diff --git a/public/js/accountBoundary.js b/public/js/accountBoundary.js
index ab42fe74..c1ea5fd4 100644
--- a/public/js/accountBoundary.js
+++ b/public/js/accountBoundary.js
@@ -14,8 +14,14 @@
   function recoverSignIn() {
     signInRequired = true;
     freeze();
+    // Say what happened, not only that something did. This fires when the page
+    // is bound to one account and the session belongs to another — switching
+    // accounts on a shared device is the ordinary cause, and it reads as a
+    // failure when the message does not name it.
     document.querySelector('#account-recovery p').textContent =
-        'Your saved credentials no longer match this session. Sign in again in a fresh page.';
+        'This page was opened for a different account than the one now signed in. ' +
+        'That is a safeguard, not an error: nothing is lost, and no data from either ' +
+        'account has been mixed. Start a fresh session to continue.';
     document.querySelector('#account-recovery button').textContent = 'Sign in again';
   }
   function read() {
diff --git a/public/js/auth.js b/public/js/auth.js
index 0ae1d303..f6b9a470 100644
--- a/public/js/auth.js
+++ b/public/js/auth.js
@@ -191,9 +191,21 @@ document.addEventListener('DOMContentLoaded', function() {
   } catch (e) {}
   var ssoButton = document.getElementById('btn-sso');
   if (ssoButton) ssoButton.addEventListener('click', async function(e) {
-    if (!e.isTrusted || authenticationPending || boundary.blocked()) { e.preventDefault(); return; }
+    // A frozen realm cannot start a login, and silently doing nothing reads as
+    // "SSO is broken" — it is the account boundary holding, not a failure. Say
+    // so, and point at the one control that clears it.
+    if (boundary.blocked()) {
+      e.preventDefault();
+      showToast('This page is locked to a different account. Tap "Sign in again" to start a fresh session, then use SSO.', 'error');
+      return;
+    }
+    if (!e.isTrusted || authenticationPending) { e.preventDefault(); return; }
     boundary.capture(); // Detect a replaced sibling session before capturing credentials.
-    if (boundary.blocked()) { e.preventDefault(); return; }
+    if (boundary.blocked()) {
+      e.preventDefault();
+      showToast('This page is locked to a different account. Tap "Sign in again" to start a fresh session, then use SSO.', 'error');
+      return;
+    }
     // No owner marker can also mean bootstrap failed with an old cookie still
     // valid. Every SSO start must prove cookie absence before issuing intent.
     e.preventDefault();