(plan) convert original implement plan to mock api

app/api/stream/route.ts

@@ -0,0 +1,42 @@
+import { cluster, namespaces } from '@/lib/clusterMock'
+
+/**
+ * Mock stand-in for the real atlas `GET /api/stream`. Emits synthetic `topology` deltas on an
+ * interval and a keepalive comment frame, matching the SSE shape the frontend expects — no real
+ * informer, no real cluster.
+ */
+export async function GET(req: Request) {
+  const encoder = new TextEncoder()
+  let seq = cluster.generation
+
+  const stream = new ReadableStream({
+    start(controller) {
+      const send = (event: string, data: unknown) => {
+        controller.enqueue(encoder.encode(`event: ${event}\nid: ${seq++}\ndata: ${JSON.stringify(data)}\n\n`))
+      }
+
+      const keepalive = setInterval(() => {
+        controller.enqueue(encoder.encode(': keepalive\n\n'))
+      }, 30_000)
+
+      const delta = setInterval(() => {
+        const ns = namespaces[Math.floor(Math.random() * namespaces.length)]
+        send('topology', { namespace: ns.name, running: ns.running, total: ns.total })
+      }, 5_000)
+
+      req.signal.addEventListener('abort', () => {
+        clearInterval(keepalive)
+        clearInterval(delta)
+        controller.close()
+      })
+    },
+  })
+
+  return new Response(stream, {
+    headers: {
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      Connection: 'keep-alive',
+    },
+  })
+}