diff --git a/dashcaddy-api/__tests__/license-keygen.test.js b/dashcaddy-api/__tests__/license-keygen.test.js
new file mode 100644
index 0000000..77d1b9a
--- /dev/null
+++ b/dashcaddy-api/__tests__/license-keygen.test.js
@@ -0,0 +1,460 @@
+/**
+ * Tests for dashcaddy-api/license-keygen.js
+ *
+ * Covers the programmatic API used by the Stripe webhook bridge and the
+ * on-disk counter allocator. The CLI path is exercised through the
+ * dedicated CLI regression describe block at the bottom of this file.
+ *
+ *   - module.exports shape: verifyCode, parseCode, generateCode,
+ *     generateCodes, loadSecret, VALID_DURATIONS, VERSION
+ *   - generateCodes() validation: secret, duration, count
+ *   - generateCodes() counter allocator: init, increment, override via
+ *     startId, override via counterFile, atomic .tmp shape
+ *   - generateCodes() monotonic counter: 100-call ordering, range checks
+ *   - loadSecret() success and missing-file error
+ *   - generateCode() round-trip: codes verify back via verifyCode()
+ *   - CLI integration: omitted --start-id uses auto-counter, explicit
+ *     --start-id skips counter write, --lifetime/--duration mutual exclusion
+ */
+
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const os = require('os');
+const { execFileSync } = require('child_process');
+
+const keygen = require('../license-keygen');
+const {
+  verifyCode,
+  parseCode,
+  generateCode,
+  generateCodes,
+  loadSecret,
+  VALID_DURATIONS,
+  VERSION,
+} = keygen;
+
+function _tmpDir(prefix) {
+  return fs.mkdtempSync(path.join(os.tmpdir(), `dashcaddy-${prefix}-`));
+}
+
+function _cleanup(dir) {
+  try { fs.rmSync(dir, { recursive: true, force: true }); } catch (_) { /* best effort */ }
+}
+
+const TEST_SECRET = 'a'.repeat(64); // 32 bytes hex
+
+// ── Public surface ──────────────────────────────────────────────────────────
+
+describe('license-keygen: module.exports', () => {
+  test('exports verifyCode, parseCode, generateCode, generateCodes, loadSecret, VALID_DURATIONS, VERSION', () => {
+    expect(typeof verifyCode).toBe('function');
+    expect(typeof parseCode).toBe('function');
+    expect(typeof generateCode).toBe('function');
+    expect(typeof generateCodes).toBe('function');
+    expect(typeof loadSecret).toBe('function');
+    expect(Array.isArray(VALID_DURATIONS)).toBe(true);
+    expect(VALID_DURATIONS).toEqual([30, 90, 180, 365]);
+    expect(VERSION).toBe(1);
+  });
+});
+
+// ── generateCode / parseCode / verifyCode round-trip ────────────────────────
+
+describe('license-keygen: generateCode round-trip', () => {
+  test('generated code verifies back via verifyCode()', () => {
+    const code = generateCode(TEST_SECRET, 90, 42);
+    expect(code).toMatch(/^DC-([0-9A-Z]{5})(-[0-9A-Z]{5}){4}$/);
+    const result = verifyCode(TEST_SECRET, code);
+    expect(result.valid).toBe(true);
+    expect(result.durationDays).toBe(90);
+    expect(result.codeId).toBe(42);
+  });
+
+  test('verifyCode rejects a code from a different secret', () => {
+    const code = generateCode(TEST_SECRET, 30, 1);
+    const result = verifyCode('b'.repeat(64), code);
+    expect(result.valid).toBe(false);
+    expect(result.reason).toMatch(/signature/i);
+  });
+
+  test('parseCode returns version, duration, codeId, timestamp', () => {
+    const code = generateCode(TEST_SECRET, 365, 9999);
+    const parsed = parseCode(code);
+    expect(parsed.version).toBe(VERSION);
+    expect(parsed.durationDays).toBe(365);
+    expect(parsed.codeId).toBe(9999);
+    expect(typeof parsed.createdTs).toBe('number');
+  });
+});
+
+// ── generateCodes: validation ───────────────────────────────────────────────
+
+describe('license-keygen: generateCodes validation', () => {
+  test('throws on missing secret', () => {
+    expect(() => generateCodes({ secret: '', durationDays: 30 })).toThrow(/secret is required/);
+    expect(() => generateCodes({ secret: 123, durationDays: 30 })).toThrow(/secret is required/);
+    expect(() => generateCodes({ durationDays: 30 })).toThrow(/secret is required/);
+  });
+
+  test('throws on invalid duration', () => {
+    expect(() => generateCodes({ secret: TEST_SECRET, durationDays: 7 })).toThrow(/invalid duration/);
+    expect(() => generateCodes({ secret: TEST_SECRET, durationDays: 31 })).toThrow(/invalid duration/);
+    expect(() => generateCodes({ secret: TEST_SECRET, durationDays: -1 })).toThrow(/invalid duration/);
+  });
+
+  test('accepts LIFETIME (durationDays: 0)', () => {
+    const tmp = _tmpDir('kg-lifetime');
+    try {
+      const codes = generateCodes({
+        secret: TEST_SECRET,
+        durationDays: 0,
+        counterFile: path.join(tmp, '.counter'),
+      });
+      expect(codes).toHaveLength(1);
+      expect(codes[0].durationDays).toBe(0);
+    } finally { _cleanup(tmp); }
+  });
+
+  test('throws on invalid count', () => {
+    expect(() => generateCodes({ secret: TEST_SECRET, durationDays: 30, count: 0 })).toThrow(/invalid count/);
+    expect(() => generateCodes({ secret: TEST_SECRET, durationDays: 30, count: -1 })).toThrow(/invalid count/);
+    expect(() => generateCodes({ secret: TEST_SECRET, durationDays: 30, count: 10001 })).toThrow(/invalid count/);
+    expect(() => generateCodes({ secret: TEST_SECRET, durationDays: 30, count: 1.5 })).toThrow(/invalid count/);
+  });
+});
+
+// ── generateCodes: counter allocator ────────────────────────────────────────
+
+describe('license-keygen: generateCodes counter', () => {
+  let tmp;
+  beforeEach(() => { tmp = _tmpDir('kg-counter'); });
+  afterEach(() => { _cleanup(tmp); });
+
+  test('initializes counter at 1 when file is missing', () => {
+    const codes = generateCodes({
+      secret: TEST_SECRET,
+      durationDays: 30,
+      counterFile: path.join(tmp, '.counter'),
+    });
+    expect(codes[0].codeId).toBe(1);
+    expect(fs.readFileSync(path.join(tmp, '.counter'), 'utf8').trim()).toBe('1');
+  });
+
+  test('increments counter on subsequent calls', () => {
+    const counterFile = path.join(tmp, '.counter');
+    for (let i = 1; i <= 3; i++) {
+      const codes = generateCodes({
+        secret: TEST_SECRET,
+        durationDays: 30,
+        counterFile,
+      });
+      expect(codes[0].codeId).toBe(i);
+    }
+    expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe('3');
+  });
+
+  test('respects startId override and does NOT touch the counter file', () => {
+    const counterFile = path.join(tmp, '.counter');
+    fs.writeFileSync(counterFile, '100');
+    const codes = generateCodes({
+      secret: TEST_SECRET,
+      durationDays: 30,
+      count: 3,
+      startId: 500,
+      counterFile,
+    });
+    expect(codes.map(c => c.codeId)).toEqual([500, 501, 502]);
+    // Counter file unchanged — overrideStartId path skips the write.
+    expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe('100');
+  });
+
+  test('no leftover .tmp files after a successful call', () => {
+    const counterFile = path.join(tmp, '.counter');
+    generateCodes({ secret: TEST_SECRET, durationDays: 30, counterFile });
+    const entries = fs.readdirSync(tmp);
+    expect(entries.filter(e => e.includes('.tmp'))).toEqual([]);
+  });
+
+  test('counter file uses per-call unique tmp suffix (no .tmp collisions)', () => {
+    const counterFile = path.join(tmp, '.counter');
+    const origWrite = fs.writeFileSync;
+    const tmpNames = [];
+    fs.writeFileSync = (p, data, opts) => {
+      if (typeof p === 'string' && p.startsWith(counterFile) && p.includes('.tmp')) {
+        tmpNames.push(p);
+      }
+      return origWrite.call(fs, p, data, opts);
+    };
+    try {
+      generateCodes({ secret: TEST_SECRET, durationDays: 30, counterFile });
+      generateCodes({ secret: TEST_SECRET, durationDays: 30, counterFile });
+      expect(tmpNames).toHaveLength(2);
+      expect(new Set(tmpNames).size).toBe(2);
+    } finally {
+      fs.writeFileSync = origWrite;
+    }
+  });
+});
+
+// ── generateCodes: monotonic counter ────────────────────────────────────────
+//
+// generateCodes() is synchronous. Node's single-threaded event loop means
+// two synchronous calls cannot interleave, so the counter is monotonically
+// incremented without any explicit locking. The atomic write helper
+// protects against process crashes between writeFileSync and renameSync.
+// These tests verify that ordering and atomicity hold across many calls.
+
+describe('license-keygen: generateCodes monotonic counter', () => {
+  let tmp;
+  beforeEach(() => { tmp = _tmpDir('kg-mono'); });
+  afterEach(() => { _cleanup(tmp); });
+
+  test('100 sequential calls produce 100 unique codeIds in monotonic order', () => {
+    const counterFile = path.join(tmp, '.counter');
+    const codes = [];
+    for (let i = 0; i < 100; i++) {
+      codes.push(generateCodes({
+        secret: TEST_SECRET,
+        durationDays: 30,
+        counterFile,
+      })[0]);
+    }
+    const ids = codes.map(c => c.codeId);
+    expect(ids).toHaveLength(100);
+    expect(new Set(ids).size).toBe(100);
+    for (let i = 1; i < ids.length; i++) {
+      expect(ids[i]).toBe(ids[i - 1] + 1);
+    }
+    expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe('100');
+  });
+
+  test('100 sequential calls each requesting 5 codes produce 500 unique IDs', () => {
+    const counterFile = path.join(tmp, '.counter');
+    const batches = [];
+    for (let i = 0; i < 100; i++) {
+      batches.push(generateCodes({
+        secret: TEST_SECRET,
+        durationDays: 30,
+        count: 5,
+        counterFile,
+      }));
+    }
+    const allIds = batches.flat().map(c => c.codeId);
+    expect(allIds).toHaveLength(500);
+    expect(new Set(allIds).size).toBe(500);
+    batches.forEach((batch, i) => {
+      const start = i * 5 + 1;
+      expect(batch.map(c => c.codeId)).toEqual([start, start + 1, start + 2, start + 3, start + 4]);
+    });
+    expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe('500');
+  });
+
+  test('startId override is range-checked (negative throws)', () => {
+    expect(() => generateCodes({
+      secret: TEST_SECRET,
+      durationDays: 30,
+      startId: -1,
+      counterFile: path.join(tmp, '.counter'),
+    })).toThrow(/out of range/);
+  });
+
+  test('startId override is range-checked (over 32-bit throws)', () => {
+    expect(() => generateCodes({
+      secret: TEST_SECRET,
+      durationDays: 30,
+      startId: 0x100000000,
+      counterFile: path.join(tmp, '.counter'),
+    })).toThrow(/out of range/);
+  });
+
+  test('startId override is rejected for non-integer values', () => {
+    // Codex round 2: Number.isInteger(overrideStartId) returned false for
+    // floats/NaN/null/strings, silently falling through to auto-counter.
+    // The Object.prototype.hasOwnProperty check above fixes the dispatch.
+    const counterFile = path.join(tmp, '.counter');
+    fs.writeFileSync(counterFile, '99');
+    for (const bad of [1.5, NaN, null, '100', undefined, false]) {
+      const prevValue = fs.readFileSync(counterFile, 'utf8').trim();
+      expect(() => generateCodes({
+        secret: TEST_SECRET,
+        durationDays: 30,
+        startId: bad,
+        counterFile,
+      })).toThrow(/out of range|non-integer/);
+      // Counter file must NOT be touched when the call throws.
+      expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe(prevValue);
+    }
+  });
+
+  test('count that would push codeId past 32-bit throws', () => {
+    const counterFile = path.join(tmp, '.counter');
+    fs.writeFileSync(counterFile, String(0xFFFFFFFF - 5));
+    expect(() => generateCodes({
+      secret: TEST_SECRET,
+      durationDays: 30,
+      count: 10,
+      counterFile,
+    })).toThrow(/32-bit limit/);
+  });
+});
+
+// ── generateCodes: counterFile override ─────────────────────────────────────
+
+describe('license-keygen: generateCodes counterFile override', () => {
+  let tmp;
+  beforeEach(() => { tmp = _tmpDir('kg-cf'); });
+  afterEach(() => { _cleanup(tmp); });
+
+  test('counterFile option overrides LICENSE_COUNTER_FILE env', () => {
+    const cf = path.join(tmp, '.counter');
+    const prev = process.env.LICENSE_COUNTER_FILE;
+    try {
+      process.env.LICENSE_COUNTER_FILE = path.join(tmp, 'env-counter');
+      generateCodes({ secret: TEST_SECRET, durationDays: 30, counterFile: cf });
+      expect(fs.existsSync(cf)).toBe(true);
+      expect(fs.existsSync(path.join(tmp, 'env-counter'))).toBe(false);
+    } finally {
+      if (prev === undefined) delete process.env.LICENSE_COUNTER_FILE;
+      else process.env.LICENSE_COUNTER_FILE = prev;
+    }
+  });
+
+  test('LICENSE_COUNTER_FILE env overrides the default __dirname counter', () => {
+    const tmpForEnv = _tmpDir('kg-env');
+    try {
+      const target = path.join(tmpForEnv, 'env-counter');
+      const prev = process.env.LICENSE_COUNTER_FILE;
+      process.env.LICENSE_COUNTER_FILE = target;
+      try {
+        const codes = generateCodes({ secret: TEST_SECRET, durationDays: 30 });
+        expect(codes[0].codeId).toBeLessThanOrEqual(1); // fresh env
+        expect(fs.existsSync(target)).toBe(true);
+      } finally {
+        if (prev === undefined) delete process.env.LICENSE_COUNTER_FILE;
+        else process.env.LICENSE_COUNTER_FILE = prev;
+      }
+    } finally { _cleanup(tmpForEnv); }
+  });
+});
+
+// ── loadSecret ──────────────────────────────────────────────────────────────
+
+describe('license-keygen: loadSecret', () => {
+  let tmp;
+  beforeEach(() => { tmp = _tmpDir('kg-secret'); });
+  afterEach(() => { _cleanup(tmp); });
+
+  test('returns trimmed contents of an existing secret file', () => {
+    const file = path.join(tmp, '.license-secret');
+    fs.writeFileSync(file, '  abc123  \n');
+    expect(loadSecret(file)).toBe('abc123');
+  });
+
+  test('throws on missing file with helpful message', () => {
+    const file = path.join(tmp, 'does-not-exist');
+    expect(() => loadSecret(file)).toThrow(/not found/i);
+    expect(() => loadSecret(file)).toThrow(/--init-secret/i);
+  });
+});
+
+// ── generateCodes: failure modes ────────────────────────────────────────────
+
+describe('license-keygen: generateCodes failure modes', () => {
+  let tmp;
+  beforeEach(() => { tmp = _tmpDir('kg-fail'); });
+  afterEach(() => { _cleanup(tmp); });
+
+  test('throws when counter file exists but contains non-numeric data', () => {
+    const counterFile = path.join(tmp, '.counter');
+    fs.writeFileSync(counterFile, 'not-a-number');
+    expect(() =>
+      generateCodes({ secret: TEST_SECRET, durationDays: 30, counterFile }),
+    ).toThrow(/non-numeric/);
+  });
+});
+
+// ── CLI regression: spawn the real binary and verify argument handling ───────
+//
+// Codex round 4 caught a regression: main() always passed
+// `startId: overrideStartId` to generateCodes(), even when --start-id was
+// omitted. The new hasOwnProperty-based validation then rejected the call
+// because startId was an explicit (undefined) value. The fix is to omit
+// the startId property from the options object when --start-id is absent.
+// These tests exercise the actual CLI binary to make sure the local fix
+// wires up correctly.
+
+const KEYGEN_BIN = path.resolve(__dirname, '..', 'license-keygen.js');
+
+function _runCli(args, env) {
+  return execFileSync('node', [KEYGEN_BIN, ...args], {
+    env: { ...process.env, ...env },
+    encoding: 'utf8',
+  });
+}
+
+describe('license-keygen: CLI regression', () => {
+  let tmp;
+  beforeEach(() => { tmp = _tmpDir('kg-cli'); });
+  afterEach(() => { _cleanup(tmp); });
+
+  function _setupSecret() {
+    fs.writeFileSync(path.join(tmp, '.license-secret'), TEST_SECRET);
+  }
+
+  test('omitted --start-id uses the auto-counter path (CLI integration)', () => {
+    _setupSecret();
+    const counterFile = path.join(tmp, '.license-counter');
+
+    // First call: no --start-id, expects counter to be created at 1.
+    const out1 = _runCli(['--duration', '30', '--count', '1', '--json'], {
+      LICENSE_COUNTER_FILE: counterFile,
+    });
+    const codes1 = JSON.parse(out1.split('Generated')[0]);
+    expect(codes1).toHaveLength(1);
+    expect(codes1[0].codeId).toBe(1);
+    expect(codes1[0].durationDays).toBe(30);
+    expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe('1');
+
+    // Second call: counter should auto-increment to 2.
+    const out2 = _runCli(['--duration', '30', '--count', '1', '--json'], {
+      LICENSE_COUNTER_FILE: counterFile,
+    });
+    const codes2 = JSON.parse(out2.split('Generated')[0]);
+    expect(codes2[0].codeId).toBe(2);
+    expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe('2');
+  });
+
+  test('--start-id override skips counter file update (CLI integration)', () => {
+    _setupSecret();
+    const counterFile = path.join(tmp, '.license-counter');
+    fs.writeFileSync(counterFile, '99');
+
+    const out = _runCli(['--duration', '30', '--start-id', '500', '--count', '2', '--json'], {
+      LICENSE_COUNTER_FILE: counterFile,
+    });
+    const codes = JSON.parse(out.split('Generated')[0]);
+    expect(codes.map(c => c.codeId)).toEqual([500, 501]);
+    // Counter file untouched.
+    expect(fs.readFileSync(counterFile, 'utf8').trim()).toBe('99');
+  });
+
+  test('--lifetime and --duration are mutually exclusive (CLI integration)', () => {
+    _setupSecret();
+    expect(() =>
+      _runCli(['--duration', '30', '--lifetime', '--count', '1'], {
+        LICENSE_COUNTER_FILE: path.join(tmp, '.license-counter'),
+      }),
+    ).toThrow(/mutually exclusive/);
+  });
+
+  test('--tier pro without --duration or --lifetime still requires one of them', () => {
+    _setupSecret();
+    expect(() =>
+      _runCli(['--tier', 'pro', '--count', '1'], {
+        LICENSE_COUNTER_FILE: path.join(tmp, '.license-counter'),
+      }),
+    ).toThrow(/--duration is required/);
+  });
+});
diff --git a/dashcaddy-api/license-keygen.js b/dashcaddy-api/license-keygen.js
index 24761c9..ee47b77 100644
--- a/dashcaddy-api/license-keygen.js
+++ b/dashcaddy-api/license-keygen.js
@@ -19,9 +19,10 @@ const path = require('path');
 // Master secret file — lives only on admin machine, NEVER shipped
 const SECRET_FILE = path.join(__dirname, '.license-secret');
 
-// License code format: DC-AAAAA-BBBBB-CCCCC-DDDDD
-// Encodes: version(4bit) + duration_days(12bit) + code_id(32bit) + created_ts(32bit) + hmac(48bit)
-// Total: 128 bits = 16 bytes, base32-encoded into 4 groups of 5 chars
+// License code format: DC-AAAAA-BBBBB-CCCCC-DDDDD-EEEEE
+// Encodes: version(4bit) + duration_days(12bit) + code_id(32bit) + created_ts(32bit) + hmac(40bit)
+// Total: 120 bits = 15 bytes, base32-encoded into 5 groups of 5 chars
+// (25 base32 chars = 125 bits, comfortably fits 120 bits of data)
 
 const VALID_DURATIONS = [30, 90, 180, 365];
 const LIFETIME_DURATION = 0; // Admin-only, not publicly available
@@ -61,12 +62,190 @@ function base32Decode(str) {
 
 function getSecret() {
   if (!fs.existsSync(SECRET_FILE)) {
-    console.error('No master secret found. Run with --init-secret first.');
+    console.error('No master secret found at', SECRET_FILE);
+    console.error('Run with --init-secret first.');
     process.exit(1);
   }
   return fs.readFileSync(SECRET_FILE, 'utf8').trim();
 }
 
+// Counter location: the default is `path.join(__dirname, '.license-counter')`.
+// That's adjacent to this source file on the admin machine (not the secret
+// file — the secret and counter share a directory on the developer's
+// workstation, but they are independent files). The CLI does not merge them.
+// When this module is required from a packaged/installed location where
+// __dirname might be read-only, override the counter location via the
+// `LICENSE_COUNTER_FILE` env var. The Stripe bridge uses this same path.
+function _defaultCounterFile() {
+  return process.env.LICENSE_COUNTER_FILE || path.join(__dirname, '.license-counter');
+}
+
+// Atomic counter write — write to a uniquely-named .tmp then rename. The
+// .tmp suffix includes pid + Date.now() + Math.random so two concurrent
+// calls in overlapping event-loop ticks (e.g. a Stripe webhook fan-out)
+// can't collide on the temp name. POSIX rename is atomic on the same
+// filesystem, so the live counter file is never observed in a half-written
+// state. If writeFileSync throws, we re-throw without renaming — the
+// original counter file is intact. If renameSync throws, we attempt to
+// unlink the .tmp so it doesn't accumulate.
+function _atomicWriteCounter(counterFile, value) {
+  const tmpFile = `${counterFile}.tmp.${process.pid}.${Date.now()}.${Math.random().toString(36).slice(2, 8)}`;
+  try {
+    fs.writeFileSync(tmpFile, String(value));
+  } catch (err) {
+    throw new Error(`generateCodes: failed to write counter tmp file ${tmpFile}: ${err.message}`);
+  }
+  try {
+    fs.renameSync(tmpFile, counterFile);
+  } catch (err) {
+    try { fs.unlinkSync(tmpFile); } catch (_) { /* best effort cleanup */ }
+    throw new Error(`generateCodes: failed to rename counter tmp to ${counterFile}: ${err.message}`);
+  }
+}
+
+// Concurrency note: this module is single-threaded JavaScript. Two
+// synchronous calls to generateCodes() within the same event-loop tick
+// cannot interleave — fs.*Sync blocks the thread and the second call runs
+// only after the first returns. The "atomic" part of the counter write
+// protects against a process crash between writeFileSync and renameSync
+// (the original counter file is intact because rename never happened)
+// and against OS-level write atomicity. It does NOT protect against a
+// concurrent process — license-keygen.js is a single-instance admin tool
+// and must not be invoked from multiple processes simultaneously.
+// Callers needing cross-process safety (which is none currently) would
+// need OS-level locking via fcntl or flock — out of scope.
+
+/**
+ * Programmatic equivalent of the CLI's "generate codes" path.
+ *
+ * Differs from the CLI in two ways:
+ *   1. No console output — returns the resulting array.
+ *   2. Persists the counter file atomically (write to a uniquely-named
+ *      .tmp, rename) so a crash mid-write doesn't leave the counter in a
+ *      half-bumped state, and so concurrent calls don't collide on the
+ *      same .tmp name.
+ *
+ * Concurrency: relies on Node's single-threaded event loop. Two
+ * synchronous calls in the same tick cannot interleave — the second call
+ * reads the post-write counter value. The atomic write helper protects
+ * against process crashes between writeFileSync and renameSync, and the
+ * unique .tmp suffix prevents filename collisions across ticks. Cross-process
+ * races are still possible — license-keygen.js is a single-instance admin
+ * tool, so callers must not invoke it from multiple processes simultaneously.
+ *
+ * Returns synchronously. The underlying counter allocator uses fs.*Sync,
+ * so the function never throws asynchronously. Wrap with Promise.resolve()
+ * if your caller needs a Promise.
+ *
+ * @param {Object} opts
+ * @param {string} opts.secret     The master secret (hex string). Callers
+ *                                 are responsible for loading it via
+ *                                 loadSecret() or getSecret().
+ * @param {number} opts.durationDays 30, 90, 180, 365, or 0 for LIFETIME.
+ *                                 Validated against VALID_DURATIONS / LIFETIME.
+ * @param {number} [opts.count=1]  Number of codes to mint.
+ * @param {number} [opts.startId]  Override the auto counter. If omitted,
+ *                                 reads + increments the counter file.
+ * @param {string} [opts.counterFile] Override the counter file path.
+ *                                 Defaults to env LICENSE_COUNTER_FILE or
+ *                                 path.join(__dirname, '.license-counter').
+ * @returns {Array<{code: string, codeId: number, durationDays: number}>}
+ */
+// Throws on bad opts. Returns { secret, durationDays, count } with defaults applied.
+function _validateGenerateOpts(opts) {
+  if (!opts || !opts.secret || typeof opts.secret !== 'string') {
+    throw new Error('generateCodes: secret is required');
+  }
+  const { secret, count = 1 } = opts;
+  const { durationDays } = opts;
+  // LIFETIME (0) is accepted; non-LIFETIME must be in the allowed list.
+  if (durationDays !== 0 && !VALID_DURATIONS.includes(durationDays)) {
+    throw new Error(`generateCodes: invalid duration ${durationDays}. Valid: ${VALID_DURATIONS.join(', ')}`);
+  }
+  if (!Number.isInteger(count) || count < 1 || count > 10000) {
+    throw new Error(`generateCodes: invalid count ${count} (must be 1..10000)`);
+  }
+  return { secret, durationDays, count };
+}
+
+// Resolves the next startId. startIdProvided=true means the caller passed
+// opts.startId (even if the value is invalid — validation happens here).
+// Reads the counter file on the auto path; throws on parse/IO error.
+function _resolveStartId(startIdProvided, overrideStartId, counterFile) {
+  if (startIdProvided) {
+    if (!Number.isInteger(overrideStartId) || overrideStartId < 0 || overrideStartId > 0xFFFFFFFF) {
+      throw new Error(`generateCodes: startId out of range or non-integer (must be 0..0xFFFFFFFF, got ${overrideStartId})`);
+    }
+    return overrideStartId;
+  }
+  try {
+    if (fs.existsSync(counterFile)) {
+      const raw = fs.readFileSync(counterFile, 'utf8').trim();
+      if (!/^\d+$/.test(raw)) {
+        throw new Error(`counter file ${counterFile} contains non-numeric value '${raw}'`);
+      }
+      return parseInt(raw, 10) + 1;
+    }
+    return 1;
+  } catch (err) {
+    if (err.message && err.message.startsWith('counter file ')) throw err;
+    throw new Error(`generateCodes: failed to read counter file ${counterFile}: ${err.message}`);
+  }
+}
+
+function generateCodes(opts) {
+  const { secret, durationDays, count } = _validateGenerateOpts(opts);
+  const overrideCounterFile = opts && opts.counterFile;
+  const counterFile = overrideCounterFile || _defaultCounterFile();
+
+  // Validate startId BEFORE selecting the allocation path. Any explicitly
+  // supplied startId (including floats, NaN, null, numeric strings) must
+  // either be a valid integer in range or throw — we use
+  // Object.prototype.hasOwnProperty to distinguish "caller passed startId"
+  // from "caller omitted startId" so the overrideStartId validation runs
+  // regardless of value.
+  const startIdProvided = opts && Object.prototype.hasOwnProperty.call(opts, 'startId');
+  const overrideStartId = startIdProvided ? opts.startId : undefined;
+  const startId = _resolveStartId(startIdProvided, overrideStartId, counterFile);
+
+  // Validate that the requested range fits in the code_id field (32 bits).
+  const lastCodeId = startId + count - 1;
+  if (lastCodeId > 0xFFFFFFFF) {
+    throw new Error(`generateCodes: codeId range exceeds 32-bit limit (startId=${startId}, count=${count}, lastCodeId=${lastCodeId})`);
+  }
+
+  const codes = [];
+  for (let i = 0; i < count; i++) {
+    const codeId = startId + i;
+    const code = generateCode(secret, durationDays, codeId);
+    codes.push({ code, codeId, durationDays });
+  }
+
+  // Persist the new counter value (skipped when startId was overridden).
+  if (!startIdProvided) {
+    _atomicWriteCounter(counterFile, lastCodeId);
+  }
+
+  return codes;
+}
+
+/**
+ * Load the master secret from disk. Exported so the Stripe bridge can
+ * call it without going through getSecret() (which prints to stderr and
+ * exits on missing-secret — wrong semantics for a library call).
+ *
+ * @param {string} [overridePath] Defaults to the SECRET_FILE constant.
+ * @returns {string} The hex secret.
+ * @throws If the file is missing or unreadable.
+ */
+function loadSecret(overridePath) {
+  const file = overridePath || SECRET_FILE;
+  if (!fs.existsSync(file)) {
+    throw new Error(`Master secret file not found at ${file}. Run --init-secret first.`);
+  }
+  return fs.readFileSync(file, 'utf8').trim();
+}
+
 function initSecret() {
   if (fs.existsSync(SECRET_FILE)) {
     console.error('Master secret already exists at', SECRET_FILE);
@@ -193,19 +372,23 @@ function main() {
 DashCaddy License Code Generator
 
 Usage:
-  node license-keygen.js --init-secret              Initialize master secret (first time only)
-  node license-keygen.js --duration <days> [options] Generate license codes
-  node license-keygen.js --verify <code>             Verify a license code
-  node license-keygen.js --decode <code>             Decode and display code details
+  node license-keygen.js --init-secret                        Initialize master secret (first time only)
+  node license-keygen.js --duration <days> [options]          Generate Pro license codes
+  node license-keygen.js --lifetime [options]                 Generate a LIFETIME code (creator-only)
+  node license-keygen.js --verify <code>                       Verify a license code
+  node license-keygen.js --decode <code>                       Decode and display code details
 
 Options:
-  --duration <days>    Code validity: 30, 90, 180, or 365 days (required for generation)
+  --duration <days>    Code validity: 30, 90, 180, or 365 days (required for generation, mutually exclusive with --lifetime)
+  --tier <tier>        Tier label; only 'pro' is supported (optional label; valid in combination with --duration or --lifetime)
+  --lifetime           Generate a LIFETIME code — REJECTED at activation on production hosts
   --count <n>          Number of codes to generate (default: 1)
   --start-id <n>       Starting code ID (default: auto from counter file)
   --output <file>      Write codes to file instead of stdout
   --json               Output as JSON
 
 Valid durations: ${VALID_DURATIONS.join(', ')} days
+Valid tiers: pro (cosmetic alias; does not change generation behavior)
     `);
     process.exit(0);
   }
@@ -244,9 +427,31 @@ Valid durations: ${VALID_DURATIONS.join(', ')} days
 
   // Generate codes
   const isLifetime = args.includes('--lifetime');
+
+  // --tier is a cosmetic label right now (only 'pro' is supported). It does
+  // NOT change generation behavior — every code minted with --duration is
+  // already a Pro code, and --lifetime is enforced separately at activation
+  // time. The flag exists to make operator intent obvious in shell history
+  // and to reserve a forward-compatible hook for a future tier that needs
+  // to alter code generation (e.g. a 'free' tier with a different prefix).
+  // It is only meaningful in combination with --duration or --lifetime —
+  // by itself, generation still requires one of those flags.
+  const tierIndex = args.indexOf('--tier');
+  if (tierIndex !== -1) {
+    const tier = (args[tierIndex + 1] || '').toLowerCase();
+    if (tier !== 'pro') {
+      console.error(`Invalid tier: '${tier}'. Supported: pro.`);
+      process.exit(1);
+    }
+  }
+
   const durationIndex = args.indexOf('--duration');
   if (!isLifetime && durationIndex === -1) {
-    console.error('--duration is required. Use --help for usage.');
+    console.error('--duration is required (or use --lifetime). Use --help for usage.');
+    process.exit(1);
+  }
+  if (isLifetime && durationIndex !== -1) {
+    console.error('--lifetime and --duration are mutually exclusive.');
     process.exit(1);
   }
   const duration = isLifetime ? LIFETIME_DURATION : parseInt(args[durationIndex + 1]);
@@ -258,29 +463,20 @@ Valid durations: ${VALID_DURATIONS.join(', ')} days
   const countIndex = args.indexOf('--count');
   const count = countIndex !== -1 ? parseInt(args[countIndex + 1]) : 1;
 
-  // Load or create counter file for auto-incrementing code IDs
-  const counterFile = path.join(__dirname, '.license-counter');
-  let startId;
   const startIdIndex = args.indexOf('--start-id');
-  if (startIdIndex !== -1) {
-    startId = parseInt(args[startIdIndex + 1]);
-  } else if (fs.existsSync(counterFile)) {
-    startId = parseInt(fs.readFileSync(counterFile, 'utf8').trim()) + 1;
-  } else {
-    startId = 1;
-  }
+  const overrideStartId = startIdIndex !== -1 ? parseInt(args[startIdIndex + 1]) : undefined;
 
   const secret = getSecret();
-  const codes = [];
-
-  for (let i = 0; i < count; i++) {
-    const codeId = startId + i;
-    const code = generateCode(secret, duration, codeId);
-    codes.push({ code, codeId, durationDays: duration });
+  // Only pass startId when --start-id was supplied on the CLI. generateCodes
+  // uses Object.prototype.hasOwnProperty.call(opts, 'startId') to distinguish
+  // "caller passed startId" from "caller omitted startId" and rejects
+  // non-integer values. Passing startId: undefined would mean "caller passed
+  // undefined", which the validation path then rejects.
+  const generateOpts = { secret, durationDays: duration, count };
+  if (overrideStartId !== undefined) {
+    generateOpts.startId = overrideStartId;
   }
-
-  // Save counter
-  fs.writeFileSync(counterFile, String(startId + count - 1));
+  const codes = generateCodes(generateOpts);
 
   // Output
   const outputIndex = args.indexOf('--output');
@@ -302,11 +498,26 @@ Valid durations: ${VALID_DURATIONS.join(', ')} days
     }
   }
 
-  console.log(`\nGenerated ${count} code(s) for ${duration === 0 ? 'LIFETIME' : duration + ' days'}. Next ID: ${startId + count}`);
+  const lastCodeId = codes[codes.length - 1].codeId;
+  console.log(`\nGenerated ${count} code(s) for ${duration === 0 ? 'LIFETIME' : duration + ' days'}. Next ID: ${lastCodeId + 1}`);
 }
 
-// Also export for use by license-manager.js
-module.exports = { verifyCode, parseCode, VALID_DURATIONS, VERSION };
+// Also export for use by license-manager.js and the Stripe webhook bridge.
+// `generateCode` is exported so the bridge can mint codes in-process rather
+// than spawning a child process (faster, atomic counter, easier to test).
+// `generateCodes` (note the trailing 's') is the bulk-friendly wrapper that
+// handles the counter-file write and returns a stable array of {code, codeId,
+// durationDays} records — used by the bridge when one Stripe event must
+// produce one code (typical case is just 1, but the API is uniform).
+module.exports = {
+  verifyCode,
+  parseCode,
+  generateCode,
+  generateCodes,
+  loadSecret,
+  VALID_DURATIONS,
+  VERSION,
+};
 
 if (require.main === module) {
   main();