core: fix Tauri desktop app SSE connection timeout

- Add heartbeat events to /global/event and /event SSE endpoints
- Send server.heartbeat event every 30s to prevent WKWebView 60s timeout
- Fixes desktop app disconnecting from global events after 1 minute

packages/opencode/src/server/server.ts

@@ -139,8 +139,22 @@ export namespace Server {
               })
             }
             GlobalBus.on("event", handler)
+
+            // Send heartbeat every 30s to prevent WKWebView timeout (60s default)
+            const heartbeat = setInterval(() => {
+              stream.writeSSE({
+                data: JSON.stringify({
+                  payload: {
+                    type: "server.heartbeat",
+                    properties: {},
+                  },
+                }),
+              })
+            }, 30000)
+
             await new Promise<void>((resolve) => {
               stream.onAbort(() => {
+                clearInterval(heartbeat)
                 GlobalBus.off("event", handler)
                 resolve()
                 log.info("global event disconnected")
@@ -2470,8 +2484,20 @@ export namespace Server {
                 stream.close()
               }
             })
+
+            // Send heartbeat every 30s to prevent WKWebView timeout (60s default)
+            const heartbeat = setInterval(() => {
+              stream.writeSSE({
+                data: JSON.stringify({
+                  type: "server.heartbeat",
+                  properties: {},
+                }),
+              })
+            }, 30000)
+
             await new Promise<void>((resolve) => {
               stream.onAbort(() => {
+                clearInterval(heartbeat)
                 unsub()
                 resolve()
                 log.info("event disconnected")