fix: onboarding 401 redirect, glass card rendering bugs

- rpc-client: don't redirect to /login on 401 during onboarding flow,
  which caused session expired kicks on fresh installs
- style.css: add translateZ(0) + isolation:isolate to glass-card,
  glass-strong, path-option-card to fix Chromium compositor bug where
  backdrop-filter + animated fixed overlays cause black rectangles
- App.vue: pause background animations when tab hidden, force
  compositor layer rebuild on tab return to prevent stale renders

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/App.vue

@@ -168,7 +168,28 @@ const isReady = ref(false)
  * - User has already seen the intro
  * - User is on a direct route (refresh/bookmark)
  */
+// Fix Chromium backdrop-filter rendering bug: when tab loses/regains focus,
+// the compositor fails to repaint backdrop-filter layers over animated
+// fixed-position overlays (body::before/after with mix-blend-mode).
+// On return: strip backdrop-filter via class, wait a frame, then restore.
+function onVisibilityChange() {
+  if (document.hidden) {
+    document.documentElement.classList.add('tab-hidden')
+  } else {
+    // Step 1: kill all backdrop-filters (forces compositor to drop those layers)
+    document.documentElement.classList.add('no-backdrop')
+    document.documentElement.classList.remove('tab-hidden')
+    // Step 2: next frame, re-enable (compositor builds fresh layers)
+    requestAnimationFrame(() => {
+      requestAnimationFrame(() => {
+        document.documentElement.classList.remove('no-backdrop')
+      })
+    })
+  }
+}
+
 onMounted(async () => {
+  document.addEventListener('visibilitychange', onVisibilityChange)
   window.addEventListener('keydown', onKeyDown, true)
   window.addEventListener('mousemove', onUserActivity)
   window.addEventListener('mousedown', onUserActivity)
@@ -196,6 +217,7 @@ onMounted(async () => {
 })
 
 onBeforeUnmount(() => {
+  document.removeEventListener('visibilitychange', onVisibilityChange)
   window.removeEventListener('keydown', onKeyDown, true)
   window.removeEventListener('mousemove', onUserActivity)
   window.removeEventListener('mousedown', onUserActivity)

neode-ui/src/api/rpc-client.ts

@@ -62,7 +62,9 @@ class RPCClient {
           // Use a single shared timeout to prevent redirect storms when
           // multiple parallel requests all get 401 at once
           if (response.status === 401 && method !== 'auth.login') {
-            if (!RPCClient._sessionExpiredRedirecting) {
+            // Don't redirect during onboarding — those endpoints are unauthenticated
+            const isOnboarding = window.location.pathname.startsWith('/onboarding')
+            if (!isOnboarding && !RPCClient._sessionExpiredRedirecting) {
               RPCClient._sessionExpiredRedirecting = true
               setTimeout(() => {
                 window.location.href = '/login'

neode-ui/src/style.css

@@ -115,14 +115,18 @@ input[type="radio"]:active + * {
     -webkit-backdrop-filter: blur(18px);
     border: 1px solid rgba(255, 255, 255, 0.18);
     box-shadow: 0 8px 24px rgba(0, 0, 0, 0.45);
+    transform: translateZ(0);
+    isolation: isolate;
   }
-  
+
   .glass-strong {
     background-color: rgba(0, 0, 0, 0.35);
     backdrop-filter: blur(24px);
     -webkit-backdrop-filter: blur(24px);
     border: 1px solid rgba(255, 255, 255, 0.18);
     box-shadow: 0 8px 24px rgba(0, 0, 0, 0.45);
+    transform: translateZ(0);
+    isolation: isolate;
   }
   
   .glass-card {
@@ -134,6 +138,11 @@ input[type="radio"]:active + * {
     border-radius: 1rem;
     overflow-x: hidden;
     overflow-y: visible;
+    /* Fix Chromium compositor bug: backdrop-filter + fixed animated overlays
+       causes cards to render as black rectangles on scroll/tab-switch.
+       Own layer + isolation prevents stacking context confusion. */
+    transform: translateZ(0);
+    isolation: isolate;
   }
 
   /* Mode switcher - sidebar toggle */
@@ -767,6 +776,8 @@ input[type="radio"]:active + * {
     cursor: pointer;
     transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1), background-color 0.2s ease, box-shadow 0.3s ease;
     border: none;
+    transform: translateZ(0);
+    isolation: isolate;
   }
 
   .path-option-card:active {
@@ -1175,6 +1186,23 @@ body::after {
   animation-fill-mode: backwards;
 }
 
+/* Pause background animations when tab is hidden to prevent
+   Chromium compositor from corrupting backdrop-filter layers on tab return */
+html.tab-hidden body::before,
+html.tab-hidden body::after,
+html.tab-hidden::before {
+  animation-play-state: paused !important;
+  will-change: auto !important;
+}
+
+/* Strip all backdrop-filters to force compositor layer rebuild on tab return */
+html.no-backdrop *,
+html.no-backdrop *::before,
+html.no-backdrop *::after {
+  backdrop-filter: none !important;
+  -webkit-backdrop-filter: none !important;
+}
+
 /* Dashboard: full viewport width, no letterboxing, no body scroll */
 body.dashboard-active {
   overflow: hidden;