feat(slack): add HTTP receiver webhook mode (#1143) - thanks @jdrhyne

Co-authored-by: Jonathan Rhyne <jdrhyne@users.noreply.github.com>

src/slack/http/registry.ts

@@ -0,0 +1,45 @@
+import type { IncomingMessage, ServerResponse } from "node:http";
+
+export type SlackHttpRequestHandler = (
+  req: IncomingMessage,
+  res: ServerResponse,
+) => Promise<void> | void;
+
+type RegisterSlackHttpHandlerArgs = {
+  path?: string | null;
+  handler: SlackHttpRequestHandler;
+  log?: (message: string) => void;
+  accountId?: string;
+};
+
+const slackHttpRoutes = new Map<string, SlackHttpRequestHandler>();
+
+export function normalizeSlackWebhookPath(path?: string | null): string {
+  const trimmed = path?.trim();
+  if (!trimmed) return "/slack/events";
+  return trimmed.startsWith("/") ? trimmed : `/${trimmed}`;
+}
+
+export function registerSlackHttpHandler(params: RegisterSlackHttpHandlerArgs): () => void {
+  const normalizedPath = normalizeSlackWebhookPath(params.path);
+  if (slackHttpRoutes.has(normalizedPath)) {
+    const suffix = params.accountId ? ` for account "${params.accountId}"` : "";
+    params.log?.(`slack: webhook path ${normalizedPath} already registered${suffix}`);
+    return () => {};
+  }
+  slackHttpRoutes.set(normalizedPath, params.handler);
+  return () => {
+    slackHttpRoutes.delete(normalizedPath);
+  };
+}
+
+export async function handleSlackHttpRequest(
+  req: IncomingMessage,
+  res: ServerResponse,
+): Promise<boolean> {
+  const url = new URL(req.url ?? "/", "http://localhost");
+  const handler = slackHttpRoutes.get(url.pathname);
+  if (!handler) return false;
+  await handler(req, res);
+  return true;
+}