(plan) convert original implement plan to mock api

app/api/chat/route.ts

@@ -0,0 +1,50 @@
+/**
+ * Mock stand-in for the real atlas `POST /api/chat`. Streams the same SSE event shape
+ * (`queue` → `reasoning` → `content` → `done`) as the real endpoint would, but replays a
+ * canned reply instead of calling vLLM — no rate limiting, no budget, no real model.
+ */
+const REPLY_REASONING =
+  'The user is asking about a gap in the wave column display. Argo CD sync waves are integers used purely for ordering; there is no requirement that they be contiguous. The cluster uses 0,1,2,3,5,6,7,8. This is normal and usually happens when a wave is retired or intentionally reserved.'
+
+const REPLY =
+  'Wave 4 is empty. Waves are sort keys, not a sequence — Argo orders by value and skips gaps, so 3 is followed directly by 5. Nothing is missing.'
+
+const wait = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms))
+
+export async function POST() {
+  const encoder = new TextEncoder()
+
+  const stream = new ReadableStream({
+    async start(controller) {
+      const send = (type: string, payload: Record<string, unknown> = {}) => {
+        controller.enqueue(encoder.encode(`data: ${JSON.stringify({ type, ...payload })}\n\n`))
+      }
+
+      for (let position = 3; position > 0; position--) {
+        send('queue', { position })
+        await wait(500)
+      }
+
+      send('reasoning', { text: REPLY_REASONING })
+      await wait(200)
+
+      let i = 0
+      while (i < REPLY.length) {
+        i += 3
+        send('content', { text: REPLY.slice(0, i) })
+        await wait(40)
+      }
+
+      send('done')
+      controller.close()
+    },
+  })
+
+  return new Response(stream, {
+    headers: {
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      Connection: 'keep-alive',
+    },
+  })
+}