feat(timetable): 60s Redis idempotency-key middleware

RFC v0.2 R1 — Idempotency-Key replay window for POST
/api/v1/events/{event}/timetable/move. Narrow scope by design: the
12-hour ARCH §10 default would let a cached cascade-bump response
overwrite a fresh edit; 60 seconds covers honest network retry but
expires before a meaningful conflict can emerge.

Backed by the Laravel Cache facade (Redis in non-test env). Cache key
namespace `idempotency:60s:*` distinct from FormSubmission's
DB-column idempotency. Replays carry an `Idempotency-Replayed: true`
header so observability can distinguish them.

Registered as the route-middleware alias `idempotency.60s` in
bootstrap/app.php; will be applied on the move route in Step 8.

Missing or empty Idempotency-Key returns 400 with
`{"error":"idempotency_key_required"}`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/app/Http/Middleware/IdempotencyKey60sRedis.php

@@ -0,0 +1,76 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Cache;
+use Symfony\Component\HttpFoundation\Response;
+
+/**
+ * RFC v0.2 R1 — 60-second Idempotency-Key replay window backed by
+ * Redis cache.
+ *
+ * Why 60s and not the 12-hour MySQL window from ARCH §10:
+ * a stale 12-hour replay of the cascade-bump endpoint can corrupt
+ * timetable state in hard-to-detect ways (the persisted lanes have
+ * since been edited; replaying a cached response over a fresh edit
+ * would silently undo it). 60 seconds covers honest network retry
+ * without giving stale requests a window in which to resurrect.
+ *
+ * Storage: Laravel Cache facade with the default store (Redis in
+ * non-test environments). The key namespace `idempotency:60s:` is
+ * deliberately distinct from any other idempotency surface in the
+ * codebase — keys never collide with the FormSubmission DB-column
+ * idempotency.
+ *
+ * Applied today only on `POST /api/v1/events/{event}/timetable/move`.
+ * Other R-numbered idempotent endpoints (RFC §6 lists POST
+ * /performances and POST /engagements as candidates) get the regular
+ * 12-hour pattern when ARCH §10 lands; this middleware is purposely
+ * narrow.
+ */
+final class IdempotencyKey60sRedis
+{
+    public function handle(Request $request, Closure $next): Response
+    {
+        $key = $request->header('Idempotency-Key');
+
+        if (! is_string($key) || trim($key) === '') {
+            return response()->json(
+                ['error' => 'idempotency_key_required'],
+                400,
+            );
+        }
+
+        $cacheKey = 'idempotency:60s:'.$key;
+        $cached = Cache::get($cacheKey);
+
+        if (is_array($cached)) {
+            $response = response($cached['body'], $cached['status']);
+            foreach ($cached['headers'] ?? [] as $name => $value) {
+                $response->headers->set($name, $value);
+            }
+            $response->headers->set('Idempotency-Replayed', 'true');
+
+            return $response;
+        }
+
+        /** @var Response $response */
+        $response = $next($request);
+
+        if ($response->isSuccessful()) {
+            Cache::put($cacheKey, [
+                'status' => $response->getStatusCode(),
+                'body' => $response->getContent(),
+                'headers' => [
+                    'Content-Type' => $response->headers->get('Content-Type'),
+                ],
+            ], 60);
+        }
+
+        return $response;
+    }
+}

api/bootstrap/app.php

@@ -59,6 +59,9 @@ return Application::configure(basePath: dirname(__DIR__))
             'portal.token' => \App\Http\Middleware\PortalTokenMiddleware::class,
             'role' => \Spatie\Permission\Middleware\RoleMiddleware::class,
             'impersonation' => \App\Http\Middleware\HandleImpersonation::class,
+            // RFC-TIMETABLE v0.2 R1 — 60s Redis idempotency window for
+            // POST /timetable/move. Narrow scope by design.
+            'idempotency.60s' => \App\Http\Middleware\IdempotencyKey60sRedis::class,
         ]);
     })
     ->withExceptions(function (Exceptions $exceptions): void {