fix(ui): debounce connection-lost banner so transient ws blips don't flash

The reconnect banner showed 'Connection lost'/'Reconnecting' instantly on every
socket close, even ones that recover in 100ms-2s (load spikes, Tailscale/relay
TCP resets). On a healthy node the drops are brief and self-healing, but each one
flashed a jarring banner, reading as constant instability.

Debounce the transient banner by 2.5s: only surface after the connection issue
persists past the grace window; hide immediately on recovery. Deliberate server
lifecycle transitions (restart/shutdown) bypass the debounce and still show at
once. A genuine persistent outage keeps isOffline true and surfaces after 2.5s.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

neode-ui/src/views/dashboard/ConnectionBanner.vue

@@ -1,9 +1,12 @@
 <template>
   <Teleport to="body">
-    <!-- Offline Banner -->
+    <!-- Lifecycle / Offline Banner.
+         Server restart/shutdown is deliberate → shown immediately. A plain
+         connection blip is debounced (showConnIssue) so transient sub-grace
+         reconnects don't flash. -->
     <Transition name="conn-banner">
       <div
-        v-if="isOffline && !store.isReconnecting && store.isAuthenticated"
+        v-if="(showLifecycle || showConnectionLost)"
         class="conn-banner-overlay"
       >
         <div class="path-option-card px-6 py-3 border-l-4 border-yellow-500 inline-flex items-center gap-2 text-yellow-200 shadow-2xl">
@@ -17,10 +20,10 @@
       </div>
     </Transition>
 
-    <!-- Reconnecting Banner -->
+    <!-- Reconnecting Banner (debounced) -->
     <Transition name="conn-banner">
       <div
-        v-if="store.isReconnecting && store.isAuthenticated"
+        v-if="showReconnecting"
         class="conn-banner-overlay"
       >
         <div class="path-option-card px-6 py-3 border-l-4 border-blue-500 inline-flex items-center gap-2 text-blue-200 shadow-2xl">
@@ -35,7 +38,7 @@
 </template>
 
 <script setup lang="ts">
-import { computed } from 'vue'
+import { computed, ref, watch, onUnmounted } from 'vue'
 import { useAppStore } from '@/stores/app'
 
 const store = useAppStore()
@@ -43,6 +46,58 @@ const store = useAppStore()
 const isOffline = computed(() => store.isOffline)
 const isRestarting = computed(() => store.isRestarting)
 const isShuttingDown = computed(() => store.isShuttingDown)
+
+// A deliberate server lifecycle transition (restart/shutdown) is real and
+// user-initiated — surface it immediately, no debounce.
+const isLifecycleTransition = computed(() => isRestarting.value || isShuttingDown.value)
+const showLifecycle = computed(() => isLifecycleTransition.value && store.isAuthenticated)
+
+// A plain connection blip (offline or reconnecting, not a lifecycle transition).
+// The overwhelming majority recover within a second or two (load spikes,
+// Tailscale/relay TCP resets), so showing the banner instantly makes a healthy
+// node read as unstable. Debounce: only surface after the issue persists past a
+// grace window; hide immediately on recovery.
+const hasConnIssue = computed(
+  () => (store.isReconnecting || isOffline.value) && !isLifecycleTransition.value
+)
+
+const SHOW_DELAY_MS = 2500
+const showConnIssue = ref(false)
+let pendingTimer: ReturnType<typeof setTimeout> | null = null
+
+function clearTimer() {
+  if (pendingTimer) {
+    clearTimeout(pendingTimer)
+    pendingTimer = null
+  }
+}
+
+watch(
+  hasConnIssue,
+  (issue) => {
+    clearTimer()
+    if (issue) {
+      pendingTimer = setTimeout(() => {
+        showConnIssue.value = true
+        pendingTimer = null
+      }, SHOW_DELAY_MS)
+    } else {
+      // Recovered before the grace window elapsed — hide at once.
+      showConnIssue.value = false
+    }
+  },
+  { immediate: true }
+)
+
+onUnmounted(clearTimer)
+
+// Debounced visual states the template renders.
+const showReconnecting = computed(
+  () => showConnIssue.value && store.isReconnecting && store.isAuthenticated
+)
+const showConnectionLost = computed(
+  () => showConnIssue.value && isOffline.value && !store.isReconnecting && store.isAuthenticated
+)
 </script>
 
 <style scoped>