feat(channels): add Synology Chat native channel (#23012)

* feat(channels): add Synology Chat native channel

Webhook-based integration with Synology NAS Chat (DSM 7+).
Supports outgoing webhooks, incoming messages, multi-account,
DM policies, rate limiting, and input sanitization.

- HMAC-based constant-time token validation
- Configurable SSL verification (allowInsecureSsl) for self-signed NAS certs
- 54 unit tests across 5 test suites
- Follows the same ChannelPlugin pattern as LINE/Discord/Telegram

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat(synology-chat): add pairing, warnings, messaging, agent hints

- Enable media capability (file_url already supported by client)
- Add pairing.notifyApproval to message approved users
- Add security.collectWarnings for missing token/URL, insecure SSL, open DM policy
- Add messaging.normalizeTarget and targetResolver for user ID resolution
- Add directory stubs (self, listPeers, listGroups)
- Add agentPrompt.messageToolHints with Synology Chat formatting guide
- 63 tests (up from 54), all passing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

extensions/synology-chat/src/client.test.ts

@@ -0,0 +1,104 @@
+import { EventEmitter } from "node:events";
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Mock http and https modules before importing the client
+vi.mock("node:https", () => {
+  const mockRequest = vi.fn();
+  return { default: { request: mockRequest }, request: mockRequest };
+});
+
+vi.mock("node:http", () => {
+  const mockRequest = vi.fn();
+  return { default: { request: mockRequest }, request: mockRequest };
+});
+
+// Import after mocks are set up
+const { sendMessage, sendFileUrl } = await import("./client.js");
+const https = await import("node:https");
+
+function mockSuccessResponse() {
+  const httpsRequest = vi.mocked(https.request);
+  httpsRequest.mockImplementation((_url: any, _opts: any, callback: any) => {
+    const res = new EventEmitter() as any;
+    res.statusCode = 200;
+    process.nextTick(() => {
+      callback(res);
+      res.emit("data", Buffer.from('{"success":true}'));
+      res.emit("end");
+    });
+    const req = new EventEmitter() as any;
+    req.write = vi.fn();
+    req.end = vi.fn();
+    req.destroy = vi.fn();
+    return req;
+  });
+}
+
+function mockFailureResponse(statusCode = 500) {
+  const httpsRequest = vi.mocked(https.request);
+  httpsRequest.mockImplementation((_url: any, _opts: any, callback: any) => {
+    const res = new EventEmitter() as any;
+    res.statusCode = statusCode;
+    process.nextTick(() => {
+      callback(res);
+      res.emit("data", Buffer.from("error"));
+      res.emit("end");
+    });
+    const req = new EventEmitter() as any;
+    req.write = vi.fn();
+    req.end = vi.fn();
+    req.destroy = vi.fn();
+    return req;
+  });
+}
+
+describe("sendMessage", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns true on successful send", async () => {
+    mockSuccessResponse();
+    const result = await sendMessage("https://nas.example.com/incoming", "Hello");
+    expect(result).toBe(true);
+  });
+
+  it("returns false on server error after retries", async () => {
+    mockFailureResponse(500);
+    const result = await sendMessage("https://nas.example.com/incoming", "Hello");
+    expect(result).toBe(false);
+  });
+
+  it("includes user_ids when userId is numeric", async () => {
+    mockSuccessResponse();
+    await sendMessage("https://nas.example.com/incoming", "Hello", 42);
+    const httpsRequest = vi.mocked(https.request);
+    expect(httpsRequest).toHaveBeenCalled();
+    const callArgs = httpsRequest.mock.calls[0];
+    expect(callArgs[0]).toBe("https://nas.example.com/incoming");
+  });
+});
+
+describe("sendFileUrl", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("returns true on success", async () => {
+    mockSuccessResponse();
+    const result = await sendFileUrl(
+      "https://nas.example.com/incoming",
+      "https://example.com/file.png",
+    );
+    expect(result).toBe(true);
+  });
+
+  it("returns false on failure", async () => {
+    mockFailureResponse(500);
+    const result = await sendFileUrl(
+      "https://nas.example.com/incoming",
+      "https://example.com/file.png",
+    );
+    expect(result).toBe(false);
+  });
+});