A live photo's default names fit, and no cut name starts with a dot

`defaultFileName` in `src/filename.ts` now gives the name a file is saved
under when the caller gives no path, and `originalName`, `thumbnailName`,
`downloadFile` and `downloadThumbnail` all call it. For a live photo's image
and video it puts the part's own extension in before cutting the name short,
so those names fit too; a path from `--out` or `outPath` is kept as given.
`shortenKeepingExtension` keeps the first character before the extension,
cutting a long extension short to leave room for it, so a cut name no longer
starts with a dot. The backup's links for such a title change to match.
TODO.md names the open bug and describes what the code does.

Model: opus-5-5

test/cli/commands.test.ts

@@ -187,6 +187,9 @@ const FETCHED_BOTH_ALBUMS =
     "Fetched the files of 1 of 2 collections\n" +
     "Fetched the files of 2 of 2 collections\n";
 
+// The same for an account with one album.
+const FETCHED_ONE_ALBUM = "Fetched the files of 1 of 1 collections\n";
+
 // Collects everything written to it.
 class Output {
     text = "";
@@ -605,7 +608,7 @@ describe("names from an album name or a title over 255 bytes", () => {
         expect(Buffer.byteLength(name)).toBe(255);
         expect(code).toBe(0);
         expect(readdirSync(dir)).toEqual([name]);
-        expect(stderr.text).toBe(`7 bytes -> ${name}\n`);
+        expect(stderr.text).toBe(FETCHED_ONE_ALBUM + `7 bytes -> ${name}\n`);
     });
 
     it("get-thumb cuts the title short so that thumb_ and it fit in 255 bytes, and exits 0", async () => {
@@ -617,7 +620,7 @@ describe("names from an album name or a title over 255 bytes", () => {
         expect(Buffer.byteLength(name)).toBe(255);
         expect(code).toBe(0);
         expect(readdirSync(dir)).toEqual([name]);
-        expect(stderr.text).toBe(`3 bytes -> ${name}\n`);
+        expect(stderr.text).toBe(FETCHED_ONE_ALBUM + `3 bytes -> ${name}\n`);
     });
 
     it("backup-metadata cuts the album name short so that its folder's name fits in 255 bytes, and exits 0", async () => {
@@ -659,12 +662,12 @@ describe("names from an album name or a title over 255 bytes", () => {
 // one live photo, 300, downloaded through the real download layer
 // (test/live-photo.ts).
 describe("a live photo", () => {
-    // What `get` prints on stderr while its refresh fetches Vacation's files.
-    const FETCHED_ONE_ALBUM = "Fetched the files of 1 of 1 collections\n";
-
-    const livePhotoClient = async (image = IMAGE): Promise<Client> => {
+    const livePhotoClient = async (
+        image = IMAGE,
+        title = "IMG_0300.HEIC",
+    ): Promise<Client> => {
         const { file: live, body } = await asLivePhoto(
-            file(300, 1, "IMG_0300.HEIC"),
+            file(300, 1, title),
             livePhotoZip({ "image.heic": image, "video.mov": VIDEO }),
             livePhotoHash(image, VIDEO),
         );
@@ -712,6 +715,44 @@ describe("a live photo", () => {
         );
     });
 
+    // Run `get` without `--out` in a new directory for a live photo titled
+    // `title`, and return its exit code and the names it wrote.
+    const getInNewDirectory = async (
+        title: string,
+    ): Promise<{ code: number; names: string[] }> => {
+        const ctx = context(await livePhotoClient(IMAGE, title));
+        const dir = mkdtempSync(join(root, "cwd-"));
+        const previous = process.cwd();
+        process.chdir(dir);
+        try {
+            const code = await getCommand(ctx, "300", {});
+            return { code, names: readdirSync(dir).sort() };
+        } finally {
+            process.chdir(previous);
+        }
+    };
+    const imageName = `${"t".repeat(250)}.heic`;
+    const videoName = `${"t".repeat(251)}.mov`;
+
+    // The title fits, but ".heic" is one byte longer than ".jpg", so the
+    // image's name is cut short once its extension is in it.
+    it("get cuts its image's name short for a 255-byte title ending in .jpg, and exits 0", async () => {
+        const title = `${"t".repeat(251)}.jpg`;
+
+        const result = await getInNewDirectory(title);
+
+        expect(Buffer.byteLength(title)).toBe(255);
+        expect(Buffer.byteLength(imageName)).toBe(255);
+        expect(Buffer.byteLength(videoName)).toBe(255);
+        expect(result).toEqual({ code: 0, names: [imageName, videoName] });
+    });
+
+    it("get cuts the names of its image and video short for a 300-byte title with no extension, and exits 0", async () => {
+        const result = await getInNewDirectory("t".repeat(300));
+
+        expect(result).toEqual({ code: 0, names: [imageName, videoName] });
+    });
+
     it("get --out writes the image there and the video beside it", async () => {
         const out = join(root, "photo.jpg");
         const video = join(root, "photo.mov");