docs: add AGENTS.md agent guide and absolute README links

AGENTS.md

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+# AGENTS.md — OneSignal Node (TypeScript) SDK
+
+Integration guide for AI agents and LLMs using `@onesignal/node-onesignal`, the OneSignal server SDK for Node.js. Human-oriented docs are in the [README](./README.md).
+
+## What this SDK does
+
+Server-side access to the OneSignal REST API: send push / email / SMS, manage users, subscriptions, segments, templates and live activities, and administer apps & API keys.
+
+- Package: `@onesignal/node-onesignal`
+- Repository: https://github.com/OneSignal/node-onesignal
+
+## Install
+
+```sh
+npm install @onesignal/node-onesignal
+```
+
+## Authentication — two key types
+
+OneSignal uses two bearer credentials; each endpoint requires a specific one:
+
+- **REST API key** — used by almost every endpoint (notifications, users, subscriptions, segments, templates, live activities, custom events). Found in **App Settings → Keys & IDs**.
+- **Organization API key** — required *only* for organization-level endpoints: app management (list / create / get / update apps), API-key management (view / create / update / rotate / delete API keys), and copying a template to another app. Found in **Organization Settings**.
+
+Set both on one configuration; the SDK sends the correct credential per endpoint. Never hard-code keys — read them from environment variables or a secrets manager.
+
+```javascript
+const OneSignal = require('@onesignal/node-onesignal');
+
+const configuration = OneSignal.createConfiguration({
+    restApiKey: process.env.ONESIGNAL_REST_API_KEY,
+    organizationApiKey: process.env.ONESIGNAL_ORGANIZATION_API_KEY,
+});
+
+const client = new OneSignal.DefaultApi(configuration);
+```
+
+## Calling convention
+
+Methods take **positional arguments**. Build the model object and pass it directly — do **not** wrap arguments in a request/options object.
+
+```javascript
+const notification = new OneSignal.Notification();
+notification.app_id = 'YOUR_APP_ID';
+notification.contents = { en: 'Hello from OneSignal!' };
+notification.include_aliases = { external_id: ['YOUR_USER_EXTERNAL_ID'] };
+notification.target_channel = 'push';
+
+const response = await client.createNotification(notification);
+```
+
+## Idempotent sends & retries
+
+Set `idempotency_key` (a UUID) so a create-notification request can be safely retried — the server returns the original result instead of sending twice. The `createNotificationWithRetry` helper handles this for you: it generates an `idempotency_key` when absent, retries `429` / `503` / transport errors with the **same** key (honoring `Retry-After`), and reports via `wasReplayed` whether the server answered from a previously completed request.
+
+```javascript
+const result = await client.createNotificationWithRetry(notification, { maxRetries: 5, baseDelayMs: 1000 });
+console.log('id:', result.response.id, 'replayed:', result.wasReplayed);
+```
+
+> The notification-level `external_id` field is the **deprecated** idempotency mechanism — prefer `idempotency_key`. Don't confuse it with the `external_id` **alias label** (under `include_aliases`) used to target users.
+
+## Full API reference
+
+- [DefaultApi.md](https://github.com/OneSignal/node-onesignal/blob/main/DefaultApi.md) — every endpoint, parameter, and model, with runnable examples.
+- [OneSignal REST API reference](https://documentation.onesignal.com/reference)

CLAUDE.md

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+# CLAUDE.md
+
+AI agent and LLM integration guidance for this OneSignal server SDK lives in **[AGENTS.md](./AGENTS.md)** — authentication, calling conventions, idempotent retries, and the full API reference.
+
+See [AGENTS.md](./AGENTS.md).

README.md

@@ -13,6 +13,8 @@
 
 The OneSignal Node client is a server SDK for NodeJS. A powerful way to send personalized messages at scale and build effective customer engagement strategies. Learn more at [onesignal.com](https://onesignal.com).
 
+> **Building with an AI agent or LLM?** See [AGENTS.md](https://github.com/OneSignal/node-onesignal/blob/main/AGENTS.md) for an agent-oriented integration guide — authentication, calling conventions, idempotent retries, and the full API reference.
+
 ## Installation
 
 ```sh