fix(dashboard): unstick Active Agents panel cards from "Connecting..."

Agents in `active` state without a current taskId had no SSE to attach
to, but the card still rendered "Connecting..." — implying a network
state that never resolves. Branch on taskId first: idle agents show
"Idle — no task assigned"; running-without-task shows "Starting...".

Also fix a related SSE multiplexer race: subscribers joining a channel
that had already opened never got an onOpen callback (EventSource only
fires `open` once), so they sat at isConnected=false forever whenever
another component was already streaming the same URL. Fire onOpen on a
microtask for late-joiners.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/ActiveAgentsPanel.tsx

@@ -98,7 +98,13 @@ function LiveAgentCard({ agent, projectId, onSelect, onOpenTaskLogs }: LiveAgent
       <div className="live-agent-card-transcript">
         {entries.length === 0 ? (
           <div className="live-agent-card-empty">
-            {currentStep ? (
+            {!agent.taskId ? (
+              // "active" agents that aren't currently working a task have no
+              // SSE stream to attach to; useLiveTranscript bails out with
+              // isConnected=false. Showing "Connecting..." here is misleading
+              // — the agent is just idle.
+              <span>{agent.state === "running" ? "Starting..." : "Idle — no task assigned"}</span>
+            ) : currentStep ? (
               <>
                 <div className="live-agent-card-status">
                   Step {stepNumber}

packages/dashboard/app/components/__tests__/ActiveAgentsPanel.test.tsx

@@ -119,6 +119,48 @@ describe("ActiveAgentsPanel", () => {
     expect(screen.getByText("Waiting for output...")).toBeInTheDocument();
   });
 
+  it("shows idle copy (not 'Connecting...') when an active agent has no taskId", async () => {
+    mockUseLiveTranscript.mockReturnValue({
+      entries: [],
+      isConnected: false,
+    });
+
+    const mockAgent: Agent = {
+      id: "agent-001",
+      name: "Test Agent",
+      role: "executor",
+      state: "active",
+      // taskId intentionally omitted — agent is available but not running
+      lastHeartbeatAt: new Date().toISOString(),
+    } as Agent;
+
+    render(<ActiveAgentsPanel agents={[mockAgent]} />);
+
+    expect(screen.getByText("Idle — no task assigned")).toBeInTheDocument();
+    expect(screen.queryByText("Connecting...")).toBeNull();
+  });
+
+  it("shows 'Starting...' for running agents that haven't picked up a task yet", async () => {
+    mockUseLiveTranscript.mockReturnValue({
+      entries: [],
+      isConnected: false,
+    });
+
+    const mockAgent: Agent = {
+      id: "agent-001",
+      name: "Test Agent",
+      role: "executor",
+      state: "running",
+      // taskId intentionally omitted — race between state flip and task bind
+      lastHeartbeatAt: new Date().toISOString(),
+    } as Agent;
+
+    render(<ActiveAgentsPanel agents={[mockAgent]} />);
+
+    expect(screen.getByText("Starting...")).toBeInTheDocument();
+    expect(screen.queryByText("Connecting...")).toBeNull();
+  });
+
   it("renders multiple agent cards with separate transcript streams", async () => {
     mockUseLiveTranscript
       .mockReturnValueOnce({

packages/dashboard/app/sse-bus.ts

@@ -383,9 +383,22 @@ export function subscribeSse(url: string, sub: SseSubscription = {}): () => void
   }
 
   channel.subscribers.add(subscriber);
+  const wasAlreadyOpen = !!channel.es && channel.hasOpenedOnce;
   openChannel(channel);
   reattachNativeListeners(channel);
 
+  // Subscribers joining a channel that already opened never see another
+  // `open` event from EventSource, so fire onOpen for them on a microtask
+  // (microtask, not sync, so the caller finishes wiring before state
+  // updates land).
+  if (wasAlreadyOpen) {
+    queueMicrotask(() => {
+      if (channel.subscribers.has(subscriber)) {
+        subscriber.onOpen?.();
+      }
+    });
+  }
+
   let active = true;
   return () => {
     if (!active) return;