diff --git a/docs/runbooks/first-user-walk.md b/docs/runbooks/first-user-walk.md
index 2724dd569..68ff71d21 100644
--- a/docs/runbooks/first-user-walk.md
+++ b/docs/runbooks/first-user-walk.md
@@ -18,11 +18,33 @@ rename it without changing the exclusion list too.
 
 ## Run it
 
+### Prod: sign in to the existing test account
+
+Prod has no signup for the walk. The run signs in to one existing test account
+and runs the six covered steps (login, first pod, hosted install, hosted reply,
+invite preview, and the BYO step that reports not-covered). It removes only the
+pod, seat and agent it made, and it never deletes the account.
+
 ```bash
-COMMONLY_WALK_PASSWORD="$(openssl rand -base64 24)" \
+COMMONLY_WALK_EMAIL=<existing test account> \
+COMMONLY_WALK_PASSWORD="<its password>" \
   node scripts/first-user-walk.mjs --base https://api.commonly.me
 ```
 
+- Without `COMMONLY_WALK_EMAIL` a prod run is refused before any request.
+- The manifest records `"mode": "signin-prod"`. The result file has no
+  `signup` or `signup-workspace` steps.
+
+### Signup (non-prod targets with no account given)
+
+Prod never signs up. A prod base without `COMMONLY_WALK_EMAIL` is refused before
+any request, so this form is for other targets only:
+
+```bash
+COMMONLY_WALK_PASSWORD="$(openssl rand -base64 24)" \
+  node scripts/first-user-walk.mjs --base https://api-dev.example.test
+```
+
 - Generate a fresh password per run. The script reads it from the environment
   and never writes it anywhere. Do not put a credential in the command you
   paste into a pod, a PR or a task row.
@@ -45,8 +67,10 @@ COMMONLY_WALK_EMAIL=<shared walk account> COMMONLY_WALK_PASSWORD=<its password>
 - The run signs in and never signs up. It removes only the pods, seats and
   agents it created, and it never deletes the shared account.
 - `COMMONLY_WALK_EMAIL` aimed at any host other than staging is refused before
-  the walk starts, so the shared account cannot be used on prod.
-- The manifest records `"mode": "signin"` for these runs.
+  the walk starts. Prod uses the same variable name, so keep staging credentials
+  out of a shell that runs the walk against prod.
+- The manifest records `"mode": "signin"` for these runs. Prod runs record
+  `"mode": "signin-prod"`.
 
 ## Cleanup is part of the run
 
@@ -88,7 +112,7 @@ Write is atomic (temp file, then rename), so a reader never sees a half file.
   "schema": 1,
   "sha": "<deployed sha from WALK_SHA, or null when the scheduler did not set it>",
   "startedAt": "...", "finishedAt": "...",
-  "base": "https://api.commonly.me", "mode": "signup",
+  "base": "https://api.commonly.me", "mode": "signin-prod",
   "walk": "walk-<stamp>",
   "overall": "pass | fail | incomplete",
   "exitCode": 0,
@@ -103,7 +127,7 @@ Write is atomic (temp file, then rename), so a reader never sees a half file.
   (Bring your own connect). Today every full run is `incomplete`, never `pass`,
   until that step is built. Roll back on `fail` only; treat `incomplete` as
   not-green but not as a regression.
-- `mode` is `signup` or `signin`, or `not-chosen` when the run was refused before a mode was accepted (no request was made).
+- `mode` is `signup`, `signin` (staging) or `signin-prod`, or `not-chosen` when the run was refused before a mode was accepted (no request was made).
 - `cleanup.status` is `not-run` (and `ok` null) when the run stopped before cleanup could start, for example a refused mode.
 - The file holds no password, token or email. A `needs-admin-purge` cleanup
   points SRE at the manifest in `~/.commonly/state/walk-706/`.
diff --git a/scripts/first-user-walk-mode.mjs b/scripts/first-user-walk-mode.mjs
index 17baa8301..f8ead15a4 100644
--- a/scripts/first-user-walk-mode.mjs
+++ b/scripts/first-user-walk-mode.mjs
@@ -1,18 +1,28 @@
-// How the walk gets its account (TASK-706). Prod signs up a fresh account every
-// run. Staging needs a verified email, which a walk address cannot receive, so
-// SRE pre-verifies one shared walk account there and the walk signs in to it
-// instead. Its credentials come from env only, and that account is never deleted.
-// Exact host and https only: a substring match would send the shared password to
-// any host whose name contains "staging".
+// How the walk gets its account (TASK-706, TASK-729). Staging needs a verified
+// email, which a walk address cannot receive, so SRE pre-verifies one shared walk
+// account there and the walk signs in to it instead. Prod has no signup for the
+// walk: it signs in to an existing test account, and that account is never
+// deleted. Signup runs only on non-prod targets with no account given.
+// Credentials come from env only. Exact host and https only: a substring match
+// would send a shared password to any host whose name contains "staging".
 const STAGING_HOSTS = new Set(['api-staging.commonly.me']);
+const PROD_HOSTS = new Set(['api.commonly.me']);
 
 // `deleteAccount` is the one value main() hands to cleanup, so the mode decides
-// the account's fate here and nowhere else.
+// the account's fate here and nowhere else. The password is always COMMONLY_WALK_PASSWORD.
 export const chooseWalkMode = ({ base, env }) => {
+  const url = new URL(base);
+  // A trailing dot names the same host but would slip past the exact-host checks below.
+  const host = url.hostname.replace(/\.$/, '');
   const email = env.COMMONLY_WALK_EMAIL || '';
+  // Checked before the prod branch: over plain http the signup path would send the password in cleartext.
+  if (PROD_HOSTS.has(host) && url.protocol !== 'https:') throw new Error('prod walk requires https; refusing before any request');
+  if (url.protocol === 'https:' && PROD_HOSTS.has(host)) {
+    if (!email) throw new Error('prod has no walk signup: set COMMONLY_WALK_EMAIL to an existing test account');
+    return { mode: 'signin-prod', email, deleteAccount: false };
+  }
   if (!email) return { mode: 'signup', deleteAccount: true };
-  const url = new URL(base);
-  if (url.protocol !== 'https:' || !STAGING_HOSTS.has(url.hostname)) {
+  if (url.protocol !== 'https:' || !STAGING_HOSTS.has(host)) {
     throw new Error('COMMONLY_WALK_EMAIL is set but the target is not the staging API over https; the shared sign-in account exists on staging only');
   }
   return { mode: 'signin', email, deleteAccount: false };
diff --git a/scripts/first-user-walk-mode.test.mjs b/scripts/first-user-walk-mode.test.mjs
index 363fa3041..a2870573e 100644
--- a/scripts/first-user-walk-mode.test.mjs
+++ b/scripts/first-user-walk-mode.test.mjs
@@ -10,15 +10,19 @@ test('staging with COMMONLY_WALK_EMAIL takes the sign-in path', () => {
   assert.deepEqual(chooseWalkMode({ base: STAGING, env: { COMMONLY_WALK_EMAIL: 'walk@commonly.me' } }), { mode: 'signin', email: 'walk@commonly.me', deleteAccount: false });
 });
 
-test('no COMMONLY_WALK_EMAIL signs up a fresh account, on any target, and that account is deleted', () => {
-  assert.deepEqual(chooseWalkMode({ base: PROD, env: {} }), { mode: 'signup', deleteAccount: true });
+test('no COMMONLY_WALK_EMAIL signs up a fresh account on staging, and that account is deleted', () => {
   assert.deepEqual(chooseWalkMode({ base: STAGING, env: {} }), { mode: 'signup', deleteAccount: true });
 });
 
-test('the shared sign-in account is refused on prod', () => {
-  assert.throws(() => chooseWalkMode({ base: PROD, env: { COMMONLY_WALK_EMAIL: 'walk@commonly.me' } }), /staging only/);
+test('prod never signs up: it signs in to the existing account from env, which is never deleted', () => {
+  assert.deepEqual(chooseWalkMode({ base: PROD, env: { COMMONLY_WALK_EMAIL: 'walk-test@commonly.me' } }), { mode: 'signin-prod', email: 'walk-test@commonly.me', deleteAccount: false });
 });
 
+test('prod without an existing test account is refused, not signed up', () => {
+  assert.throws(() => chooseWalkMode({ base: PROD, env: {} }), /no walk signup/);
+});
+
+
 test('a host that merely contains "staging" never receives the shared account', () => {
   for (const base of ['https://staging.attacker.example', 'https://api-staging.commonly.me.attacker.example', 'https://evil-staging.example']) {
     assert.throws(() => chooseWalkMode({ base, env: { COMMONLY_WALK_EMAIL: 'walk@commonly.me' } }), /staging API over https/, base);
diff --git a/scripts/first-user-walk.mjs b/scripts/first-user-walk.mjs
index c9a1b8f25..14e43a08e 100644
--- a/scripts/first-user-walk.mjs
+++ b/scripts/first-user-walk.mjs
@@ -20,7 +20,13 @@
  * token or the email.
  *
  * Usage:
- *   COMMONLY_WALK_PASSWORD=... node scripts/first-user-walk.mjs [--base https://api.commonly.me]
+ *   COMMONLY_WALK_EMAIL=... COMMONLY_WALK_PASSWORD=... \
+ *     node scripts/first-user-walk.mjs [--base https://api.commonly.me]
+ *
+ * Prod: no signup. The run signs in to one existing test account (the email and
+ * password above, from env only), runs the six covered steps, removes only what it
+ * created, and never deletes that account. Without COMMONLY_WALK_EMAIL a prod run
+ * is refused before any request.
  *
  * Staging: signup needs a verified email, so SRE's shared walk account is used
  * instead. Set COMMONLY_WALK_EMAIL and COMMONLY_WALK_PASSWORD from env (never a
@@ -241,9 +247,9 @@ export const runWalk = async ({
   // Starts false: a cleanup that throws must not be reported as ok.
   let cleanupOk = false;
   try {
-    expect(password, 'COMMONLY_WALK_PASSWORD is not set');
     walkMode = chooseWalkMode({ base: BASE, env });
-    if (walkMode.mode === 'signin') email = walkMode.email;
+    expect(password, 'COMMONLY_WALK_PASSWORD is not set');
+    if (walkMode.email) email = walkMode.email;
     manifest.mode = walkMode.mode;
 
     let token = null;
diff --git a/scripts/first-user-walk.test.mjs b/scripts/first-user-walk.test.mjs
index eebdc48f4..931835ff2 100644
--- a/scripts/first-user-walk.test.mjs
+++ b/scripts/first-user-walk.test.mjs
@@ -23,7 +23,7 @@ const SHARED_EMAIL = 'walk-shared@commonly.test';
 const fakeBackend = ({
   preview = 200, create = 'ok', password = PASSWORD, echoRegister = false, seeded = false,
 } = {}) => {
-  const state = { accountExists: seeded, pods: [], lastAgent: null, calls: [] };
+  const state = { accountExists: seeded, pods: [], lastAgent: null, calls: [], loginEmails: [] };
   const reply = (status, data) => ({ status, json: async () => data });
   const fetchImpl = async (url, init = {}) => {
     const u = new URL(url);
@@ -40,6 +40,7 @@ const fakeBackend = ({
       return reply(201, {});
     }
     if (method === 'POST' && p === '/api/auth/login') {
+      state.loginEmails.push(body.email);
       if (state.accountExists && body.password === password) {
         return reply(200, { token: TOKEN, user: { _id: USER_ID, role: 'user' } });
       }
@@ -95,7 +96,8 @@ const dirs = () => {
   return { stateDir: path.join(root, 'state'), resultPath: path.join(root, 'result', 'result.json') };
 };
 
-const run = (fetchImpl, { stateDir, resultPath }, { password = PASSWORD, env = {}, base = 'https://api.commonly.me' } = {}) => runWalk({
+// Non-prod, non-staging by default: a run with no account given signs up, as the signup tests expect.
+const run = (fetchImpl, { stateDir, resultPath }, { password = PASSWORD, env = {}, base = 'https://api-dev.commonly.test' } = {}) => runWalk({
   base,
   env: { COMMONLY_WALK_PASSWORD: password, ...env },
   fetchImpl,
@@ -198,6 +200,50 @@ test('signin mode never deletes the shared account, and the result says so', asy
   assert.equal(result.steps.some((s) => s.name === 'signup-workspace'), false);
 });
 
+test('prod signs in to the existing test account: no signup, the six covered steps, the account is never deleted', async () => {
+  const dirsFor = dirs();
+  const { fetchImpl, state } = fakeBackend({ seeded: true });
+  const { exitCode, result } = await run(fetchImpl, dirsFor, {
+    base: 'https://api.commonly.me',
+    env: { COMMONLY_WALK_EMAIL: 'walk-test@commonly.test' },
+  });
+
+  assert.equal(result.mode, 'signin-prod');
+  assert.equal(exitCode, 2);
+  assert.equal(result.overall, 'incomplete');
+  assert.deepEqual(result.steps.map((st) => st.name), ['login', 'first-pod', 'hosted-install', 'hosted-reply', 'invite-preview-api', 'byo-connect']);
+  assert.equal(state.calls.includes('POST /api/auth/register'), false);
+  assert.equal(state.calls.includes('DELETE /api/users/me'), false);
+  assert.equal(state.accountExists, true);
+  assert.equal(state.pods.length, 0);
+  assert.equal(result.cleanup.ok, true);
+  // The run signs in with the env email, and that email never reaches the result or manifest.
+  assert.deepEqual(state.loginEmails, ['walk-test@commonly.test']);
+  assert.equal(readFileSync(dirsFor.resultPath, 'utf8').includes('walk-test@commonly.test'), false);
+  const [manifestFile] = readdirSync(dirsFor.stateDir);
+  assert.equal(readFileSync(path.join(dirsFor.stateDir, manifestFile), 'utf8').includes('walk-test@commonly.test'), false);
+});
+
+test('a trailing dot on the prod host is still prod: refused without an account, never signed up', async () => {
+  const dirsFor = dirs();
+  const { fetchImpl, state } = fakeBackend();
+  const { exitCode } = await run(fetchImpl, dirsFor, { base: 'https://api.commonly.me.' });
+
+  assert.equal(exitCode, 1);
+  assert.equal(state.calls.includes('POST /api/auth/register'), false);
+  assert.equal(state.calls.length, 0);
+});
+
+test('prod without an existing test account is refused before any request', async () => {
+  const dirsFor = dirs();
+  const { fetchImpl, state } = fakeBackend({ seeded: true });
+  const { exitCode, result } = await run(fetchImpl, dirsFor, { base: 'https://api.commonly.me' });
+
+  assert.equal(exitCode, 1);
+  assert.equal(result.mode, 'not-chosen');
+  assert.equal(state.calls.length, 0);
+});
+
 test('a refused mode (shared email aimed at prod) makes no request, is not reported as signup, and exits 1', async () => {
   const dirsFor = dirs();
   const { fetchImpl, state } = fakeBackend({ seeded: true });
@@ -246,7 +292,7 @@ test('a missing password fails before any request, reports cleanup as not-run, a
   const counting = (url, init) => { requests += 1; return fetchImpl(url, init); };
   const { exitCode, result } = await runWalk({
     base: 'https://api.commonly.me',
-    env: {},
+    env: { COMMONLY_WALK_EMAIL: 'walk-test@commonly.test' },
     fetchImpl: counting,
     ...dirsFor,
     sleep: async () => {},
@@ -255,11 +301,22 @@ test('a missing password fails before any request, reports cleanup as not-run, a
   });
   assert.equal(exitCode, 1);
   assert.equal(result.overall, 'fail');
+  assert.equal(result.mode, 'signin-prod');
   assert.equal(result.cleanup.status, 'not-run');
   assert.equal(requests, 0);
   assert.equal(existsSync(dirsFor.resultPath), true);
 });
 
+test('prod over plain http is refused before any request, so the password never goes out in cleartext', async () => {
+  const dirsFor = dirs();
+  const { fetchImpl, state } = fakeBackend();
+  const { exitCode, result } = await run(fetchImpl, dirsFor, { base: 'http://api.commonly.me' });
+
+  assert.equal(exitCode, 1);
+  assert.equal(result.mode, 'not-chosen');
+  assert.equal(state.calls.length, 0);
+});
+
 test('a create that throws, with no match in the list, is recorded as unresolved and needs-admin-purge', async () => {
   const dirsFor = dirs();
   const { fetchImpl, state } = fakeBackend({ create: 'throw' });