Add WordPress Abilities API integration

.github/changelog/add-abilities-api

@@ -0,0 +1,4 @@
+Significance: minor
+Type: added
+
+Add a WordPress Abilities API integration (WordPress 6.9+) so other plugins can discover and use ActivityPub features such as resolving handles, fetching actors, and managing followers through a stable API.

activitypub.php

@@ -124,6 +124,10 @@ function plugin_init() {
 		\add_action( 'init', array( __NAMESPACE__ . '\Relay', 'init' ) );
 	}
 
+	// WordPress Abilities API (WP 6.9+). These hooks only fire when the API is available.
+	\add_action( 'wp_abilities_api_categories_init', array( __NAMESPACE__ . '\Abilities', 'register_categories' ) );
+	\add_action( 'wp_abilities_api_init', array( __NAMESPACE__ . '\Abilities', 'register_abilities' ) );
+
 	// Load development tools.
 	if ( 'local' === wp_get_environment_type() ) {
 		$loader_file = __DIR__ . '/local/load.php';

docs/abilities-api.md

@@ -0,0 +1,262 @@
+# ActivityPub Abilities API
+
+The ActivityPub plugin exposes its functionality through the [WordPress Abilities API](https://make.wordpress.org/core/) (WordPress 6.9+). Abilities are discoverable, schema-validated, permissioned operations that other plugins, automation tools, WP-CLI, and the REST API can call by name — without depending on the plugin's internal classes.
+
+## Contents
+
+- [Why use abilities](#why-use-abilities)
+- [Quick start](#quick-start)
+- [Authorization](#authorization)
+- [Categories](#categories)
+- [Ability reference](#ability-reference)
+  - [Discovery](#discovery)
+  - [Social](#social)
+- [REST API access](#rest-api-access)
+- [Architecture](#architecture)
+- [Extending the API](#extending-the-api)
+- [Roadmap](#roadmap)
+
+## Why use abilities
+
+- **Stable contract.** Call `activitypub/get-followers` by name; the plugin can refactor `Collection\Followers` freely without breaking you.
+- **Discoverable.** Abilities advertise their input/output JSON Schema, category, and annotations, so tooling can introspect them.
+- **Permissioned.** Every ability runs through a permission callback before executing.
+- **Multiple surfaces.** The same ability is reachable from PHP (`wp_run_ability()`), the REST API (`/wp-json/wp-abilities/v1/`), and any future Abilities-aware client.
+
+## Quick start
+
+Check availability before calling — the API only exists on WordPress 6.9+ and when the plugin is active:
+
+```php
+if ( function_exists( 'wp_get_ability' ) && wp_get_ability( 'activitypub/get-followers' ) ) {
+	// The ability is registered and can be run.
+}
+```
+
+Run an ability and handle the `WP_Error` result:
+
+```php
+$result = wp_run_ability(
+	'activitypub/get-followers',
+	array(
+		'user_id'  => get_current_user_id(),
+		'per_page' => 20,
+		'page'     => 1,
+	)
+);
+
+if ( ! is_wp_error( $result ) ) {
+	foreach ( $result['followers'] as $follower ) {
+		printf( "%s (%s)\n", $follower['name'], $follower['preferredUsername'] );
+	}
+	printf( "Total: %d\n", $result['total'] );
+}
+```
+
+## Authorization
+
+Every ability requires the current user to have the `activitypub` capability (`current_user_can( 'activitypub' )`). Some abilities apply additional rules:
+
+| Rule | Applies to | Behavior |
+|------|-----------|----------|
+| **Ownership** | `get-followers`, `get-following`, `follow`, `unfollow` | Acting on another user's data requires `manage_options`, otherwise returns `403 activitypub_forbidden`. `user_id` defaults to the current user. |
+| **Feature flag** | `follow`, `unfollow` | Requires the Following UI to be enabled (`activitypub_following_ui` option). Otherwise returns `403 activitypub_following_disabled`. |
+
+Each ability also declares behavioral annotations (`readonly`, `destructive`, `idempotent`) so clients can reason about side effects before running them.
+
+## Categories
+
+| Slug | Label | Description |
+|------|-------|-------------|
+| `activitypub-discovery` | Discovery | Look up and discover remote actors in the Fediverse. |
+| `activitypub-social` | Social | Manage followers, following, and social connections. |
+
+## Ability reference
+
+Every input is an object; `additionalProperties` is disallowed. All abilities return either the documented array or a `WP_Error`.
+
+### Discovery
+
+#### `activitypub/resolve-handle`
+
+Resolve a WebFinger handle to its ActivityPub data. *Readonly · idempotent.*
+
+| Input | Type | Required | Notes |
+|-------|------|----------|-------|
+| `handle` | string | yes | WebFinger handle, e.g. `user@example.com`. |
+
+**Returns:** the WebFinger document (object). **Errors:** `WP_Error` if the handle cannot be resolved.
+
+```php
+$data = wp_run_ability( 'activitypub/resolve-handle', array( 'handle' => 'alice@example.com' ) );
+```
+
+#### `activitypub/get-actor`
+
+Fetch profile information for a remote actor. *Readonly · idempotent.*
+
+| Input | Type | Required | Notes |
+|-------|------|----------|-------|
+| `actor` | string | yes | Actor URL or WebFinger handle. |
+
+**Returns:**
+
+```jsonc
+{
+  "id": "https://example.com/users/alice",   // uri
+  "type": "Person",
+  "name": "Alice",
+  "preferredUsername": "alice",
+  "summary": "…",
+  "inbox": "https://example.com/users/alice/inbox",
+  "outbox": "https://example.com/users/alice/outbox",
+  "followers": "https://example.com/users/alice/followers",
+  "following": "https://example.com/users/alice/following",
+  "icon": { /* … */ }
+}
+```
+
+**Errors:** `WP_Error` if the actor cannot be fetched or parsed.
+
+### Social
+
+#### `activitypub/get-followers`
+
+List followers for a local actor. *Readonly · idempotent.*
+
+| Input | Type | Required | Default | Notes |
+|-------|------|----------|---------|-------|
+| `user_id` | integer | yes | — | The local actor's user ID. |
+| `page` | integer | no | `1` | Page number. |
+| `per_page` | integer | no | `20` | Results per page (capped at `100`). |
+
+**Returns:** `{ "followers": Actor[], "total": integer }`, where each follower has `id`, `type`, `name`, `preferredUsername`, `followers`, `following`, `icon`. **Errors:** `400 activitypub_invalid_user_id`, `403 activitypub_forbidden` (another user's list without `manage_options`).
+
+#### `activitypub/get-following`
+
+List accounts a local actor follows. *Readonly · idempotent.*
+
+| Input | Type | Required | Default | Notes |
+|-------|------|----------|---------|-------|
+| `user_id` | integer | yes | — | The local actor's user ID. |
+| `page` | integer | no | `1` | Page number. |
+| `per_page` | integer | no | `20` | Results per page (capped at `100`). |
+
+**Returns:** `{ "following": Actor[], "total": integer }` (same `Actor` shape as above). **Errors:** `400 activitypub_invalid_user_id`, `403 activitypub_forbidden` (another user's list without `manage_options`).
+
+#### `activitypub/follow`
+
+Follow a remote actor. *Not readonly · not idempotent.* Requires the Following feature to be enabled.
+
+| Input | Type | Required | Default | Notes |
+|-------|------|----------|---------|-------|
+| `actor` | string | yes | — | Actor URL or WebFinger handle to follow. |
+| `user_id` | integer | no | current user | Local actor to act as (ownership rules apply). |
+
+**Returns:** `{ "outbox_item_id": integer, "status": "pending" }`. **Errors:** `403 activitypub_following_disabled`, `403 activitypub_forbidden`, or a `WP_Error` from the follow request.
+
+```php
+$result = wp_run_ability( 'activitypub/follow', array( 'actor' => 'organizer@events.example.com' ) );
+```
+
+#### `activitypub/unfollow`
+
+Unfollow a remote actor. *Not readonly · not idempotent.* Requires the Following feature to be enabled.
+
+| Input | Type | Required | Default | Notes |
+|-------|------|----------|---------|-------|
+| `actor` | string | yes | — | Actor URL or WebFinger handle to unfollow. |
+| `user_id` | integer | no | current user | Local actor to act as (ownership rules apply). |
+
+**Returns:** `{ "success": true }`. **Errors:** `403 activitypub_following_disabled`, `403 activitypub_forbidden`, or a `WP_Error` from the unfollow request.
+
+## REST API access
+
+Abilities with `show_in_rest` are reachable under `/wp-json/wp-abilities/v1/`. Readonly abilities run via `GET`; others via `POST`.
+
+```bash
+# List categories.
+curl -u admin:PASSWORD http://localhost:8888/wp-json/wp-abilities/v1/categories
+
+# List Discovery abilities.
+curl -u admin:PASSWORD 'http://localhost:8888/wp-json/wp-abilities/v1/abilities?category=activitypub-discovery'
+
+# Run a readonly ability (GET).
+curl -u admin:PASSWORD 'http://localhost:8888/wp-json/wp-abilities/v1/abilities/activitypub/get-actor/run?input[actor]=alice@example.com'
+
+# Run a write ability (POST).
+curl -u admin:PASSWORD -X POST -H 'Content-Type: application/json' \
+  -d '{"input":{"actor":"alice@example.com"}}' \
+  http://localhost:8888/wp-json/wp-abilities/v1/abilities/activitypub/follow/run
+```
+
+## Architecture
+
+```
+activitypub.php                      # Hooks Abilities::register_* into wp_abilities_api_*_init
+includes/
+├── class-abilities.php              # Category registration, orchestration, extensibility hooks
+└── ability/
+    ├── class-actor.php              # activitypub/get-actor
+    ├── class-followers.php          # activitypub/get-followers
+    ├── class-following.php          # activitypub/get-following, follow, unfollow
+    └── class-webfinger.php          # activitypub/resolve-handle
+```
+
+Registration flow:
+
+1. `activitypub.php` hooks `Abilities::register_categories()` into `wp_abilities_api_categories_init` and `Abilities::register_abilities()` into `wp_abilities_api_init`. These hooks only fire when the Abilities API is available, so no version check is needed.
+2. `register_categories()` registers the categories, then fires `activitypub_register_ability_categories`.
+3. `register_abilities()` calls each ability class's `register()`, then fires `activitypub_register_abilities`.
+
+Ability classes are grouped by domain (`Webfinger`, `Actor`, `Followers`, `Following`), not one class per ability — a single class can register several abilities, even across categories.
+
+## Extending the API
+
+Third-party plugins register their own categories and abilities on the same hooks:
+
+```php
+add_action( 'activitypub_register_ability_categories', function () {
+	wp_register_ability_category( 'my-plugin', array(
+		'label'       => __( 'My Plugin', 'my-plugin' ),
+		'description' => __( 'Custom abilities.', 'my-plugin' ),
+	) );
+} );
+
+add_action( 'activitypub_register_abilities', function () {
+	wp_register_ability( 'my-plugin/do-thing', array(
+		'label'               => __( 'Do Thing', 'my-plugin' ),
+		'description'         => __( 'Does the thing.', 'my-plugin' ),
+		'category'            => 'my-plugin',
+		'execute_callback'    => 'my_plugin_do_thing',
+		'permission_callback' => '__return_true',
+		'input_schema'        => array(
+			'type'                 => 'object',
+			'properties'           => array(
+				'param' => array( 'type' => 'string' ),
+			),
+			'required'             => array( 'param' ),
+			'additionalProperties' => false,
+		),
+		'output_schema'       => array( 'type' => 'object' ),
+		'meta'                => array(
+			'annotations'  => array( 'readonly' => true, 'destructive' => false, 'idempotent' => true ),
+			'show_in_rest' => true,
+		),
+	) );
+} );
+```
+
+## Roadmap
+
+Abilities under consideration for future releases:
+
+| Ability | Category | Description |
+|---------|----------|-------------|
+| `activitypub/publish-note` | Publish | Publish a Note to the Fediverse. |
+| `activitypub/announce-post` | Publish | Boost/announce an existing post. |
+| `activitypub/block-actor` | Moderation | Block a specific actor. |
+| `activitypub/block-domain` | Moderation | Block an entire domain. |
+| `activitypub/unblock` | Moderation | Unblock an actor or domain. |
+| `activitypub/get-inbox` | Moderation | Get recent inbox activities. |
+| `activitypub/retry-delivery` | Moderation | Retry failed activity delivery. |

docs/developer-docs.md

@@ -4,6 +4,7 @@
 - [Introduction](#introduction)
 - [Snippets](#snippets)
 - [Extending the Settings Interface](#extending-the-settings-interface)
+- [Abilities API](#abilities-api)
 
 ## Introduction
 This documentation provides information for developers who want to extend and build upon the ActivityPub plugin. Whether you're developing a complementary plugin or integrating ActivityPub features into your existing WordPress plugin, this guide will help you understand the available hooks and customization options.
@@ -77,3 +78,9 @@ add_action( 'admin_enqueue_scripts', function( $hook ) {
     }
 } );
 ```
+
+## Abilities API
+
+The plugin registers its operations as WordPress Abilities (WP 6.9+), giving other plugins a stable, discoverable way to interact with ActivityPub without depending on internal classes.
+
+See [Abilities API](./abilities-api.md) for the available abilities, their input and output schemas, and usage examples.