App subscriptions: manage a user's subscriptions with the app's own token

- $user->appSubscriptions(): create (idempotency_key), find, all, checkout, revoke, pause,
  resume, update against /v1/client/subscriptions with a client credentials token, so apps don't
  depend on the user's login
- user id from the billable's anikeen_id (AnikeenId::useUserIdField())
- ApiException with status, stable error code, isNotFound/isConflict/isTemporary; network
  errors no longer escape as raw Guzzle exceptions
- rejected app tokens are renewed once; asApp() never changes the shared client's token
- tests (testbench + Guzzle mock) and CI

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/Id/Resources/AppSubscriptions.php

@@ -0,0 +1,116 @@
+<?php
+
+namespace Anikeen\Id\Resources;
+
+use Anikeen\Id\AnikeenId;
+use Anikeen\Id\Contracts\Billable;
+use Anikeen\Id\Exceptions\ApiException;
+use Anikeen\Id\Support\AppRequest;
+use Illuminate\Database\Eloquent\Model;
+use InvalidArgumentException;
+
+/**
+ * Subscriptions of a user, managed with the app's own token (client credentials, scope
+ * `subscriptions:client`) instead of the user's token, so they keep working when the user's
+ * login expired. The app has to be trusted by the ID service. Nothing is requested until a
+ * method is called.
+ */
+class AppSubscriptions
+{
+    public function __construct(protected Billable|Model $billable)
+    {
+    }
+
+    /**
+     * The user's Anikeen ID (see AnikeenId::useUserIdField()).
+     */
+    public function userId(): string
+    {
+        $userId = $this->billable->{AnikeenId::getUserIdField()} ?? null;
+
+        if (empty($userId)) {
+            throw new InvalidArgumentException(sprintf('The billable has no Anikeen ID in [%s].', AnikeenId::getUserIdField()));
+        }
+
+        return (string) $userId;
+    }
+
+    /**
+     * Create a subscription for the user (it is billed only after checkout()).
+     *
+     * @param array{
+     *     group?: null|string,
+     *     name: string,
+     *     description?: null|string,
+     *     unit: string,
+     *     price: float|string,
+     *     vat_rate?: float,
+     *     payload?: null|array,
+     *     ends_at?: null|string,
+     *     webhook_url?: null|string,
+     *     webhook_secret?: null|string,
+     *     idempotency_key?: null|string
+     * } $attributes With an idempotency_key (max. 191 characters), a retried call returns the
+     *               subscription created by the first one instead of a duplicate.
+     *
+     * @throws ApiException
+     */
+    public function create(array $attributes): AppSubscription
+    {
+        return new AppSubscription(AppRequest::send('POST', 'v1/client/subscriptions', [
+            ...$attributes,
+            'user_id' => $this->userId(),
+        ])->data);
+    }
+
+    /**
+     * Find one of the user's subscriptions; null when it doesn't exist (or belongs to someone else).
+     *
+     * @throws ApiException
+     */
+    public function find(string $id): ?AppSubscription
+    {
+        try {
+            $subscription = new AppSubscription(AppRequest::send('GET', sprintf('v1/client/subscriptions/%s', $id))->data);
+        } catch (ApiException $e) {
+            if ($e->isNotFound()) {
+                return null;
+            }
+
+            throw $e;
+        }
+
+        return $subscription->user_id === $this->userId() ? $subscription : null;
+    }
+
+    /**
+     * All of the user's subscriptions, optionally filtered.
+     *
+     * @param array{group?: string, active?: bool, cancelled?: bool} $filters
+     * @return list<AppSubscription>
+     *
+     * @throws ApiException
+     */
+    public function all(array $filters = []): array
+    {
+        $subscriptions = [];
+        $page = 1;
+
+        do {
+            $result = AppRequest::send('GET', 'v1/client/subscriptions', null, [
+                ...array_map(fn ($value) => is_bool($value) ? (int) $value : $value, $filters),
+                'user_id' => $this->userId(),
+                'per_page' => 100,
+                'page' => $page,
+            ]);
+
+            foreach ($result->data as $data) {
+                $subscriptions[] = new AppSubscription($data);
+            }
+
+            $lastPage = (int) ($result->meta->last_page ?? $page);
+        } while ($page++ < $lastPage);
+
+        return $subscriptions;
+    }
+}