feat(dashboard): add Zellij unavailable warning banner

dashboard/components/App.js

@@ -1,5 +1,5 @@
 import { html, useState, useEffect, useCallback, useMemo, useRef } from '../lib/preact.js';
-import { API_STATE, API_STREAM, API_DISMISS, API_DISMISS_DEAD, API_RESPOND, API_CONVERSATION, POLL_MS, fetchWithTimeout } from '../utils/api.js';
+import { API_STATE, API_STREAM, API_DISMISS, API_DISMISS_DEAD, API_RESPOND, API_CONVERSATION, API_HEALTH, POLL_MS, fetchWithTimeout } from '../utils/api.js';
 import { groupSessionsByProject } from '../utils/status.js';
 import { Sidebar } from './Sidebar.js';
 import { SessionCard } from './SessionCard.js';
@@ -20,6 +20,9 @@ export function App() {
   const [sseConnected, setSseConnected] = useState(false);
   const [deadSessionsCollapsed, setDeadSessionsCollapsed] = useState(true);
   const [spawnModalOpen, setSpawnModalOpen] = useState(false);
+  const [zellijAvailable, setZellijAvailable] = useState(true);
+  const [newlySpawnedIds, setNewlySpawnedIds] = useState(new Set());
+  const pendingSpawnIdsRef = useRef(new Set());
 
   // Background conversation refresh with error tracking
   const refreshConversationSilent = useCallback(async (sessionId, projectDir, agent = 'claude') => {
@@ -71,6 +74,34 @@ export function App() {
       }
     }
 
+    // Check for newly spawned sessions matching pending spawn IDs
+    if (pendingSpawnIdsRef.current.size > 0) {
+      const matched = new Set();
+      for (const session of newSessions) {
+        if (session.spawn_id && pendingSpawnIdsRef.current.has(session.spawn_id)) {
+          matched.add(session.session_id);
+          pendingSpawnIdsRef.current.delete(session.spawn_id);
+        }
+      }
+      if (matched.size > 0) {
+        setNewlySpawnedIds(prev => {
+          const next = new Set(prev);
+          for (const id of matched) next.add(id);
+          return next;
+        });
+        // Auto-clear highlight after animation duration (2.5s)
+        for (const id of matched) {
+          setTimeout(() => {
+            setNewlySpawnedIds(prev => {
+              const next = new Set(prev);
+              next.delete(id);
+              return next;
+            });
+          }, 2500);
+        }
+      }
+    }
+
     // Clean up conversation cache for sessions that no longer exist
     setConversations(prev => {
       const activeIds = Object.keys(prev).filter(id => newSessionIds.has(id));
@@ -303,6 +334,25 @@ export function App() {
     return () => clearInterval(interval);
   }, [fetchState, sseConnected]);
 
+  // Poll Zellij health status
+  useEffect(() => {
+    const checkHealth = async () => {
+      try {
+        const response = await fetchWithTimeout(API_HEALTH);
+        if (response.ok) {
+          const data = await response.json();
+          setZellijAvailable(data.zellij_available);
+        }
+      } catch {
+        // Server unreachable - handled by state fetch error
+      }
+    };
+
+    checkHealth();
+    const interval = setInterval(checkHealth, 30000);
+    return () => clearInterval(interval);
+  }, []);
+
   // Group sessions by project
   const projectGroups = groupSessionsByProject(sessions);
 
@@ -353,6 +403,9 @@ export function App() {
   const handleSpawnResult = useCallback((result) => {
     if (result.success) {
       showToast(`${result.agentType} agent spawned for ${result.project}`, 'success');
+      if (result.spawnId) {
+        pendingSpawnIdsRef.current.add(result.spawnId);
+      }
     } else if (result.error) {
       showToast(result.error, 'error');
     }
@@ -419,7 +472,8 @@ export function App() {
             })()}
           </div>
           <button
-            class="rounded-lg border border-active/40 bg-active/12 px-3 py-2 text-sm font-medium text-active transition-colors hover:bg-active/20"
+            disabled=${!zellijAvailable}
+            class="rounded-lg border border-active/40 bg-active/12 px-3 py-2 text-sm font-medium text-active transition-colors hover:bg-active/20 ${!zellijAvailable ? 'opacity-50 cursor-not-allowed' : ''}"
             onClick=${() => setSpawnModalOpen(true)}
           >
             + New Agent
@@ -427,6 +481,13 @@ export function App() {
         </div>
       </header>
 
+      ${!zellijAvailable && html`
+        <div class="border-b border-attention/50 bg-attention/10 px-6 py-2 text-sm text-attention">
+          <span class="font-medium">Zellij session not found.</span>
+          ${' '}Agent spawning is unavailable. Start Zellij with: <code class="rounded bg-attention/15 px-1.5 py-0.5 font-mono text-micro">zellij attach infra</code>
+        </div>
+      `}
+
       <main class="px-6 pb-6 pt-6">
         ${loading ? html`
           <div class="glass-panel animate-fade-in-up flex items-center justify-center rounded-2xl py-24">
@@ -454,6 +515,7 @@ export function App() {
                   onFetchConversation=${fetchConversation}
                   onRespond=${respondToSession}
                   onDismiss=${dismissSession}
+                  isNewlySpawned=${newlySpawnedIds.has(session.session_id)}
                 />
               `)}
             </div>