Initial commit: Arb Pulse monolith with CI and optional Fly deploy.

Real-time BTC cross-exchange arbitrage detection (Kraken, Bybit, OKX, Binance)
with React dashboard, GitHub Actions CI, and documented Fly.io deploy workflow.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/interfaces/sse/sse.ts

@@ -0,0 +1,50 @@
+import type { Request, Response } from "express";
+import { config } from "../../infrastructure/config/config.js";
+import { createLogger } from "../../infrastructure/logging/logger.js";
+import type { ApplicationService } from "../../composition/application-service.js";
+
+const log = createLogger("sse");
+
+export class SseHub {
+  private clients = new Set<Response>();
+  private timer: NodeJS.Timeout | null = null;
+
+  constructor(private readonly app: ApplicationService) {}
+
+  start(): void {
+    this.timer = setInterval(() => this.broadcast(), config.broadcastMs);
+  }
+
+  stop(): void {
+    if (this.timer) clearInterval(this.timer);
+    for (const res of this.clients) res.end();
+    this.clients.clear();
+  }
+
+  handle(req: Request, res: Response): void {
+    res.writeHead(200, {
+      "Content-Type": "text/event-stream",
+      "Cache-Control": "no-cache, no-transform",
+      Connection: "keep-alive",
+      "X-Accel-Buffering": "no",
+    });
+    res.write(`retry: 2000\n\n`);
+    this.send(res, this.app.getSnapshot());
+    this.clients.add(res);
+    log.info(`client connected (${this.clients.size} total)`);
+
+    req.on("close", () => {
+      this.clients.delete(res);
+    });
+  }
+
+  private broadcast(): void {
+    if (this.clients.size === 0) return;
+    const snapshot = this.app.getSnapshot();
+    for (const res of this.clients) this.send(res, snapshot);
+  }
+
+  private send(res: Response, data: unknown): void {
+    res.write(`data: ${JSON.stringify(data)}\n\n`);
+  }
+}