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

AGENTS.md

@@ -0,0 +1,66 @@
+# AGENTS.md — OneSignal Ruby SDK
+
+Integration guide for AI agents and LLMs using the `onesignal` gem, the OneSignal server SDK for Ruby. 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.
+
+- Gem: `onesignal`
+- Repository: https://github.com/OneSignal/onesignal-ruby-api
+
+## Install
+
+```sh
+gem install 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**.
+
+Configure both; the SDK sends the correct credential per endpoint. Never hard-code keys — read them from environment variables or a secrets manager.
+
+```ruby
+require 'onesignal'
+
+OneSignal.configure do |config|
+  config.rest_api_key = ENV['ONESIGNAL_REST_API_KEY']
+  config.organization_api_key = ENV['ONESIGNAL_ORGANIZATION_API_KEY']
+end
+
+client = OneSignal::DefaultApi.new
+```
+
+## Calling convention
+
+Methods take **positional arguments**. Build the model object and pass it directly — do **not** wrap arguments in a request/options object.
+
+```ruby
+notification = OneSignal::Notification.new
+notification.app_id = 'YOUR_APP_ID'
+notification.contents = OneSignal::LanguageStringMap.new({ en: 'Hello from OneSignal!' })
+notification.include_aliases = { 'external_id' => ['YOUR_USER_EXTERNAL_ID'] }
+notification.target_channel = 'push'
+
+response = client.create_notification(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 `create_notification_with_retry` 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 `was_replayed` whether the server answered from a previously completed request.
+
+```ruby
+result = client.create_notification_with_retry(notification, max_retries: 5, base_delay: 1.0)
+puts "id: #{result.response.id}, replayed: #{result.was_replayed}"
+```
+
+> 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/onesignal-ruby-api/blob/master/docs/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

@@ -2,6 +2,8 @@
 
 OneSignal - the Ruby gem for OneSignal
 
+> **Building with an AI agent or LLM?** See [AGENTS.md](https://github.com/OneSignal/onesignal-ruby-api/blob/master/AGENTS.md) for an agent-oriented integration guide — authentication, calling conventions, idempotent retries, and the full API reference.
+
 A powerful way to send personalized messages at scale and build effective customer engagement strategies. Learn more at onesignal.com
 
 - API version: 5.8.0