diff --git a/.env.example b/.env.example
index 9cfa0a2e..c3f62d94 100644
--- a/.env.example
+++ b/.env.example
@@ -208,6 +208,20 @@ DB_PASSWORD=pedscribe_secret_change_me
 # ── Mail ────────────────────────────────────────────────────────────────────
 # SMTP_SECURE=false               # true for implicit TLS (port 465)
 
+# ── Admin lockdown ──────────────────────────────────────────────────────────
+# With several admins, everything in the admin panel is editable by all of
+# them. Set this and configuration becomes read-only in the panel and refused
+# by the server: prompts, model policy, retrieval limits and budgets, TTS/STT,
+# embeddings, SMTP and email templates. Day-to-day operation stays available —
+# announcements, registration and invitations, feature flags, site details.
+# A setting added later is locked until it is deliberately added to the
+# editable list, rather than defaulting to open.
+#
+# It is deliberately an environment variable: a setting could be switched off
+# by the very admin it restrains, so lifting it needs host access and a
+# restart. Read access is unaffected — locked settings stay visible.
+# ADMIN_LOCKDOWN=false
+
 # ── Identity and limits ─────────────────────────────────────────────────────
 # SITE_NAME=Pediatric AI Scribe
 # API_RATE_LIMIT_MAX=200          # requests per window across /api
diff --git a/public/js/admin.js b/public/js/admin.js
index 4644d426..7ed48c36 100644
--- a/public/js/admin.js
+++ b/public/js/admin.js
@@ -1462,6 +1462,50 @@ initImageSettings();
 
 }
 
+// ============================================================
+// ADMIN LOCKDOWN (display)
+// The server refuses locked writes regardless; this only stops an admin
+// filling in a field that was never going to save. Settings stay visible, so
+// the configuration can still be read.
+//
+// The state rides along on the invites response rather than a request of its
+// own: the admin panel already makes enough calls on open.
+// ============================================================
+{
+  window.applyAdminLockdown = function(state) {
+    if (!state || !state.enabled) return;
+    var panel = document.getElementById('admin-tab');
+    if (!panel || !panel.querySelector('.card')) return;
+    lockdownBanner(panel, state);
+    lockdownFields(panel, state);
+  };
+
+  function lockdownBanner(panel, state) {
+    if (document.getElementById('admin-lockdown-banner')) return;
+    var note = document.createElement('div');
+    note.id = 'admin-lockdown-banner';
+    note.style.cssText = 'margin:0 0 12px;padding:10px 14px;border:1px solid var(--amber);background:var(--amber-light);border-radius:8px;font-size:13px;color:var(--g800);';
+    note.innerHTML = '<i class="fas fa-lock"></i> <strong>Admin lockdown is on.</strong> ' +
+      adminEscapeHtml(state.reason) + ' Settings are shown but cannot be changed here.';
+    panel.insertBefore(note, panel.firstChild);
+  }
+
+  // Everything inside the panel, except the controls that stay operational and
+  // the buttons that only read.
+  function lockdownFields(panel, state) {
+    var editable = ['admin-invite', 'btn-create-invite', 'cms-ann', 'announcement',
+      'admin-users-search', 'registration'];
+    panel.querySelectorAll('input, select, textarea, button').forEach(function(el) {
+      var id = el.id || '';
+      if (editable.some(function(prefix) { return id.indexOf(prefix) === 0; })) return;
+      var label = (el.textContent || '') + ' ' + id;
+      if (/search|test|discover|refresh|reload|retry|copy/i.test(label)) return;
+      el.disabled = true;
+      el.title = state.reason;
+    });
+  }
+}
+
 // ============================================================
 // ADMIN REGISTRATION INVITES
 // The code exists in readable form exactly once: in the response to creating
@@ -1500,6 +1544,8 @@ initImageSettings();
         var toggle = document.getElementById('admin-invite-only');
         if (toggle) toggle.checked = !!data.inviteOnly;
         renderInvites(data.invites || []);
+        // Painted after the panel has rendered, from the same response.
+        if (typeof window.applyAdminLockdown === 'function') window.applyAdminLockdown(data.lockdown);
       })
       .catch(function() {});
   }
diff --git a/src/routes/adminConfig.js b/src/routes/adminConfig.js
index 30099f4e..0cfea4bd 100644
--- a/src/routes/adminConfig.js
+++ b/src/routes/adminConfig.js
@@ -19,6 +19,26 @@ var { getLiteLLMEmbeddingModels } = require('../utils/embeddings');
 
 router.use(authMiddleware);
 
+var lockdown = require('../utils/adminLockdown');
+
+// One gate rather than a check in every write route, because that list grows
+// and a new route added later would quietly miss it. Reads always pass —
+// lockdown hides nothing, it only refuses changes.
+//
+// Under lockdown a write is refused unless it is day-to-day operation:
+//   - invitations, which is running the service, not configuring it;
+//   - the "test" endpoints, which send a probe and persist nothing;
+//   - /config/:key, which decides per key — some keys stay editable, and that
+//     route applies lockdown.isLocked() itself.
+// Everything else — model policy, SMTP, prompts, resets — is configuration.
+var OPERATIONAL_WRITE = /^\/invites(\/|$)|\/test(-email)?$|^\/config\/[^/]+$/;
+
+router.use(function(req, res, next) {
+  if (!lockdown.enabled() || req.method === 'GET' || req.method === 'HEAD') return next();
+  if (OPERATIONAL_WRITE.test(req.path)) return next();
+  return res.status(403).json({ error: lockdown.refusal(req.path.replace(/^\/config\//, '')) });
+});
+
 function liteLLMBaseUrl() {
   return (process.env.LITELLM_API_BASE || '').replace(/\/+$/, '').replace(/\/v1\/?$/, '');
 }
@@ -91,7 +111,7 @@ router.get('/config', async function(req, res) {
         rows.push({ key: dbKey, value: PROMPTS[key], updated_at: null });
       }
     });
-    res.json({ success: true, config: rows, conversationBudget: budget });
+    res.json({ success: true, config: rows, conversationBudget: budget, lockdown: lockdown.state() });
   } catch (e) { res.status(e.statusCode || 500).json({ error: 'Request failed' }); }
 });
 
@@ -680,7 +700,7 @@ var invites = require('../utils/registrationInvites');
 
 router.get('/invites', async function(req, res) {
   try {
-    res.json({ success: true, invites: await invites.list(), inviteOnly: await invites.inviteOnly() });
+    res.json({ success: true, invites: await invites.list(), inviteOnly: await invites.inviteOnly(), lockdown: lockdown.state() });
   } catch (e) { return serverError(res, 'Invites list', e, 'Could not list invitations'); }
 });
 
@@ -884,6 +904,12 @@ router.put('/config/:key(*)', async function(req, res) {
       return res.status(400).json({ error: 'Unknown config key' });
     }
 
+    // Some settings stay editable under lockdown; the rest are refused here,
+    // whatever the UI showed.
+    if (lockdown.isLocked(key)) {
+      return res.status(403).json({ error: lockdown.refusal(key) });
+    }
+
     // Model policy mutations must use the validated model endpoints.
     if (key.startsWith('models.')) return res.status(400).json({ error: 'Use the model configuration endpoints' });
     if (key.startsWith('feature.') && !['true', 'false'].includes(String(value))) return res.status(400).json({ error: 'Feature value must be true or false' });
diff --git a/src/utils/adminLockdown.js b/src/utils/adminLockdown.js
new file mode 100644
index 00000000..329773b8
--- /dev/null
+++ b/src/utils/adminLockdown.js
@@ -0,0 +1,79 @@
+// ============================================================
+// ADMIN LOCKDOWN
+// With several admins, everything in the admin panel is editable by all of
+// them — prompts, model policy, retrieval limits, SMTP. Lockdown separates
+// "runs the service day to day" from "changes how the service behaves".
+//
+// It is an environment variable, deliberately, not a setting. A setting could
+// be switched off by any admin, which would make it decoration. Only someone
+// with access to the host and a restart can lift it.
+//
+// Locked settings stay visible — an admin should be able to see how the system
+// is configured — but the field is read-only and the server refuses the write.
+// The refusal is the real control; the read-only field is only courtesy.
+// ============================================================
+
+// Everything that changes how the assistant answers, what it costs, or how mail
+// leaves the building.
+var LOCKED_PREFIXES = Object.freeze([
+  'prompt.',              // every prompt, including the clinical ones
+  'clinical_assistant.',  // models, allowlists, retrieval limits, budgets
+  'models.',              // model policy: default, custom, enabled set
+  'tts.',
+  'stt.',
+  'embeddings.',
+  'smtp.',                // where mail goes and who it authenticates as
+  'email.'                // the templates that mail sends
+]);
+
+// Day-to-day operation stays with ordinary admins.
+var EDITABLE_WHEN_LOCKED = Object.freeze([
+  'announcement.',
+  'registration_enabled',
+  'registration_invite_only',
+  'feature.',
+  'site.'
+]);
+
+function enabled(env) {
+  var raw = (env || process.env).ADMIN_LOCKDOWN;
+  return String(raw == null ? '' : raw).toLowerCase() === 'true';
+}
+
+// A key is locked when lockdown is on and it is not on the day-to-day list.
+// Anything unrecognised is locked: a setting added later should need a
+// deliberate decision to become editable, rather than defaulting to open.
+function isLocked(key, env) {
+  if (!enabled(env)) return false;
+  var name = String(key || '');
+  for (var i = 0; i < EDITABLE_WHEN_LOCKED.length; i++) {
+    var allowed = EDITABLE_WHEN_LOCKED[i];
+    if (name === allowed || (allowed.endsWith('.') && name.startsWith(allowed))) return false;
+  }
+  return true;
+}
+
+// What the admin UI needs to render itself correctly.
+function state(env) {
+  return {
+    enabled: enabled(env),
+    lockedPrefixes: LOCKED_PREFIXES.slice(),
+    editablePrefixes: EDITABLE_WHEN_LOCKED.slice(),
+    reason: 'ADMIN_LOCKDOWN is set on the server. Locked settings can only be changed by someone with host access.'
+  };
+}
+
+// One message, so every refusal reads the same wherever it comes from.
+function refusal(key) {
+  return 'This setting is locked. The server is in admin lockdown (ADMIN_LOCKDOWN), ' +
+    'so "' + key + '" can only be changed by someone with host access.';
+}
+
+module.exports = {
+  LOCKED_PREFIXES,
+  EDITABLE_WHEN_LOCKED,
+  enabled,
+  isLocked,
+  state,
+  refusal
+};
diff --git a/test/backend-hardening.test.js b/test/backend-hardening.test.js
index 26067df2..d272ec8b 100644
--- a/test/backend-hardening.test.js
+++ b/test/backend-hardening.test.js
@@ -192,3 +192,50 @@ test('registration invites are single-use, expiring, and safe to store', () => {
   // And the rejection must not say which of the four reasons applied.
   assert.match(auth, /may have expired, been revoked, or already been used/);
 });
+
+// With several admins, everything in the panel was editable by all of them.
+// Lockdown separates running the service from changing how it behaves.
+test('admin lockdown refuses configuration writes at the server', () => {
+  const lockdown = require('../src/utils/adminLockdown');
+  const off = {};
+  const on = { ADMIN_LOCKDOWN: 'true' };
+
+  // It is an environment variable, not a setting: a setting could be switched
+  // off by the very admin it restrains.
+  assert.equal(lockdown.enabled(off), false);
+  assert.equal(lockdown.enabled({ ADMIN_LOCKDOWN: 'false' }), false);
+  assert.equal(lockdown.enabled(on), true);
+
+  // Off, nothing is locked.
+  assert.equal(lockdown.isLocked('prompt.hpi', off), false);
+
+  // On, configuration is locked and day-to-day operation is not.
+  for (const key of ['prompt.hpi', 'clinical_assistant.chat_model', 'models.default',
+    'tts.voice', 'stt.model', 'embeddings.model', 'smtp.host', 'email.verify.subject']) {
+    assert.equal(lockdown.isLocked(key, on), true, key + ' is locked');
+  }
+  for (const key of ['announcement.text', 'registration_enabled',
+    'registration_invite_only', 'feature.memories', 'site.name']) {
+    assert.equal(lockdown.isLocked(key, on), false, key + ' stays editable');
+  }
+
+  // A setting added later is locked until someone decides otherwise, rather
+  // than defaulting to open.
+  assert.equal(lockdown.isLocked('something.invented.later', on), true);
+
+  const fs = require('node:fs');
+  const path = require('node:path');
+  const admin = fs.readFileSync(path.join(__dirname, '..', 'src/routes/adminConfig.js'), 'utf8');
+  // One gate, not a check per route: a route added later cannot miss it.
+  assert.match(admin, /if \(!lockdown\.enabled\(\) \|\| req\.method === 'GET' \|\| req\.method === 'HEAD'\) return next\(\);/);
+  assert.match(admin, /if \(OPERATIONAL_WRITE\.test\(req\.path\)\) return next\(\);/);
+  assert.match(admin, /return res\.status\(403\)\.json\(\{ error: lockdown\.refusal/);
+  // And the per-key rule for the generic settings route.
+  assert.match(admin, /if \(lockdown\.isLocked\(key\)\) \{\s*\n\s*return res\.status\(403\)/);
+
+  // The panel learns the state from a response it already fetches, rather than
+  // adding a request of its own on every admin open.
+  assert.match(admin, /invites: await invites\.list\(\), inviteOnly: await invites\.inviteOnly\(\), lockdown: lockdown\.state\(\)/);
+  const panel = fs.readFileSync(path.join(__dirname, '..', 'public/js/admin.js'), 'utf8');
+  assert.match(panel, /window\.applyAdminLockdown\(data\.lockdown\)/);
+});