diff --git a/package.json b/package.json
index 9a28beee..61942702 100644
--- a/package.json
+++ b/package.json
@@ -39,7 +39,7 @@
   },
   "scripts": {
     "build": "tsc -p tsconfig.build.json && node ./scripts/copy-renderer-assets.mjs",
-    "clean": "rimraf coverage dist *.tsbuildinfo",
+    "clean": "rimraf coverage dist .tsconfig.tsbuildinfo .tsconfig.build.tsbuildinfo",
     "cli": "tsx src/cli/main.ts",
     "doctor": "tsx src/cli/main.ts doctor",
     "format": "oxfmt . --write",
diff --git a/test/unit/tools/clean-script.test.ts b/test/unit/tools/clean-script.test.ts
new file mode 100644
index 00000000..1be30063
--- /dev/null
+++ b/test/unit/tools/clean-script.test.ts
@@ -0,0 +1,77 @@
+import { execSync } from 'node:child_process';
+import { existsSync, readFileSync } from 'node:fs';
+import { mkdir, mkdtemp, realpath, rm, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { delimiter, join, resolve } from 'node:path';
+
+import { afterEach, describe, expect, it } from 'vitest';
+
+const repoRoot = resolve(import.meta.dirname, '../../..');
+const tempDirs: string[] = [];
+
+afterEach(async () => {
+  await Promise.all(
+    tempDirs.splice(0).map((dir) => rm(dir, { recursive: true, force: true })),
+  );
+});
+
+function buildInfoFiles(): string[] {
+  return ['tsconfig.json', 'tsconfig.build.json'].map((name) => {
+    const text = readFileSync(join(repoRoot, name), 'utf8');
+    const file = /"tsBuildInfoFile":\s*"([^"]+)"/.exec(text)?.[1];
+    if (file === undefined) {
+      throw new Error(`${name} names no tsBuildInfoFile`);
+    }
+    return file;
+  });
+}
+
+describe('npm run clean', () => {
+  // A build info file that survives `clean` makes the next `tsc -p` build
+  // skip its output, so `clean` then `build` would leave dist/ empty.
+  it('removes dist, coverage and every build info file the tsconfigs name, and nothing else', async () => {
+    const pkg = JSON.parse(
+      readFileSync(join(repoRoot, 'package.json'), 'utf8'),
+    ) as { scripts: Record<string, string> };
+    const script = pkg.scripts.clean;
+    if (script === undefined) {
+      throw new Error('package.json has no clean script');
+    }
+
+    const dir = await realpath(
+      await mkdtemp(join(tmpdir(), 'agent-tty-clean-')),
+    );
+    tempDirs.push(dir);
+    const kept = ['package.json', 'src/cli/main.ts', 'visible.tsbuildinfo'];
+    const targets = [
+      'dist/cli/main.js',
+      'coverage/index.html',
+      ...buildInfoFiles(),
+      ...kept,
+    ];
+    for (const target of targets) {
+      await mkdir(join(dir, target, '..'), { recursive: true });
+      await writeFile(join(dir, target), 'stale');
+    }
+
+    // npm runs scripts through /bin/sh, or cmd.exe on Windows; execSync
+    // picks the same shell. The variable can be spelled Path or PATH, and a
+    // shell can carry both, so prepend the bin folder to each spelling.
+    const bin = join(repoRoot, 'node_modules', '.bin');
+    const env: NodeJS.ProcessEnv = { ...process.env };
+    const pathKeys = Object.keys(env).filter(
+      (key) => key.toUpperCase() === 'PATH',
+    );
+    for (const key of pathKeys.length > 0 ? pathKeys : ['PATH']) {
+      env[key] = `${bin}${delimiter}${env[key] ?? ''}`;
+    }
+    execSync(script, { cwd: dir, env, stdio: 'pipe' });
+
+    for (const target of ['dist', 'coverage', ...buildInfoFiles()]) {
+      expect(existsSync(join(dir, target)), `${target} removed`).toBe(false);
+    }
+    for (const target of kept) {
+      expect(existsSync(join(dir, target)), `${target} kept`).toBe(true);
+    }
+  });
+});