Cleaner up registration link creation. Don't show the dialog until when there is a valid link. Implement a global blur backdrop with nicer effect and proper scrollbar handling (avoiding layout shifting a bit). Use the global backdrop to ensure consistent visuals between authentication and the modal being shown, along with in/out transitions.

frontend/src/assets/style.css

@@ -337,10 +337,13 @@ th {
 .global-status {
   position: fixed;
   top: 1.5rem;
-  left: 50%;
-  transform: translateX(-50%);
+  left: 0;
+  right: 0;
+  margin: 0 auto;
   z-index: 1200;
-  min-width: min(520px, calc(100vw - 2rem));
+  width: fit-content;
+  min-width: min(520px, calc(100% - 2rem));
+  max-width: calc(100% - 2rem);
   display: none;
 }
 
@@ -377,10 +380,11 @@ th {
 
 .dialog-overlay {
   position: fixed;
-  inset: 0;
+  top: 0;
+  bottom: 0;
+  left: 0;
+  right: 0;
   background: transparent;
-  backdrop-filter: blur(.1rem) brightness(0.7);
-  -webkit-backdrop-filter: blur(.1rem) brightness(0.7);
   z-index: 1100;
   display: flex;
   align-items: center;
@@ -683,9 +687,41 @@ th {
   }
 }
 
-/* Auth iframe overlay styles */
+/* Global backdrop controlled by api.js ref-counting */
+body::before {
+  content: '';
+  position: fixed;
+  inset: 0;
+  z-index: 1099;
+  background: transparent;
+  backdrop-filter: blur(0) brightness(1);
+  -webkit-backdrop-filter: blur(0) brightness(1);
+  pointer-events: none;
+  visibility: hidden;
+  transition: all 0.2s ease-out;
+}
+
+body.has-backdrop::before {
+  -webkit-backdrop-filter: blur(.2rem) brightness(0.5);
+  backdrop-filter: blur(.2rem) brightness(0.5);
+  visibility: visible;
+}
+
+/* Prevent scrolling via html to avoid scrollbar layout shift */
+html:has(body.has-backdrop),
+html:has(#auth-iframe) {
+  overflow: clip;
+}
+
+body.has-backdrop {
+  overflow: auto;
+}
+
+/* Make fixed elements (toast, dialog) position relative to body, not viewport */
+/* This works because transform creates a new containing block for fixed children */
+body.has-backdrop,
 body:has(#auth-iframe) {
-  overflow: hidden;
+  transform: translateZ(0);
 }
 
 #auth-iframe {
@@ -698,8 +734,6 @@ body:has(#auth-iframe) {
   z-index: 9999;
   color-scheme: auto;
   background: transparent;
-  backdrop-filter: blur(.1rem) brightness(0.7);
-  -webkit-backdrop-filter: blur(.1rem) brightness(0.7);
 }
 
 .slot-machine {

frontend/src/components/RegistrationLinkModal.vue

@@ -1,5 +1,5 @@
 <template>
-  <div class="dialog-overlay" @keydown.esc.prevent="$emit('close')">
+  <div v-if="linkUrl" class="dialog-overlay no-backdrop" @keydown.esc.prevent="$emit('close')">
     <div class="device-dialog" role="dialog" aria-modal="true" aria-labelledby="regTitle">
       <div class="reg-header-row">
         <h2 id="regTitle" class="reg-title">
@@ -9,20 +9,6 @@
       </div>
 
       <div class="device-link-section">
-        <!-- Loading state -->
-        <div v-if="loading" class="loading-state">
-          <div class="spinner-small"></div>
-          <span>Generating registration link...</span>
-        </div>
-
-        <!-- Error state -->
-        <div v-else-if="error" class="error-state">
-          <p class="error-message">{{ error }}</p>
-          <button class="btn-secondary" @click="generateLink">Retry</button>
-        </div>
-
-        <!-- Success state with QR code and link -->
-        <template v-else-if="linkUrl">
         <p class="reg-help">
           Scan this QR code on the new device, or copy the link and open it there.
         </p>
@@ -36,7 +22,6 @@
         <p class="expiry-note" v-if="expiresAt">
           This link expires {{ formatDate(expiresAt).toLowerCase() }}.
         </p>
-        </template>
       </div>
 
       <div class="reg-actions">
@@ -47,9 +32,9 @@
 </template>
 
 <script setup>
-import { ref, onMounted } from 'vue'
+import { ref, onMounted, onUnmounted } from 'vue'
 import QRCodeDisplay from '@/components/QRCodeDisplay.vue'
-import { apiJson } from '@/utils/api'
+import { apiJson, holdGlobalBackdrop, releaseGlobalBackdrop } from '@/utils/api'
 import { formatDate } from '@/utils/helpers'
 
 const props = defineProps({
@@ -59,29 +44,20 @@ const props = defineProps({
 
 const emit = defineEmits(['close', 'copied'])
 
-const loading = ref(true)
-const error = ref(null)
 const linkUrl = ref(null)
 const expiresAt = ref(null)
 
 async function generateLink() {
-  loading.value = true
-  error.value = null
-  linkUrl.value = null
-  expiresAt.value = null
-
   try {
     const data = await apiJson(props.endpoint, { method: 'POST' })
     if (data.url) {
       linkUrl.value = data.url
       expiresAt.value = data.expires ? new Date(data.expires) : null
     } else {
-      error.value = data.detail || 'Failed to generate link'
+      emit('close')
     }
-  } catch (err) {
-    error.value = err.message || 'Failed to generate link'
-  } finally {
-    loading.value = false
+  } catch {
+    emit('close')
   }
 }
 
@@ -90,8 +66,15 @@ function onCopied() {
 }
 
 onMounted(() => {
+  // Hold backdrop before fetch to avoid gap if auth iframe shows
+  holdGlobalBackdrop()
   generateLink()
 })
+
+onUnmounted(() => {
+  // Release backdrop when modal closes
+  releaseGlobalBackdrop()
+})
 </script>
 
 <style scoped>
@@ -102,8 +85,11 @@ onMounted(() => {
 .device-dialog { background: var(--color-surface); padding: 1.25rem 1.25rem 1rem; border-radius: var(--radius-md); max-width: 480px; width: 100%; box-shadow: 0 6px 28px rgba(0,0,0,.25); }
 .reg-help { margin: .5rem 0 .75rem; font-size: .85rem; line-height: 1.4; text-align: center; color: var(--color-text-muted); }
 .reg-actions { display: flex; justify-content: flex-end; gap: .5rem; margin-top: 1rem; }
-.loading-state { display: flex; align-items: center; justify-content: center; gap: .5rem; padding: 2rem 0; color: var(--color-text-muted); }
-.error-state { text-align: center; padding: 1rem 0; }
-.error-message { color: var(--color-danger-text); margin-bottom: 1rem; }
 .expiry-note { font-size: .75rem; color: var(--color-text-muted); text-align: center; margin-top: .75rem; }
+
+/* Use global backdrop, not local */
+.dialog-overlay.no-backdrop {
+  backdrop-filter: none;
+  -webkit-backdrop-filter: none;
+}
 </style>

frontend/src/utils/api.js

@@ -49,6 +49,29 @@ let authPromise = null
 let authResolve = null
 let authReject = null
 
+// Global backdrop ref-count (works independently of Pinia store)
+let backdropHolders = 0
+
+/**
+ * Hold global backdrop (increment ref-count).
+ * Multiple callers can hold the backdrop; it only hides when all release.
+ */
+export function holdGlobalBackdrop() {
+  backdropHolders++
+  document.body.classList.add('has-backdrop')
+}
+
+/**
+ * Release global backdrop (decrement ref-count).
+ * Backdrop hides only when ref-count reaches zero.
+ */
+export function releaseGlobalBackdrop() {
+  backdropHolders = Math.max(0, backdropHolders - 1)
+  if (backdropHolders === 0) {
+    document.body.classList.remove('has-backdrop')
+  }
+}
+
 // Cache for auth iframe URL by mode
 const authIframeUrlCache = {}
 
@@ -93,6 +116,7 @@ export function isAuthIframeOpen() {
 /**
  * Show the authentication iframe and return a promise that resolves on success.
  * If an auth iframe is already open (from any source), hooks into its completion.
+ * Uses global backdrop system to avoid flicker between auth and caller's UI.
  * @param {string} iframeUrl - The URL for the iframe src
  * @returns {Promise<void>}
  * @throws {AuthCancelledError} - If authentication is cancelled by user
@@ -119,6 +143,9 @@ export function showAuthIframe(iframeUrl) {
   // Remove existing iframe if any
   hideAuthIframe()
 
+  // Hold global backdrop for auth iframe
+  holdGlobalBackdrop()
+
   // Create new iframe for authentication using src URL
   authIframe = document.createElement('iframe')
   authIframe.id = 'auth-iframe'
@@ -134,6 +161,7 @@ function hideAuthIframe() {
   if (authIframe) {
     authIframe.remove()
     authIframe = null
+    releaseGlobalBackdrop()
   }
 }