Names quak builds from server data fit in 255 bytes (closes #205)

The default names of `quak get`, `quak get-thumb`, `downloadFile` and `downloadThumbnail`, and the album folders of `backup-metadata`, could be over 255 bytes, which a file system refuses. `defaultFileName` and `shortenKeepingExtension` in `src/filename.ts` now cut such a name short, keeping its extension when it fits; a live photo's image and video get their own extension before the cut. A cut name never starts with a dot and is never a Windows device name. `--out` and `outPath` are kept as given. A `backup-metadata` folder keeps its `<id>-`. `safeExtension` gives `.bin` for an extension of more than 16 letters and digits, so a save path's name always fits.

Model: opus-5-5

test/cli/backup.test.ts

@@ -1795,12 +1795,11 @@ describe("backup album folders", () => {
         expect(readLedger(outDir).files["5"]).toMatchObject({ attempts: 1 });
     });
 
-    // The extensions of these titles leave no room for the ID, so each is cut
-    // short and the name before the ID keeps only the bytes that cut leaves
-    // over. File 1's extension is 303 bytes and is cut to 251, which leaves
-    // none. File 2's is 271 bytes and is cut to 250, since "€" takes three
-    // bytes, which leaves one, for the "a". Neither extension is only letters
-    // and digits, so both originals are saved with `.bin`, a name that fits.
+    // The extensions of these titles leave no room for the ID and the "a"
+    // before them, so each is cut short to 250 bytes, which leaves one, for
+    // the "a". File 1's extension is 303 bytes and file 2's 271. Neither
+    // extension is only letters and digits, so both originals are saved with
+    // `.bin`, a name that fits.
     it("cuts the extension of a title short when it leaves no room for the ID", async () => {
         const outDir = join(root, "backup");
         const lib = libraryOf([
@@ -1815,7 +1814,7 @@ describe("backup album folders", () => {
 
         const result = await runBackup(lib, { downloadDirectory: outDir });
 
-        const link = ` (1).${"L".repeat(250)}`;
+        const link = `a (1).${"L".repeat(249)}`;
         const link2 = `a (2).${"€".repeat(83)}`;
         expect(Buffer.byteLength(link)).toBe(255);
         expect(Buffer.byteLength(link2)).toBe(255);
@@ -1830,9 +1829,9 @@ describe("backup album folders", () => {
 
     // Files 1 and 3 share a title, so each gets its ID before the
     // extension. File 2's title is too long, and its extension leaves no
-    // room for the ID. Were the ID put at the end of file 2's title cut
-    // short, its link would have file 1's name, and the link made second
-    // would replace the first.
+    // room for the ID and the "x" before it. Were the ID put at the end of
+    // file 2's title cut short, its link would have file 1's name, and the
+    // link made second would replace the first.
     it("keeps names unique when a title's extension leaves no room for the ID", async () => {
         const outDir = join(root, "backup");
         const shared = `x.${"Q".repeat(245)} (2)`;
@@ -1852,8 +1851,8 @@ describe("backup album folders", () => {
         expect(result.failed).toBe(0);
         expect(tree(outDir)).toEqual([
             "Trip/",
-            `Trip/ (2).${"Q".repeat(250)} -> ${linkTo("2.bin")}`,
             `Trip/x (1).${"Q".repeat(245)} (2) -> ${linkTo("1.bin")}`,
+            `Trip/x (2).${"Q".repeat(249)} -> ${linkTo("2.bin")}`,
             `Trip/x (3).${"Q".repeat(245)} (2) -> ${linkTo("3.bin")}`,
             "Trip.json",
         ]);