feat: add background monitor service for payments and escrows

- Long-running service polls /api/cron/monitor-payments every 15s
- Exponential backoff on errors (up to 5min)
- 30s startup delay for Next.js boot
- Runs alongside Next.js via start.sh with signal forwarding
- Replaces Vercel cron config (doesn't work on Railway)
- Only logs when there's actual activity

Author: ralyodio

scripts/monitor-service.ts

@@ -0,0 +1,104 @@
+#!/usr/bin/env -S npx tsx
+/**
+ * Payment & Escrow Monitor Service
+ * 
+ * Long-running background service that polls the monitor endpoint.
+ * Runs alongside the Next.js app on Railway.
+ * 
+ * Interval: 15 seconds (configurable via MONITOR_INTERVAL_MS)
+ */
+
+const APP_URL = process.env.NEXT_PUBLIC_APP_URL || process.env.APP_URL || "http://localhost:3000";
+const API_KEY = process.env.INTERNAL_API_KEY || "";
+const INTERVAL_MS = parseInt(process.env.MONITOR_INTERVAL_MS || "15000");
+const STARTUP_DELAY_MS = parseInt(process.env.MONITOR_STARTUP_DELAY_MS || "30000");
+
+let running = true;
+let consecutiveErrors = 0;
+const MAX_BACKOFF_MS = 5 * 60 * 1000; // 5 min max backoff
+
+async function runCycle(): Promise<void> {
+  try {
+    const controller = new AbortController();
+    const timeout = setTimeout(() => controller.abort(), 30000);
+
+    const res = await fetch(`${APP_URL}/api/cron/monitor-payments`, {
+      method: "GET",
+      headers: { Authorization: `Bearer ${API_KEY}` },
+      signal: controller.signal,
+    });
+
+    clearTimeout(timeout);
+
+    if (res.ok) {
+      const data = await res.json();
+      consecutiveErrors = 0;
+
+      // Only log if something happened
+      const escrow = data.escrow || {};
+      const stats = data.stats || {};
+      const ln = data.lightning || {};
+      const inv = data.invoices || {};
+
+      const activity = (escrow.funded || 0) + (escrow.expired || 0) + 
+        (stats.confirmed || 0) + (ln.settled || 0) + (inv.detected || 0);
+
+      if (activity > 0) {
+        console.log(`[Monitor] Activity:`, JSON.stringify({
+          escrow: escrow.funded || escrow.expired ? escrow : undefined,
+          payments: stats.confirmed ? stats : undefined,
+          lightning: ln.settled ? ln : undefined,
+          invoices: inv.detected ? inv : undefined,
+        }));
+      }
+    } else {
+      const text = await res.text().catch(() => "");
+      console.error(`[Monitor] HTTP ${res.status}: ${text.slice(0, 200)}`);
+      consecutiveErrors++;
+    }
+  } catch (err: any) {
+    if (err.name === "AbortError") {
+      console.error("[Monitor] Request timed out (30s)");
+    } else {
+      console.error(`[Monitor] Error: ${err.message}`);
+    }
+    consecutiveErrors++;
+  }
+}
+
+async function main() {
+  console.log(`[Monitor] Starting payment monitor service`);
+  console.log(`[Monitor] URL: ${APP_URL}/api/cron/monitor-payments`);
+  console.log(`[Monitor] Interval: ${INTERVAL_MS}ms, startup delay: ${STARTUP_DELAY_MS}ms`);
+
+  if (!API_KEY) {
+    console.error("[Monitor] WARNING: INTERNAL_API_KEY not set — requests will be unauthorized");
+  }
+
+  // Wait for the app to start up
+  await new Promise(r => setTimeout(r, STARTUP_DELAY_MS));
+  console.log("[Monitor] Startup delay complete, beginning monitor cycles");
+
+  while (running) {
+    await runCycle();
+
+    // Exponential backoff on consecutive errors (15s → 30s → 60s → ... → 5min)
+    const backoff = consecutiveErrors > 0
+      ? Math.min(INTERVAL_MS * Math.pow(2, consecutiveErrors - 1), MAX_BACKOFF_MS)
+      : INTERVAL_MS;
+
+    if (backoff > INTERVAL_MS) {
+      console.log(`[Monitor] Backing off: ${Math.round(backoff / 1000)}s (${consecutiveErrors} consecutive errors)`);
+    }
+
+    await new Promise(r => setTimeout(r, backoff));
+  }
+}
+
+process.on("SIGTERM", () => { running = false; console.log("[Monitor] Shutting down..."); });
+process.on("SIGINT", () => { running = false; console.log("[Monitor] Shutting down..."); });
+
+main().catch(err => {
+  console.error("[Monitor] Fatal:", err);
+  process.exit(1);
+});

scripts/start.sh

@@ -1,6 +1,29 @@
 #!/bin/sh
-# Railway start script
+# Railway start script — runs Next.js app + payment monitor service
 
-# Keep process resilient and avoid frequent OOM exits under production load
 export NODE_OPTIONS="--max-old-space-size=1024 --unhandled-rejections=warn"
-exec pnpm start
+
+# Start the monitor service in the background
+npx tsx scripts/monitor-service.ts &
+MONITOR_PID=$!
+
+# Trap signals to clean up both processes
+cleanup() {
+  echo "[start.sh] Shutting down..."
+  kill $MONITOR_PID 2>/dev/null
+  wait $MONITOR_PID 2>/dev/null
+  exit 0
+}
+trap cleanup SIGTERM SIGINT
+
+# Start Next.js in the foreground
+pnpm start &
+NEXT_PID=$!
+
+# Wait for either to exit
+wait $NEXT_PID
+EXIT_CODE=$?
+
+# If Next.js dies, kill the monitor too
+kill $MONITOR_PID 2>/dev/null
+exit $EXIT_CODE