () => {
+        // The diff marks a deleted row with isDeleted; decryptFile copies it
+        // onto the file so a caller can tell a deleted row from a live one.
+        const masterKey = sodium.crypto_secretbox_keygen();
+        const { collectionKey } = buildRawCollection(masterKey);
+        const raw = buildRawFile(collectionKey);
+        raw.isDeleted = true;
+
+        const file = decryptFile(raw, collectionKey);
+
+        expect(file.isDeleted).toBe(true);
+    });
 });