feat: add webhook delivery module with retry and backoff

apps/api/src/lib/webhook-delivery.ts

@@ -0,0 +1,61 @@
+interface DeliveryOptions {
+  maxRetries?: number;
+  initialDelayMs?: number;
+  timeoutMs?: number;
+}
+
+interface DeliveryResult {
+  success: boolean;
+  statusCode?: number;
+  error?: string;
+  attempts: number;
+}
+
+export async function deliverWebhook(
+  url: string,
+  authHeader: string,
+  events: Record<string, unknown>[],
+  options: DeliveryOptions = {},
+): Promise<DeliveryResult> {
+  const { maxRetries = 3, initialDelayMs = 1000, timeoutMs = 30_000 } = options;
+
+  const payload = JSON.stringify({
+    source: "snapotter",
+    version: "1",
+    events,
+  });
+
+  const headers: Record<string, string> = { "Content-Type": "application/json" };
+  if (authHeader) headers["Authorization"] = authHeader;
+
+  let lastError: string | undefined;
+  for (let attempt = 0; attempt <= maxRetries; attempt++) {
+    if (attempt > 0) {
+      const delay = initialDelayMs * 2 ** (attempt - 1);
+      await new Promise((r) => setTimeout(r, delay));
+    }
+
+    try {
+      const response = await fetch(url, {
+        method: "POST",
+        headers,
+        body: payload,
+        signal: AbortSignal.timeout(timeoutMs),
+      });
+
+      if (response.ok) {
+        return { success: true, statusCode: response.status, attempts: attempt + 1 };
+      }
+
+      lastError = `HTTP ${response.status}`;
+      // Don't retry 4xx errors (client errors = won't succeed on retry)
+      if (response.status >= 400 && response.status < 500) {
+        return { success: false, statusCode: response.status, error: lastError, attempts: attempt + 1 };
+      }
+    } catch (err) {
+      lastError = err instanceof Error ? err.message : String(err);
+    }
+  }
+
+  return { success: false, error: lastError, attempts: maxRetries + 1 };
+}