feat(mcp): add guided construction workflows

apps/editor/app/api/scenes/[id]/events/route.ts

@@ -0,0 +1,101 @@
+import { NextResponse } from 'next/server'
+import { getSceneStore } from '@/lib/scene-store-server'
+
+export const dynamic = 'force-dynamic'
+export const runtime = 'nodejs'
+
+type RouteParams = { params: Promise<{ id: string }> }
+
+const POLL_MS = 250
+const HEARTBEAT_MS = 15_000
+const MAX_EVENTS_PER_POLL = 50
+
+export async function GET(request: Request, { params }: RouteParams) {
+  const { id } = await params
+  const store = await getSceneStore()
+
+  if (!store.listSceneEvents) {
+    return NextResponse.json({ error: 'scene_events_unavailable' }, { status: 501 })
+  }
+
+  const scene = await store.load(id)
+  if (!scene) {
+    return NextResponse.json({ error: 'not_found' }, { status: 404 })
+  }
+
+  const url = new URL(request.url)
+  const afterFromQuery = Number.parseInt(url.searchParams.get('after') ?? '0', 10)
+  const afterFromHeader = Number.parseInt(request.headers.get('Last-Event-ID') ?? '0', 10)
+  let cursor = Math.max(
+    0,
+    Number.isFinite(afterFromQuery) ? afterFromQuery : 0,
+    Number.isFinite(afterFromHeader) ? afterFromHeader : 0,
+  )
+
+  const encoder = new TextEncoder()
+  let closed = false
+  let pollTimer: ReturnType<typeof setTimeout> | undefined
+  let heartbeatTimer: ReturnType<typeof setInterval> | undefined
+
+  const stream = new ReadableStream<Uint8Array>({
+    start(controller) {
+      const enqueue = (chunk: string) => {
+        if (!closed) controller.enqueue(encoder.encode(chunk))
+      }
+
+      const close = () => {
+        if (closed) return
+        closed = true
+        if (pollTimer) clearTimeout(pollTimer)
+        if (heartbeatTimer) clearInterval(heartbeatTimer)
+        try {
+          controller.close()
+        } catch {
+          // The client may have already closed the stream.
+        }
+      }
+
+      request.signal.addEventListener('abort', close, { once: true })
+      enqueue('retry: 1000\n\n')
+
+      const poll = async () => {
+        if (closed) return
+        try {
+          const events = await store.listSceneEvents!(id, {
+            afterEventId: cursor,
+            limit: MAX_EVENTS_PER_POLL,
+          })
+          for (const event of events) {
+            cursor = event.eventId
+            enqueue(`id: ${event.eventId}\n`)
+            enqueue('event: scene\n')
+            enqueue(`data: ${JSON.stringify(event)}\n\n`)
+          }
+        } catch (error) {
+          const message = error instanceof Error ? error.message : String(error)
+          enqueue('event: error\n')
+          enqueue(`data: ${JSON.stringify({ message })}\n\n`)
+        } finally {
+          if (!closed) pollTimer = setTimeout(poll, POLL_MS)
+        }
+      }
+
+      heartbeatTimer = setInterval(() => enqueue(': keepalive\n\n'), HEARTBEAT_MS)
+      void poll()
+    },
+    cancel() {
+      closed = true
+      if (pollTimer) clearTimeout(pollTimer)
+      if (heartbeatTimer) clearInterval(heartbeatTimer)
+    },
+  })
+
+  return new Response(stream, {
+    headers: {
+      'Cache-Control': 'no-cache, no-transform',
+      Connection: 'keep-alive',
+      'Content-Type': 'text/event-stream; charset=utf-8',
+      'X-Accel-Buffering': 'no',
+    },
+  })
+}