diff --git a/api/app/Services/FormBuilder/FormSubmissionService.php b/api/app/Services/FormBuilder/FormSubmissionService.php
index a56d6645..f0198b50 100644
--- a/api/app/Services/FormBuilder/FormSubmissionService.php
+++ b/api/app/Services/FormBuilder/FormSubmissionService.php
@@ -109,7 +109,9 @@ final class FormSubmissionService
             }
 
             if ($submission->opened_at !== null) {
-                $submission->submission_duration_seconds = now()->diffInSeconds($submission->opened_at);
+                // abs + int cast: Carbon's diffInSeconds returns signed fractional
+                // seconds, and the column is unsignedInteger.
+                $submission->submission_duration_seconds = (int) abs(now()->diffInSeconds($submission->opened_at));
             }
 
             $submission->save();
diff --git a/api/database/seeders/DevSeeder.php b/api/database/seeders/DevSeeder.php
index a07dc1db..8bda293a 100644
--- a/api/database/seeders/DevSeeder.php
+++ b/api/database/seeders/DevSeeder.php
@@ -926,6 +926,13 @@ class DevSeeder extends Seeder
             $submissions = FormBuilderDevSeeder::seedSubmissionsForEvent($festival, $formSchema);
             $this->command->info("  Form schema + 16 fields + {$submissions} submissions created");
 
+            // Sprint 0.5 showcase: public-token-enabled event_registration
+            // schema + draft + submitted submission that exercises
+            // FORM-02 / §31.10 TAG_PICKER sync end-to-end.
+            if (app()->environment('local', 'testing', 'development')) {
+                FormBuilderDevSeeder::seedEventRegistrationShowcase($this->org, $festival, $this->command);
+            }
+
             $this->command->info('  Echt Feesten 2026 complete');
         });
     }
diff --git a/api/database/seeders/FormBuilderDevSeeder.php b/api/database/seeders/FormBuilderDevSeeder.php
index b25393ed..14f9c683 100644
--- a/api/database/seeders/FormBuilderDevSeeder.php
+++ b/api/database/seeders/FormBuilderDevSeeder.php
@@ -18,6 +18,11 @@ use App\Models\FormBuilder\FormTemplate;
 use App\Models\FormBuilder\FormValue;
 use App\Models\Organisation;
 use App\Models\Person;
+use App\Models\PersonTag;
+use App\Models\UserOrganisationTag;
+use App\Services\FormBuilder\FormSubmissionService;
+use App\Services\FormBuilder\FormValueService;
+use Illuminate\Console\Command;
 use Illuminate\Support\Str;
 
 /**
@@ -227,4 +232,317 @@ final class FormBuilderDevSeeder
             'value' => $value,
         ]);
     }
+
+    // =========================================================================
+    // Sprint 0.5 — event_registration showcase (FORM-02 / §31.10 demo)
+    //
+    // Creates ONE dedicated, public-token-enabled event_registration schema
+    // per dev org, with a curated 5-field set, a draft submission, and a
+    // fully-submitted submission whose TAG_PICKER values exercise the
+    // SyncTagPickerSelectionsOnSubmit listener so user_organisation_tags
+    // populate during `migrate:fresh --seed`.
+    // =========================================================================
+
+    /**
+     * Showcase field definitions. 5 fields per Sprint 0.5 spec.
+     *
+     * @return list<array<string, mixed>>
+     */
+    private static function showcaseFieldDefinitions(): array
+    {
+        return [
+            [
+                'type' => FormFieldType::HEADING,
+                'slug' => 'over-jou',
+                'label' => 'Over jou',
+                'is_required' => false,
+                'is_filterable' => false,
+                'display_width' => 'full',
+                'value_storage_hint' => FormValueStorageHint::JSON,
+            ],
+            [
+                'type' => FormFieldType::SELECT,
+                'slug' => 'shirtmaat',
+                'label' => 'Shirtmaat',
+                'options' => ['XS', 'S', 'M', 'L', 'XL', 'XXL'],
+                'is_required' => true,
+                'is_filterable' => true,
+                'display_width' => 'half',
+                'value_storage_hint' => FormValueStorageHint::STRING,
+            ],
+            [
+                'type' => FormFieldType::CHECKBOX_LIST,
+                'slug' => 'dieetwensen',
+                'label' => 'Dieetwensen',
+                'options' => ['Vegetarisch', 'Veganistisch', 'Glutenvrij', 'Lactosevrij', 'Halal', 'Kosher'],
+                'is_required' => false,
+                'is_filterable' => true,
+                'display_width' => 'half',
+                'value_storage_hint' => FormValueStorageHint::JSON,
+            ],
+            [
+                'type' => FormFieldType::TAG_PICKER,
+                'slug' => 'vaardigheden',
+                'label' => 'Vaardigheden en certificaten',
+                // validation_rules.tag_categories = [] means "all active
+                // person_tags for this org" — the FormFieldResource picks
+                // up every active tag when no category filter is set.
+                'validation_rules' => null,
+                'is_required' => false,
+                'is_filterable' => true,
+                'display_width' => 'full',
+                'value_storage_hint' => FormValueStorageHint::JSON,
+            ],
+            [
+                'type' => FormFieldType::TEXTAREA,
+                'slug' => 'opmerkingen',
+                'label' => 'Opmerkingen',
+                'is_required' => false,
+                'is_filterable' => false,
+                'display_width' => 'full',
+                'value_storage_hint' => FormValueStorageHint::STRING,
+            ],
+        ];
+    }
+
+    /**
+     * Create the public-token-enabled showcase schema on the given primary
+     * event, plus its 5 fields. Returns the schema for follow-up seeding.
+     */
+    public static function seedEventRegistrationShowcaseSchema(Organisation $org, Event $event): FormSchema
+    {
+        $name = 'Vrijwilligersregistratie '.$event->name;
+        $slug = self::uniqueSchemaSlug($org, Str::slug($name));
+
+        /** @var FormSchema $schema */
+        $schema = FormSchema::create([
+            'organisation_id' => $org->id,
+            'owner_type' => 'event',
+            'owner_id' => $event->id,
+            'name' => $name,
+            'slug' => $slug,
+            'purpose' => FormPurpose::EVENT_REGISTRATION,
+            'description' => "Demo-formulier voor het end-to-end doorlopen van de vrijwilligersregistratie voor {$event->name}.",
+            'is_published' => true,
+            'submission_mode' => FormSubmissionMode::DRAFT_SINGLE,
+            'public_token' => (string) Str::ulid(),
+            'locale' => 'nl',
+            'snapshot_mode' => FormSchemaSnapshotMode::ON_SUBMIT,
+            'freeze_on_submit' => false,
+            'section_level_submit' => false,
+            'auto_save_enabled' => false,
+            'version' => 1,
+        ]);
+
+        foreach (self::showcaseFieldDefinitions() as $sortOrder => $def) {
+            FormField::create([
+                'form_schema_id' => $schema->id,
+                'field_type' => $def['type']->value,
+                'slug' => $def['slug'],
+                'label' => $def['label'],
+                'options' => $def['options'] ?? null,
+                'validation_rules' => $def['validation_rules'] ?? null,
+                'is_required' => $def['is_required'] ?? false,
+                'is_filterable' => $def['is_filterable'] ?? false,
+                'is_portal_visible' => true,
+                'is_admin_only' => false,
+                'is_pii' => false,
+                'display_width' => $def['display_width'] ?? 'full',
+                'binding' => null,
+                'role_restrictions' => null,
+                'value_storage_hint' => $def['value_storage_hint'] ?? FormValueStorageHint::JSON,
+                'sort_order' => $sortOrder + 1,
+            ]);
+        }
+
+        return $schema->refresh();
+    }
+
+    /**
+     * Seed one draft + one fully-submitted submission on the showcase
+     * schema. The submitted one triggers FormSubmissionSubmitted so the
+     * §31.10 listener runs and `user_organisation_tags` picks up
+     * `source=self_reported` rows for the submitter's user.
+     *
+     * Returns summary stats for caller-side logging.
+     *
+     * @return array{draft_person: ?Person, submitted_person: ?Person, synced_tag_count: int}
+     */
+    public static function seedEventRegistrationShowcaseSubmissions(FormSchema $schema, Organisation $org): array
+    {
+        $event = Event::withoutGlobalScopes()->find($schema->owner_id);
+        if ($event === null) {
+            return ['draft_person' => null, 'submitted_person' => null, 'synced_tag_count' => 0];
+        }
+
+        // Deterministic pick: first two approved persons with a user_id
+        // on this event, ordered by ULID (chronological insertion order).
+        $candidates = Person::withoutGlobalScopes()
+            ->where('event_id', $event->id)
+            ->whereNotNull('user_id')
+            ->orderBy('id')
+            ->take(2)
+            ->get();
+
+        $draftPerson = $candidates->first();
+        $submittedPerson = $candidates->skip(1)->first();
+
+        if ($draftPerson !== null) {
+            self::buildDraftSubmission($schema, $draftPerson);
+        }
+
+        $syncedTagCount = 0;
+        if ($submittedPerson !== null) {
+            $syncedTagCount = self::buildSubmittedSubmission($schema, $org, $submittedPerson);
+        }
+
+        return [
+            'draft_person' => $draftPerson,
+            'submitted_person' => $submittedPerson,
+            'synced_tag_count' => $syncedTagCount,
+        ];
+    }
+
+    /**
+     * Orchestration helper: schema + submissions + console output, matching
+     * the exact format Bert asked for in Sprint 0.5.
+     */
+    public static function seedEventRegistrationShowcase(
+        Organisation $org,
+        Event $event,
+        ?Command $command = null,
+    ): FormSchema {
+        $schema = self::seedEventRegistrationShowcaseSchema($org, $event);
+
+        $appUrl = rtrim((string) config('app.url'), '/');
+        $publicUrl = "{$appUrl}/api/v1/public/forms/{$schema->public_token}";
+
+        if ($command !== null) {
+            $command->info("[FormBuilderDevSeeder] Seeded event_registration schema for {$org->name}:");
+            $command->info("  public URL: {$publicUrl}");
+        }
+
+        $stats = self::seedEventRegistrationShowcaseSubmissions($schema, $org);
+
+        if ($command !== null) {
+            $draft = $stats['draft_person'];
+            if ($draft === null) {
+                $command->warn('[FormBuilderDevSeeder] No person with user_id found — draft submission skipped.');
+            } else {
+                $command->info("[FormBuilderDevSeeder] Draft registration stored for {$draft->full_name} (person {$draft->id})");
+            }
+
+            $submitted = $stats['submitted_person'];
+            if ($submitted === null) {
+                $command->warn('[FormBuilderDevSeeder] Not enough persons with user_id for submitted demo — §31.10 sync not exercised.');
+            } else {
+                $command->info("[FormBuilderDevSeeder] Submitted registration for {$submitted->full_name}");
+                $command->info("  TAG_PICKER sync result: {$stats['synced_tag_count']} self_reported tags now on user {$submitted->user_id}");
+            }
+        }
+
+        return $schema;
+    }
+
+    private static function buildDraftSubmission(FormSchema $schema, Person $person): FormSubmission
+    {
+        $fields = $schema->fields()->get()->keyBy('slug');
+
+        /** @var FormSubmission $submission */
+        $submission = FormSubmission::create([
+            'form_schema_id' => $schema->id,
+            'subject_type' => 'person',
+            'subject_id' => $person->id,
+            'submitted_by_user_id' => $person->user_id,
+            'status' => FormSubmissionStatus::DRAFT->value,
+            'is_test' => false,
+            'submitted_in_locale' => 'nl',
+            'opened_at' => now()->subDay(),
+        ]);
+
+        // Realistic partial fill — deliberately skip TAG_PICKER (that path
+        // is exercised by the submitted demo below).
+        self::createValueIfField($fields, 'shirtmaat', 'M', $submission);
+        self::createValueIfField($fields, 'dieetwensen', ['Vegetarisch'], $submission);
+
+        return $submission->refresh();
+    }
+
+    /**
+     * Full-submit path: create draft, fill values (incl. TAG_PICKER), run
+     * the service so FormSubmissionSubmitted fires and §31.10 runs. Queue
+     * connection is flipped to sync for the duration so the listener
+     * executes inline rather than being deferred to redis during seeding.
+     */
+    private static function buildSubmittedSubmission(FormSchema $schema, Organisation $org, Person $person): int
+    {
+        $tagIds = PersonTag::withoutGlobalScopes()
+            ->where('organisation_id', $org->id)
+            ->where('is_active', true)
+            ->orderBy('sort_order')
+            ->orderBy('name')
+            ->take(3)
+            ->pluck('id')
+            ->all();
+
+        /** @var FormSubmissionService $submissionService */
+        $submissionService = app(FormSubmissionService::class);
+
+        $submission = $submissionService->createDraft(
+            $schema,
+            $person,
+            $person->user,
+            [
+                'opened_at' => now()->subHours(2),
+                'is_test' => false,
+            ],
+        );
+
+        /** @var FormValueService $valueService */
+        $valueService = app(FormValueService::class);
+        $valueService->upsertMany(
+            $submission,
+            [
+                'shirtmaat' => 'L',
+                'dieetwensen' => ['Glutenvrij', 'Lactosevrij'],
+                'vaardigheden' => $tagIds,
+                'opmerkingen' => 'Kan eerder als nodig.',
+            ],
+            $person->user,
+        );
+
+        // Force synchronous listener execution while we're in the seeder
+        // so user_organisation_tags is populated by the time the migrate
+        // command returns (see `QUEUE_CONNECTION=redis` in local .env).
+        $previousConnection = config('queue.default');
+        config(['queue.default' => 'sync']);
+
+        try {
+            $submissionService->submit($submission->refresh(), $person->user);
+        } finally {
+            config(['queue.default' => $previousConnection]);
+        }
+
+        return UserOrganisationTag::query()
+            ->where('user_id', $person->user_id)
+            ->where('organisation_id', $org->id)
+            ->where('source', 'self_reported')
+            ->count();
+    }
+
+    private static function uniqueSchemaSlug(Organisation $org, string $base): string
+    {
+        $candidate = $base;
+        $i = 2;
+        while (FormSchema::withoutGlobalScopes()
+            ->where('organisation_id', $org->id)
+            ->where('slug', $candidate)
+            ->exists()
+        ) {
+            $candidate = $base.'-'.$i;
+            $i++;
+        }
+
+        return $candidate;
+    }
 }