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/application/use-cases/process-order-book-update.ts

@@ -0,0 +1,21 @@
+import type { OrderBook } from "../../domain/entities/index.js";
+import type { ArbitrageEngine } from "../../domain/services/arbitrage-engine.js";
+
+export interface FeedRecorderPort {
+  record(book: OrderBook): void;
+}
+
+/** Hot path: record optional NDJSON, then drive detection on the updated book. */
+export class ProcessOrderBookUpdate {
+  constructor(
+    private readonly engine: ArbitrageEngine,
+    private readonly recorder: FeedRecorderPort,
+    private readonly isExchangeActive: (exchange: OrderBook["exchange"]) => boolean,
+  ) {}
+
+  run(book: OrderBook): void {
+    if (!this.isExchangeActive(book.exchange)) return;
+    this.recorder.record(book);
+    this.engine.onBook(book);
+  }
+}