feat(timetable): four custom validation rules for artist domain

StageActiveOnEvent — checks the candidate stage_id is linked to the
given event_id via stage_days. Covers performance create/update
(perf.event_id ↔ stage) and the timetable move endpoint
(target_stage_id ↔ resolved target event).

WithinEventBounds — checks a candidate datetime is inside the event's
[start_at, end_at] window. Used for performance start/end dates and
move-target dates against the relevant sub-event for festivals.

OptionExpiresInFuture — conditional rule fired only when
booking_status === 'option'. Asserts option_expires_at is set and in
the future. Implementation of RFC §10.1 transition gate at the
request layer (the service layer enforces the same invariant).

ContractRequiresFee — conditional rule fired only when
booking_status === 'contracted'. Asserts fee_amount is set and > 0.
Same dual-layer enforcement as OptionExpiresInFuture.

All four pass silently when the validated field is null or the
context is irrelevant — the FormRequest still owns the surrounding
required/nullable/exists rules.

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

api/app/Rules/Artist/ContractRequiresFee.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Rules\Artist;
+
+use App\Enums\Artist\ArtistEngagementStatus;
+use Closure;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+/**
+ * Conditional rule: when `booking_status === 'contracted'`, the
+ * `fee_amount` field must be set and greater than zero.
+ *
+ * Bound from the engagement FormRequest, taking the inbound
+ * booking_status value at construction time.
+ */
+final class ContractRequiresFee implements ValidationRule
+{
+    public function __construct(
+        private readonly ?string $bookingStatus,
+    ) {}
+
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        if ($this->bookingStatus !== ArtistEngagementStatus::Contracted->value) {
+            return;
+        }
+
+        if ($value === null || $value === '') {
+            $fail('Bij status "Gecontracteerd" is een fee verplicht.');
+
+            return;
+        }
+
+        if ((float) $value <= 0) {
+            $fail('De fee moet groter dan 0 zijn.');
+        }
+    }
+}

api/app/Rules/Artist/OptionExpiresInFuture.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Rules\Artist;
+
+use App\Enums\Artist\ArtistEngagementStatus;
+use Carbon\CarbonImmutable;
+use Closure;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+/**
+ * Conditional rule: when `booking_status === 'option'`, the
+ * `option_expires_at` field must be set and in the future.
+ *
+ * Bound from the engagement FormRequest, taking the inbound
+ * booking_status value at construction time.
+ */
+final class OptionExpiresInFuture implements ValidationRule
+{
+    public function __construct(
+        private readonly ?string $bookingStatus,
+    ) {}
+
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        if ($this->bookingStatus !== ArtistEngagementStatus::Option->value) {
+            return;
+        }
+
+        if ($value === null || $value === '') {
+            $fail('Bij status "Optie" is een vervaldatum verplicht.');
+
+            return;
+        }
+
+        $candidate = CarbonImmutable::parse((string) $value);
+        if ($candidate->isPast()) {
+            $fail('De optie-vervaldatum moet in de toekomst liggen.');
+        }
+    }
+}

api/app/Rules/Artist/StageActiveOnEvent.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Rules\Artist;
+
+use App\Models\StageDay;
+use Closure;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+/**
+ * Validates that a candidate `stage_id` is linked to the given
+ * `event_id` via the `stage_days` pivot. Used by both
+ * CreatePerformanceRequest / UpdatePerformanceRequest (the perf's
+ * event_id sub-event must be active on the chosen stage) and
+ * MoveTimetablePerformanceRequest (target stage must be active on the
+ * resolved target event).
+ *
+ * Rule passes silently when value is null (the FormRequest still
+ * owns the `nullable` decision).
+ */
+final class StageActiveOnEvent implements ValidationRule
+{
+    public function __construct(
+        private readonly ?string $eventId,
+    ) {}
+
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        if ($value === null || $this->eventId === null) {
+            return;
+        }
+
+        $exists = StageDay::query()
+            ->where('stage_id', (string) $value)
+            ->where('event_id', $this->eventId)
+            ->exists();
+
+        if (! $exists) {
+            $fail('De gekozen stage is niet actief op deze (sub-)event.');
+        }
+    }
+}

api/app/Rules/Artist/WithinEventBounds.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Rules\Artist;
+
+use App\Models\Event;
+use Carbon\CarbonImmutable;
+use Closure;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+/**
+ * Validates that a candidate datetime sits inside the event's
+ * [start_at, end_at] window. Works for flat events (single window)
+ * and for sub-events (sub-event window); festival-level events are
+ * usually not the target — the FormRequest passes the *sub-event* id
+ * for performances and the *containing* event for the stage's day.
+ *
+ * Rule passes silently when value is null or when the event cannot
+ * be found (the FormRequest owns the `required`/`exists` decision).
+ */
+final class WithinEventBounds implements ValidationRule
+{
+    public function __construct(
+        private readonly ?string $eventId,
+    ) {}
+
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        if ($value === null || $this->eventId === null) {
+            return;
+        }
+
+        $event = Event::withoutGlobalScopes()->find($this->eventId);
+        if ($event === null) {
+            return;
+        }
+
+        $candidate = CarbonImmutable::parse((string) $value);
+        $start = CarbonImmutable::instance($event->start_at);
+        $end = CarbonImmutable::instance($event->end_at);
+
+        if ($candidate->lt($start) || $candidate->gt($end)) {
+            $fail(sprintf(
+                'De datum moet binnen het evenement (%s — %s) vallen.',
+                $start->format('Y-m-d H:i'),
+                $end->format('Y-m-d H:i'),
+            ));
+        }
+    }
+}