fixup! diigo-cache: RSS in diigo's export shape, from cached items

compare-export.ts: the usage exit status is a named constant,
BAD_USAGE = 2, whose JSDoc cites the convention (Bash Reference Manual
§3.7.5); the manual just says "Exits 2 on bad usage".

Generated-by: Claude Opus 5.5

diigo-cache/scripts/compare-export.ts

@@ -8,9 +8,7 @@
  * the export, keyed on link: title, tags, description, highlights and
  * sticky notes. Prints counts to stdout; writes <out-dir>/from-cache.rss
  * and <out-dir>/report.json (mismatched links, by category). Exits 2 on
- * bad usage, the shell's convention.
- *
- * @see https://www.gnu.org/software/bash/manual/html_node/Exit-Status.html
+ * bad usage.
  */
 import * as nodeFs from "node:fs/promises";
 import { basename, join } from "node:path";
@@ -19,6 +17,14 @@ import { itemDescription, toRss } from "../src/rss.ts";
 
 type Item = Record<string, unknown>;
 
+/**
+ * the exit status for incorrect usage (invalid options, missing
+ * arguments): the shell's convention
+ *
+ * @see https://www.gnu.org/software/bash/manual/html_node/Exit-Status.html
+ */
+const BAD_USAGE = 2;
+
 /** one export item, as read */
 type Exported = { title: string; link: string; description: string };
 
@@ -142,7 +148,7 @@ export async function main(
 	const [dbPath, exportPath, outPath] = argv;
 	if (!dbPath || !exportPath || !outPath) {
 		stderr.write("usage: node scripts/compare-export.ts <cache.sqlite> <export.xml> <out-dir>\n");
-		return exit(2);
+		return exit(BAD_USAGE);
 	}
 	const cache = cacheItems(connect(dbPath));
 	const out = outDir(fs, outPath);