feat(form-builder): per-schema default_crowd_type_id replaces silent oldest() heuristic (WS-6)

Session 2's PersonProvisioner picked CrowdType::oldest() for the org —
silently wrong for multi-crowd_type orgs (Volunteer + Crew + Press are
three distinct crowd_types in one org). Schemas now declare their
target crowd_type explicitly via form_schemas.default_crowd_type_id.
RequiresDefaultCrowdType publish guard prevents misconfigured
event_registration schemas from publishing.

PersonProvisioner: oldest() fallback removed entirely. Misconfiguration
throws no_default_crowd_type at runtime; publish guard prevents it at
config time.

Migration uses a plain ulid() column without DB-level FK because
SQLite's table-rebuild on ALTER ADD FOREIGN KEY cascade-deletes
form_fields rows (form_fields.form_schema_id has cascadeOnDelete on
form_schemas). Application-level integrity via FormSchema::defaultCrowdType()
belongsTo + the publish guard + the runtime failsafe — three load-bearing
checks, none of which require the DB-level constraint.

Three pre-existing migration backfill tests bumped step counts +1 to
account for the new migration sitting between WS-5c and WS-5d:
FormFieldBindingMigrationTest (16→17, 14→15), FormFieldConfigBackfillAndDropTest
(11→12), FormFieldValidationRuleBackfillTest (14→15),
ConditionalLogicBackfillTest (5→6).

Six event_registration test fixtures updated to set default_crowd_type_id
to satisfy the new publish guard.

FormBuilderDevSeeder.resolveDefaultCrowdTypeId() — VOLUNTEER → first-active
→ create-as-needed fallback chain; documented contract for future seeders.

SCHEMA.md updated to v2.7.
Refs: RFC-WS-6.md v1.1 §3 Q8 addendum (Task 4 of this session)

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

api/database/migrations/2026_04_26_120000_add_default_crowd_type_id_to_form_schemas.php

@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+/**
+ * RFC-WS-6 v1.1 §3 Q8 addendum — per-schema default CrowdType for
+ * Person provisioning. Replaces the silent oldest() heuristic from
+ * WS-6 session 2 with explicit configuration; RequiresDefaultCrowdType
+ * publish guard ensures event_registration schemas declare it.
+ *
+ * No backfill: pre-launch the table is empty. Dev seeders populate
+ * the column when reseeding (FormBuilderDevSeeder).
+ */
+return new class extends Migration
+{
+    public function up(): void
+    {
+        // Plain nullable ULID column. NO database-level foreign key —
+        // SQLite's rebuild-on-FK-add cascade-deletes form_fields rows
+        // (form_fields.form_schema_id has cascadeOnDelete on
+        // form_schemas), which corrupts running migration tests.
+        // Application-level integrity: FormSchema::defaultCrowdType()
+        // belongsTo loads from CrowdType; CrowdTypeObserver could add
+        // a soft-handle on delete if needed in production. The new
+        // RequiresDefaultCrowdType publish guard plus the runtime
+        // failsafe in PersonProvisioner are the load-bearing checks.
+        Schema::table('form_schemas', function (Blueprint $table): void {
+            $table->ulid('default_crowd_type_id')
+                ->nullable()
+                ->after('purpose');
+
+            $table->index(['organisation_id', 'default_crowd_type_id'], 'fs_org_default_crowd_type_idx');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('form_schemas', function (Blueprint $table): void {
+            $table->dropIndex('fs_org_default_crowd_type_idx');
+            $table->dropColumn('default_crowd_type_id');
+        });
+    }
+};

api/database/seeders/FormBuilderDevSeeder.php

@@ -10,6 +10,7 @@ use App\Enums\FormBuilder\FormSchemaSnapshotMode;
 use App\Enums\FormBuilder\FormSubmissionMode;
 use App\Enums\FormBuilder\FormSubmissionStatus;
 use App\Enums\FormBuilder\FormValueStorageHint;
+use App\Models\CrowdType;
 use App\Models\Event;
 use App\Models\FormBuilder\FormField;
 use App\Models\FormBuilder\FormSchema;
@@ -132,6 +133,7 @@ final class FormBuilderDevSeeder
             'name' => $event->name.' — registratie',
             'slug' => Str::slug($event->slug.'-registratie'),
             'purpose' => FormPurpose::EVENT_REGISTRATION,
+            'default_crowd_type_id' => self::resolveDefaultCrowdTypeId((string) $event->organisation_id),
             'description' => "Registratieformulier voor {$event->name}.",
             'is_published' => in_array(
                 $event->status,
@@ -391,6 +393,7 @@ final class FormBuilderDevSeeder
             'name' => $name,
             'slug' => $slug,
             'purpose' => FormPurpose::EVENT_REGISTRATION,
+            'default_crowd_type_id' => self::resolveDefaultCrowdTypeId((string) $org->id),
             'description' => "Demo-formulier voor het end-to-end doorlopen van de vrijwilligersregistratie voor {$event->name}.",
             'is_published' => true,
             'submission_mode' => FormSubmissionMode::DRAFT_SINGLE,
@@ -615,6 +618,46 @@ final class FormBuilderDevSeeder
             ->count();
     }
 
+    /**
+     * RFC-WS-6 v1.1 §3 Q8 addendum — event_registration schemas declare
+     * a target CrowdType. DevSeeder picks the VOLUNTEER system_type
+     * (DevSeeder::run() always seeds it for every dev org); falls back
+     * to the first active CrowdType if VOLUNTEER is somehow missing,
+     * and creates a minimal CrowdType row as last-resort to satisfy the
+     * NOT NULL FK on Person.crowd_type_id.
+     *
+     * Future seeders MUST keep this lookup contract: schemas need a
+     * resolvable CrowdType per org or the RequiresDefaultCrowdType
+     * publish guard will block publish.
+     */
+    private static function resolveDefaultCrowdTypeId(string $organisationId): string
+    {
+        $crowdType = CrowdType::query()
+            ->withoutGlobalScopes()
+            ->where('organisation_id', $organisationId)
+            ->where('is_active', true)
+            ->where('system_type', 'VOLUNTEER')
+            ->first()
+            ?? CrowdType::query()
+                ->withoutGlobalScopes()
+                ->where('organisation_id', $organisationId)
+                ->where('is_active', true)
+                ->oldest()
+                ->first();
+
+        if ($crowdType === null) {
+            $crowdType = CrowdType::create([
+                'organisation_id' => $organisationId,
+                'name' => 'Vrijwilliger',
+                'system_type' => 'VOLUNTEER',
+                'color' => '#10b981',
+                'is_active' => true,
+            ]);
+        }
+
+        return (string) $crowdType->id;
+    }
+
     private static function uniqueSchemaSlug(Organisation $org, string $base): string
     {
         $candidate = $base;