feat(worker): box-user script builders + username sanitizer

apps/agent-worker/src/runtime/box-user.ts

@@ -0,0 +1,75 @@
+// The per-box Linux user. Terminal sessions and agent turns exec as this user
+// instead of root (Claude Code refuses some operations as root, and a real
+// machine has a named user); sudo is passwordless until the user stores a
+// password, after which wheel membership makes sudo prompt for it.
+
+export const BOX_UID = 1000;
+
+const shellQuote = (value: string) => `'${value.replaceAll("'", "'\\''")}'`;
+
+// Linux-safe username derived from the Spoon username. The home path keeps
+// the Spoon username everywhere; only the passwd entry uses this.
+export const linuxUsername = (spoonUsername: string): string => {
+  const cleaned = spoonUsername
+    .toLowerCase()
+    .replaceAll(/[^a-z0-9_-]/g, '-')
+    .slice(0, 32);
+  if (!cleaned) return 'spoon';
+  return /^[a-z_]/.test(cleaned) ? cleaned : `u${cleaned}`.slice(0, 32);
+};
+
+// Idempotent root init: create the user at the (already mounted) home, grant
+// wheel, and chown the home ONCE (marker-guarded — later host-side writes are
+// repaired by targeted chowns, so a big home is never re-walked). `-o` allows
+// the uid even if the image ever gains a uid-1000 user; `-M` skips skeleton
+// copy since the mounted home persists across containers.
+export const buildBoxInitScript = (args: {
+  username: string;
+  home: string;
+}): string => {
+  const user = shellQuote(args.username);
+  const home = shellQuote(args.home);
+  const marker = shellQuote(`${args.home}/.spoon/chown-v1`);
+  return [
+    'set -e',
+    `if ! id -u ${user} >/dev/null 2>&1; then`,
+    `  useradd -u ${BOX_UID} -o -M -d ${home} -s /bin/bash ${user}`,
+    'fi',
+    `usermod -aG wheel ${user}`,
+    `if [ ! -f ${marker} ]; then`,
+    `  chown -R ${BOX_UID}:${BOX_UID} ${home}`,
+    `  mkdir -p "$(dirname ${marker})" && touch ${marker} && chown ${BOX_UID}:${BOX_UID} ${marker}`,
+    'fi',
+  ].join('\n');
+};
+
+// Sudo policy: NOPASSWD drop-in only while no password is stored; with a
+// password, wheel membership makes sudo prompt for it. The drop-in is staged
+// to a temp file and checked with `visudo -c` before install so a bad write
+// can never brick sudo.
+export const buildSudoPolicyScript = (args: {
+  username: string;
+  passwordSet: boolean;
+}): string => {
+  if (args.passwordSet) {
+    return 'rm -f /etc/sudoers.d/spoon-box';
+  }
+  const line = `${args.username} ALL=(ALL) NOPASSWD:ALL`;
+  return [
+    'set -e',
+    `printf '%s\\n' ${shellQuote(line)} > /etc/sudoers.d/spoon-box.tmp`,
+    'visudo -c -f /etc/sudoers.d/spoon-box.tmp',
+    'chmod 0440 /etc/sudoers.d/spoon-box.tmp',
+    'mv /etc/sudoers.d/spoon-box.tmp /etc/sudoers.d/spoon-box',
+  ].join('\n');
+};
+
+// `chpasswd` reads `user:password` from stdin, so the password never appears
+// in argv (visible in `ps`) or in a shell script body.
+export const CHPASSWD_COMMAND = ['chpasswd'];
+
+export const buildClearPasswordCommand = (username: string): string[] => [
+  'passwd',
+  '-d',
+  username,
+];

apps/agent-worker/tests/unit/box-user.test.ts

@@ -0,0 +1,79 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  buildBoxInitScript,
+  buildClearPasswordCommand,
+  buildSudoPolicyScript,
+  linuxUsername,
+} from '../../src/runtime/box-user';
+
+describe('linuxUsername', () => {
+  it('lowercases and passes through simple names', () => {
+    expect(linuxUsername('gabriel')).toBe('gabriel');
+    expect(linuxUsername('Gabriel')).toBe('gabriel');
+  });
+  it('replaces invalid characters with dashes', () => {
+    expect(linuxUsername('g@b r!el')).toBe('g-b-r-el');
+  });
+  it('prefixes names that do not start with [a-z_]', () => {
+    expect(linuxUsername('1337')).toBe('u1337');
+    expect(linuxUsername('-dash')).toBe('u-dash');
+  });
+  it('truncates to 32 chars and falls back to spoon', () => {
+    expect(linuxUsername('a'.repeat(40))).toHaveLength(32);
+    expect(linuxUsername('')).toBe('spoon');
+    expect(linuxUsername('@@@')).toBe('u---');
+  });
+});
+
+describe('buildBoxInitScript', () => {
+  const script = buildBoxInitScript({
+    username: 'gabriel',
+    home: '/home/Gabriel',
+  });
+  it('creates the user idempotently with uid 1000 at the given home', () => {
+    expect(script).toContain("id -u 'gabriel'");
+    expect(script).toContain('useradd');
+    expect(script).toContain('-u 1000');
+    expect(script).toContain("-d '/home/Gabriel'");
+    expect(script).toContain('-s /bin/bash');
+  });
+  it('adds wheel membership', () => {
+    expect(script).toContain("usermod -aG wheel 'gabriel'");
+  });
+  it('chowns the home once, guarded by the marker', () => {
+    expect(script).toContain('/home/Gabriel/.spoon/chown-v1');
+    expect(script).toContain("chown -R 1000:1000 '/home/Gabriel'");
+  });
+});
+
+describe('buildSudoPolicyScript', () => {
+  it('installs a visudo-validated NOPASSWD drop-in when no password is set', () => {
+    const script = buildSudoPolicyScript({
+      username: 'gabriel',
+      passwordSet: false,
+    });
+    expect(script).toContain('gabriel ALL=(ALL) NOPASSWD:ALL');
+    expect(script).toContain('visudo -c');
+    expect(script).toContain('/etc/sudoers.d/spoon-box');
+    expect(script).toContain('chmod 0440');
+  });
+  it('removes the drop-in when a password is set', () => {
+    const script = buildSudoPolicyScript({
+      username: 'gabriel',
+      passwordSet: true,
+    });
+    expect(script).toContain('rm -f /etc/sudoers.d/spoon-box');
+    expect(script).not.toContain('NOPASSWD');
+  });
+});
+
+describe('password commands', () => {
+  it('clears via passwd -d', () => {
+    expect(buildClearPasswordCommand('gabriel')).toEqual([
+      'passwd',
+      '-d',
+      'gabriel',
+    ]);
+  });
+});