Faster CI runs

ts/scripts/mocha-separator.ts

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+// Copyright 2025 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { spawnSync } from 'node:child_process';
+import { join } from 'node:path';
+
+const MOCHA = join(__dirname, '..', '..', 'node_modules', '.bin', 'mocha');
+const WORKER_COUNT = parseInt(process.env.WORKER_COUNT || '1', 10);
+const WORKER_INDEX = parseInt(process.env.WORKER_INDEX || '0', 10);
+
+const separator = process.argv.indexOf('--');
+if (separator === -1) {
+  throw new Error('Expected `--` separator between options and files');
+}
+
+const flags = process.argv.slice(2, separator);
+const files = process.argv.slice(separator + 1);
+
+const filteredFiles = files.filter((_file, index) => {
+  return index % WORKER_COUNT === WORKER_INDEX;
+});
+
+console.log(`Running on ${filteredFiles.length}/${files.length} of files`);
+
+spawnSync(MOCHA, [...flags, ...filteredFiles], {
+  stdio: 'inherit',
+});