fix(dashboard): reduce SSE keepalive churn

.changeset/dispose-spawned-child-sessions.md

@@ -2,4 +2,4 @@
 "@runfusion/fusion": patch
 ---
 
-Dispose completed spawned child agent sessions so execution memory is released promptly after `fn_spawn_agent` children finish, keep artifact registry listing metadata-only so large inline artifacts are not loaded during agent execution, and bound structured tool-result log previews before serialization.
+Dispose completed spawned child agent sessions so execution memory is released promptly after `fn_spawn_agent` children finish, keep artifact registry listing metadata-only so large inline artifacts are not loaded during agent execution, bound structured tool-result log previews before serialization, and reduce dashboard SSE keepalive churn.

packages/dashboard/app/__tests__/sse-bus.test.ts

@@ -182,6 +182,36 @@ describe("sse-bus", () => {
     expect(MockEventSource.instances.length).toBe(countBeforeTimers);
   });
 
+  it("does not storm keepalive control requests for active local event streams", () => {
+    vi.useFakeTimers();
+    const originalFetch = window.fetch;
+    const fetchMock = vi.fn(() => Promise.resolve(new Response(null, { status: 204 })));
+    Object.defineProperty(window, "fetch", {
+      configurable: true,
+      writable: true,
+      value: fetchMock,
+    });
+    try {
+      const unsub = subscribeSse("/api/events", {});
+
+      expect(fetchMock).toHaveBeenCalledTimes(1);
+      vi.advanceTimersByTime(29_999);
+      expect(fetchMock).toHaveBeenCalledTimes(1);
+
+      vi.advanceTimersByTime(1);
+      expect(fetchMock).toHaveBeenCalledTimes(2);
+
+      unsub();
+    } finally {
+      Object.defineProperty(window, "fetch", {
+        configurable: true,
+        writable: true,
+        value: originalFetch,
+      });
+      vi.useRealTimers();
+    }
+  });
+
   it("reopens subscribed channel on pageshow even when event.persisted is false", () => {
     subscribeSse("/api/events?projectId=p1", {});
     expect(MockEventSource.instances).toHaveLength(1);

packages/dashboard/app/sse-bus.ts

@@ -16,8 +16,12 @@ type OpenListener = () => void;
 
 const HEARTBEAT_TIMEOUT_MS = 45_000;
 const RECONNECT_DELAY_MS = 3_000;
-const CLIENT_KEEPALIVE_INTERVAL_MS = 2_000;
-const CLIENT_KEEPALIVE_TIMEOUT_MS = 1_500;
+/*
+ * FNXC:DashboardSSE 2026-06-23-15:08:
+ * Dashboard SSE keepalive exists only to let the server reap abandoned browser streams. It must not create a visible storm of regular HTTP connections when the engine is off, so keep the liveness probe infrequent and let the server stale window absorb brief tab/network stalls.
+ */
+const CLIENT_KEEPALIVE_INTERVAL_MS = 30_000;
+const CLIENT_KEEPALIVE_TIMEOUT_MS = 5_000;
 const VISIBILITY_REOPEN_DEDUPE_MS = 1_000;
 const CLIENT_ID_STORAGE_KEY = "fusion:sse-client-id";
 

packages/dashboard/src/__tests__/sse.test.ts

@@ -338,7 +338,7 @@ describe("createSSE client cleanup", () => {
 
     expect(getActiveSSEConnections()).toBe(baseline + 1);
 
-    vi.advanceTimersByTime(4_999);
+    vi.advanceTimersByTime(74_999);
     expect(connection.res.end).not.toHaveBeenCalled();
     expect(getActiveSSEConnections()).toBe(baseline + 1);
 
@@ -353,14 +353,14 @@ describe("createSSE client cleanup", () => {
     const baseline = getActiveSSEConnections();
     const connection = openSseConnection("client-five");
 
-    vi.advanceTimersByTime(4_000);
+    vi.advanceTimersByTime(30_000);
     expect(markSSEClientAlive("client-five")).toBe(1);
 
-    vi.advanceTimersByTime(4_000);
+    vi.advanceTimersByTime(74_999);
     expect(connection.res.end).not.toHaveBeenCalled();
     expect(getActiveSSEConnections()).toBe(baseline + 1);
 
-    vi.advanceTimersByTime(1_000);
+    vi.advanceTimersByTime(1);
     expect(connection.res.end).toHaveBeenCalledTimes(1);
     expect(getActiveSSEConnections()).toBe(baseline);
   });

packages/dashboard/src/server.ts

@@ -963,7 +963,7 @@ export function createServer(store: TaskStore, options?: ServerOptions): ReturnT
       // attach to the same EventEmitter instance that the engine writes to,
       // rather than a separate store created by getOrCreateProjectStore.
       let scopedStore: TaskStore;
-      let agentStore;
+      let agentStore: AgentStore | undefined;
       let messageStore: MessageStore | undefined;
       let automationStore: AutomationStore | undefined;
       let scopedChatStore = chatStore;

packages/dashboard/src/sse.ts

@@ -19,7 +19,11 @@ let highWaterMark = 0;
 let nextConnectionId = 1;
 
 const SSE_CLIENT_ID_MAX_LENGTH = 128;
-const SSE_CLIENT_STALE_MS = 5_000;
+/*
+ * FNXC:DashboardSSE 2026-06-23-15:08:
+ * Client-side keepalive probes are intentionally infrequent to avoid a dashboard-only HTTP connection storm. Keep the server stale timer comfortably above that cadence so healthy streams are not reaped between probes while abandoned streams still self-clean.
+ */
+const SSE_CLIENT_STALE_MS = 75_000;
 // If a client's outbound buffer exceeds this, treat the connection as stuck
 // and close it. Without this, res.write() silently queues into res.outputData
 // for a paused/backgrounded client, and every store event for every entity