feat(form-builder): public draft/save/submit split + sub-endpoints + validation

S2c D2, D3, D4, D8 — the meat of the public API rewrite.

Draft / save / submit split (D4):
- POST /public/forms/{public_token}/submissions
    Creates a draft. idempotency_key is now REQUIRED; second POST with
    the same key returns the existing draft (HTTP 200 vs 201 for fresh).
    UniqueConstraintViolationException caught for race-safe replay.
- PUT /public/forms/{public_token}/submissions/{submission_id}
    Auto-save. Partial updates only — each PUT writes just the
    slugs in the body. Status stays 'draft'; auto_save_count++.
- POST /public/forms/{public_token}/submissions/{submission_id}/submit
    Final submission. Merges body values with already-saved values,
    runs strict rule set against the merged map, then calls
    FormSubmissionService::submit which fires the lifecycle events
    (tag sync, identity match). Rate-limited per IP per token per hour.

Access rules: submission must belong to the resolved schema; status
must be 'draft' (409 SUBMISSION_ALREADY_SUBMITTED otherwise); schema
still accepting submissions.

Sub-endpoints (D2, D3):
- GET /public/forms/{public_token}/time-slots
    Volunteer-only, festival-aware (parent + children). Reads straight
    from TimeSlot model — no org-coupled service to extract from. Out:
    {id, name, date, start_time, end_time, duration_hours, event_id,
    event_name}.
- GET /public/forms/{public_token}/sections
    show_in_registration=true, type=standard, deduplicated by name
    across festival children.

Dynamic per-field validation (D8):
- FormFieldRuleBuilder builds Laravel rule arrays from form_fields.
  strict() enforces is_required + in:options + type rules (email,
  url, numeric, date, boolean, phone regex); relaxed() is the
  auto-save variant that drops required-ness.
- StartPublicDraftRequest (required idempotency_key),
  SavePublicDraftRequest (relaxed rules, values optional),
  SubmitPublicSubmissionRequest (relaxed rules at body level — the
  controller merges the body with saved values and runs the strict
  validator on the full map so submit with an empty body still
  passes when everything was auto-saved).
- FormValueService backs the request layer up with deeper enforcement
  of validation_rules JSON (min/max/regex) + is_unique. Throws
  FieldValidationException (422) which renders via the D6 envelope.

PublicFormTokenResolver centralises the grace-window logic; every
public endpoint resolves through it so the standardised exceptions
bubble uniformly.

Routes: 6 total under /public/forms/ (up from 2). Tests:
PublicFormApiTest's existing submit test retrofitted to the three-step
flow; 857 tests still green.

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

api/app/Http/Controllers/Api/V1/FormBuilder/PublicFormController.php

@@ -5,142 +5,132 @@ declare(strict_types=1);
 namespace App\Http\Controllers\Api\V1\FormBuilder;
 
 use App\Http\Controllers\Controller;
-use App\Http\Requests\Api\V1\FormBuilder\PublicSubmissionRequest;
-use App\Http\Resources\FormBuilder\FormSubmissionResource;
 use App\Http\Resources\FormBuilder\PublicFormSchemaResource;
+use App\Models\Event;
+use App\Models\FestivalSection;
 use App\Models\FormBuilder\FormSchema;
-use App\Services\FormBuilder\FormSubmissionService;
+use App\Models\TimeSlot;
+use App\Services\FormBuilder\PublicFormTokenResolver;
 use Illuminate\Http\JsonResponse;
-use Illuminate\Http\Request;
-use Illuminate\Support\Facades\Http;
-use Illuminate\Support\Facades\RateLimiter;
+use Illuminate\Support\Collection;
 
+/**
+ * Public read-side endpoints for the form builder:
+ *   - GET  /public/forms/{public_token}                    schema + fields + tag options
+ *   - GET  /public/forms/{public_token}/time-slots         AVAILABILITY_PICKER dependency data
+ *   - GET  /public/forms/{public_token}/sections           SECTION_PRIORITY dependency data
+ *
+ * Draft/save/submit live in PublicFormSubmissionController.
+ */
 final class PublicFormController extends Controller
 {
     public function __construct(
-        private readonly FormSubmissionService $submissionService,
+        private readonly PublicFormTokenResolver $tokenResolver,
     ) {}
 
     public function show(string $publicToken): JsonResponse
     {
-        $schema = $this->resolveSchema($publicToken, $grace);
-        if ($schema === null) {
-            return $this->error('Form not found.', 404);
-        }
-        if ($grace === 'expired') {
-            return $this->error('This form link has expired.', 410);
-        }
+        $schema = $this->tokenResolver->resolve($publicToken);
 
         return $this->success(new PublicFormSchemaResource($schema));
     }
 
-    public function submit(PublicSubmissionRequest $request, string $publicToken): JsonResponse
+    public function timeSlots(string $publicToken): JsonResponse
     {
-        $schema = $this->resolveSchema($publicToken, $grace);
-        if ($schema === null) {
-            return $this->error('Form not found.', 404);
-        }
-        if ($grace === 'expired') {
-            return $this->error('This form link has expired.', 410);
-        }
-        if (! $schema->is_published) {
-            return $this->error('Form is not currently accepting submissions.', 410);
+        $schema = $this->tokenResolver->resolve($publicToken);
+        $event = $this->ownerEvent($schema);
+        if ($event === null) {
+            return $this->success(['data' => []]);
         }
 
-        $purpose = $schema->purpose instanceof \BackedEnum ? $schema->purpose->value : (string) $schema->purpose;
-        $captchaRequired = in_array($purpose, (array) config('form_builder.captcha.required_for_purposes', []), true);
-        if ($captchaRequired && ! $this->captchaValid($request)) {
-            return $this->error('Captcha validation failed.', 422);
+        $eventIds = $this->festivalEventIds($event);
+
+        $slots = TimeSlot::query()
+            ->whereIn('event_id', $eventIds)
+            ->where('person_type', 'VOLUNTEER')
+            ->with(['event:id,name'])
+            ->orderBy('date')
+            ->orderBy('start_time')
+            ->get();
+
+        return response()->json([
+            'data' => $slots->map(fn (TimeSlot $ts) => [
+                'id' => (string) $ts->id,
+                'name' => (string) $ts->name,
+                'date' => optional($ts->date)->toDateString(),
+                'start_time' => (string) $ts->start_time,
+                'end_time' => (string) $ts->end_time,
+                'duration_hours' => $ts->duration_hours !== null ? (float) $ts->duration_hours : null,
+                'event_id' => (string) $ts->event_id,
+                'event_name' => (string) ($ts->event?->name ?? ''),
+            ])->values()->all(),
+        ]);
     }
 
-        $key = 'form-submit:'.$publicToken.':'.$request->ip();
-        $perHour = (int) config('form_builder.limits.max_submissions_per_public_schema_per_ip_per_hour', 5);
-        if (RateLimiter::tooManyAttempts($key, $perHour)) {
-            return response()
-                ->json(['success' => false, 'message' => 'Too many submissions.'], 429)
-                ->header('Retry-After', (string) RateLimiter::availableIn($key));
-        }
-        RateLimiter::hit($key, 3600);
-
-        $submission = $this->submissionService->createDraft(
-            $schema,
-            null,
-            $request->user(),
-            [
-                'idempotency_key' => $request->validated('idempotency_key'),
-                'is_test' => false,
-                'public_submitter_name' => $request->validated('public_submitter_name'),
-                'public_submitter_email' => $request->validated('public_submitter_email'),
-                'public_submitter_ip' => $request->ip(),
-            ],
-        );
-
-        $values = (array) ($request->validated('values') ?? []);
-        if ($values !== []) {
-            $this->submissionService->saveDraft($submission, $values, $request->user());
-        }
-
-        $submission = $this->submissionService->submit($submission->refresh(), $request->user());
-
-        return $this->created(new FormSubmissionResource($submission));
-    }
-
-    /**
-     * @param-out string|null $grace  'current' | 'previous' | 'expired' | null
-     */
-    private function resolveSchema(string $token, ?string &$grace = null): ?FormSchema
+    public function sections(string $publicToken): JsonResponse
     {
-        $grace = null;
-
-        $current = FormSchema::query()->where('public_token', $token)->first();
-        if ($current !== null) {
-            $grace = 'current';
-
-            return $current;
+        $schema = $this->tokenResolver->resolve($publicToken);
+        $event = $this->ownerEvent($schema);
+        if ($event === null) {
+            return $this->success(['data' => []]);
         }
 
-        $previous = FormSchema::query()->where('public_token_previous', $token)->first();
-        if ($previous === null) {
+        $eventIds = $this->festivalEventIds($event);
+
+        $sections = FestivalSection::query()
+            ->whereIn('event_id', $eventIds)
+            ->where('show_in_registration', true)
+            ->where('type', 'standard')
+            ->orderBy('sort_order')
+            ->orderBy('name')
+            ->get();
+
+        // For festival parents: dedup by name across children. Keep the
+        // first occurrence per name (lowest sort_order wins via the
+        // existing ordering).
+        $deduped = $sections->unique('name')->values();
+
+        return response()->json([
+            'data' => $deduped->map(fn (FestivalSection $s) => [
+                'id' => (string) $s->id,
+                'name' => (string) $s->name,
+                'category' => $s->category !== null ? (string) $s->category : null,
+                'icon' => $s->icon !== null ? (string) $s->icon : null,
+                'registration_description' => $s->registration_description !== null
+                    ? (string) $s->registration_description
+                    : null,
+            ])->all(),
+        ]);
+    }
+
+    private function ownerEvent(FormSchema $schema): ?Event
+    {
+        if ($schema->owner_type !== 'event' || $schema->owner_id === null) {
             return null;
         }
 
-        $rotatedAt = $previous->public_token_rotated_at;
-        if ($rotatedAt === null) {
-            $grace = 'previous';
-
-            return $previous;
+        return Event::withoutGlobalScopes()->find($schema->owner_id);
     }
 
-        $graceDays = 7;
-        if ($rotatedAt->addDays($graceDays)->isPast()) {
-            $grace = 'expired';
-
-            return $previous;
-        }
-
-        $grace = 'previous';
-
-        return $previous;
-    }
-
-    private function captchaValid(Request $request): bool
+    /**
+     * Festival-aware event id list: for a festival/series parent, returns
+     * the children (operational units where time_slots + festival_sections
+     * typically live). For a flat event or a sub-event, returns just its
+     * own id.
+     *
+     * @return array<int, string>
+     */
+    private function festivalEventIds(Event $event): array
     {
-        $token = (string) $request->input('captcha_token', '');
-        $secret = (string) config('form_builder.captcha.secret_key', '');
-        if ($token === '' || $secret === '') {
-            return false;
-        }
+        $childIds = Event::query()
+            ->where('parent_event_id', $event->id)
+            ->pluck('id')
+            ->map(fn ($id) => (string) $id)
+            ->all();
 
-        try {
-            $response = Http::asForm()->timeout(5)->post('https://challenges.cloudflare.com/turnstile/v0/siteverify', [
-                'secret' => $secret,
-                'response' => $token,
-                'remoteip' => $request->ip(),
-            ]);
-
-            return (bool) data_get($response->json(), 'success', false);
-        } catch (\Throwable) {
-            return false;
-        }
+        // Parent + children. For flat events $childIds is [] and the
+        // parent alone covers it. For festivals both parent-level
+        // cross-event items and per-child items surface.
+        return array_values(array_unique(array_merge([(string) $event->id], $childIds)));
     }
 }

api/app/Http/Controllers/Api/V1/FormBuilder/PublicFormSubmissionController.php

@@ -0,0 +1,238 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Controllers\Api\V1\FormBuilder;
+
+use App\Exceptions\FormBuilder\FieldValidationException;
+use App\Exceptions\FormBuilder\RateLimitedException;
+use App\Exceptions\FormBuilder\SchemaUnpublishedException;
+use App\Exceptions\FormBuilder\SubmissionAlreadySubmittedException;
+use App\Http\Controllers\Controller;
+use App\Http\Requests\Api\V1\FormBuilder\SavePublicDraftRequest;
+use App\Http\Requests\Api\V1\FormBuilder\StartPublicDraftRequest;
+use App\Http\Requests\Api\V1\FormBuilder\SubmitPublicSubmissionRequest;
+use App\Http\Resources\FormBuilder\PublicFormSubmissionResource;
+use App\Models\FormBuilder\FormSchema;
+use App\Models\FormBuilder\FormSubmission;
+use App\Enums\FormBuilder\FormSubmissionStatus;
+use App\Services\FormBuilder\FormFieldRuleBuilder;
+use App\Services\FormBuilder\FormSubmissionService;
+use App\Services\FormBuilder\FormValueService;
+use App\Services\FormBuilder\PublicFormTokenResolver;
+use Illuminate\Database\UniqueConstraintViolationException;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Http;
+use Illuminate\Support\Facades\RateLimiter;
+use Illuminate\Support\Facades\Validator;
+
+/**
+ * Public submission lifecycle: draft → save → submit. Each step is its
+ * own request method (S2c D4). Controller is deliberately thin — all
+ * business logic lives in FormSubmissionService / FormValueService.
+ */
+final class PublicFormSubmissionController extends Controller
+{
+    public function __construct(
+        private readonly PublicFormTokenResolver $tokenResolver,
+        private readonly FormSubmissionService $submissionService,
+        private readonly FormValueService $valueService,
+        private readonly FormFieldRuleBuilder $ruleBuilder,
+    ) {}
+
+    public function store(StartPublicDraftRequest $request, string $publicToken): JsonResponse
+    {
+        $schema = $this->tokenResolver->resolve($publicToken);
+        $this->assertAcceptingSubmissions($schema);
+
+        $context = [
+            'idempotency_key' => $request->validated('idempotency_key'),
+            'opened_at' => $request->validated('opened_at'),
+            'public_submitter_name' => $request->validated('public_submitter_name'),
+            'public_submitter_email' => $request->validated('public_submitter_email'),
+            'public_submitter_ip' => $request->ip(),
+            'is_test' => false,
+        ];
+
+        try {
+            $submission = $this->submissionService->createDraft($schema, null, null, $context);
+            $wasExisting = $submission->wasRecentlyCreated === false;
+        } catch (UniqueConstraintViolationException) {
+            // Race with a sibling request using the same idempotency key —
+            // re-read the existing draft.
+            $submission = FormSubmission::query()
+                ->where('form_schema_id', $schema->id)
+                ->where('idempotency_key', $context['idempotency_key'])
+                ->firstOrFail();
+            $wasExisting = true;
+        }
+
+        $status = $wasExisting ? 200 : 201;
+
+        return response()->json(
+            (new PublicFormSubmissionResource($submission))->response($request)->getData(),
+            $status,
+        );
+    }
+
+    public function update(SavePublicDraftRequest $request, string $publicToken, string $submissionId): JsonResponse
+    {
+        $schema = $this->tokenResolver->resolve($publicToken);
+        $this->assertAcceptingSubmissions($schema);
+
+        $submission = $this->loadSubmission($schema, $submissionId);
+        $this->assertDraft($submission);
+
+        $values = (array) ($request->validated('values') ?? []);
+        if ($values !== []) {
+            // Service throws FieldValidationException (422) on validation
+            // failure; the handler renders the standardised envelope.
+            $this->valueService->upsertMany($submission, $values, null);
+        }
+
+        if ($request->filled('first_interacted_at')) {
+            $submission->first_interacted_at ??= $request->validated('first_interacted_at');
+            $submission->save();
+        }
+
+        return $this->success(new PublicFormSubmissionResource($submission->fresh()));
+    }
+
+    public function submit(
+        SubmitPublicSubmissionRequest $request,
+        string $publicToken,
+        string $submissionId,
+    ): JsonResponse {
+        $schema = $this->tokenResolver->resolve($publicToken);
+        $this->assertAcceptingSubmissions($schema);
+
+        $submission = $this->loadSubmission($schema, $submissionId);
+        $this->assertDraft($submission);
+
+        $this->enforceRateLimit($schema, $publicToken, $request->ip());
+
+        $purpose = $schema->purpose instanceof \BackedEnum
+            ? $schema->purpose->value
+            : (string) $schema->purpose;
+        $captchaRequired = in_array($purpose, (array) config('form_builder.captcha.required_for_purposes', []), true);
+        if ($captchaRequired && ! $this->captchaValid($request)) {
+            throw new FieldValidationException(
+                ['captcha_token' => ['Captcha validation failed.']],
+                'Captcha validation failed.',
+            );
+        }
+
+        $bodyValues = (array) ($request->validated('values') ?? []);
+        $mergedValues = $this->mergeWithSavedValues($submission, $bodyValues);
+
+        $this->validateMergedValues($schema, $mergedValues);
+
+        if ($bodyValues !== []) {
+            $this->valueService->upsertMany($submission, $bodyValues, null);
+        }
+
+        $submission = $this->submissionService->submit($submission->refresh(), null);
+        RateLimiter::hit('form-submit:'.$publicToken.':'.$request->ip(), 3600);
+
+        return $this->created(new PublicFormSubmissionResource($submission));
+    }
+
+    private function loadSubmission(FormSchema $schema, string $submissionId): FormSubmission
+    {
+        /** @var FormSubmission|null $submission */
+        $submission = FormSubmission::query()
+            ->where('form_schema_id', $schema->id)
+            ->whereKey($submissionId)
+            ->first();
+
+        if ($submission === null) {
+            abort(response()->json([
+                'message' => 'Submission not found for this form.',
+                'code' => 'SUBMISSION_NOT_FOUND',
+            ], 404));
+        }
+
+        return $submission;
+    }
+
+    private function assertAcceptingSubmissions(FormSchema $schema): void
+    {
+        if (! (bool) $schema->is_published) {
+            throw new SchemaUnpublishedException;
+        }
+    }
+
+    private function assertDraft(FormSubmission $submission): void
+    {
+        $status = $submission->status instanceof \BackedEnum
+            ? $submission->status->value
+            : (string) $submission->status;
+
+        if ($status !== FormSubmissionStatus::DRAFT->value) {
+            throw new SubmissionAlreadySubmittedException;
+        }
+    }
+
+    private function enforceRateLimit(FormSchema $schema, string $publicToken, string $ip): void
+    {
+        $key = 'form-submit:'.$publicToken.':'.$ip;
+        $perHour = (int) config('form_builder.limits.max_submissions_per_public_schema_per_ip_per_hour', 5);
+        if (RateLimiter::tooManyAttempts($key, $perHour)) {
+            throw new RateLimitedException(RateLimiter::availableIn($key));
+        }
+    }
+
+    /**
+     * @param  array<string, mixed>  $bodyValues
+     * @return array<string, mixed>
+     */
+    private function mergeWithSavedValues(FormSubmission $submission, array $bodyValues): array
+    {
+        $saved = [];
+        foreach ($submission->values()->with('field')->get() as $value) {
+            $slug = $value->field?->slug;
+            if ($slug !== null) {
+                $saved[$slug] = $value->value;
+            }
+        }
+
+        return array_merge($saved, $bodyValues);
+    }
+
+    /**
+     * @param  array<string, mixed>  $merged
+     */
+    private function validateMergedValues(FormSchema $schema, array $merged): void
+    {
+        $rules = $this->ruleBuilder->strict($schema);
+        // Extend body wrapper rule so the merged `values` array passes.
+        $rules['values'] = ['required', 'array'];
+
+        $validator = Validator::make(['values' => $merged], $rules);
+        if ($validator->fails()) {
+            throw new FieldValidationException($validator->errors()->messages());
+        }
+    }
+
+    private function captchaValid(Request $request): bool
+    {
+        $token = (string) $request->input('captcha_token', '');
+        $secret = (string) config('form_builder.captcha.secret_key', '');
+        if ($token === '' || $secret === '') {
+            return false;
+        }
+
+        try {
+            $response = Http::asForm()->timeout(5)->post('https://challenges.cloudflare.com/turnstile/v0/siteverify', [
+                'secret' => $secret,
+                'response' => $token,
+                'remoteip' => $request->ip(),
+            ]);
+
+            return (bool) data_get($response->json(), 'success', false);
+        } catch (\Throwable) {
+            return false;
+        }
+    }
+}

api/app/Http/Requests/Api/V1/FormBuilder/SavePublicDraftRequest.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Requests\Api\V1\FormBuilder;
+
+use App\Models\FormBuilder\FormSchema;
+use App\Services\FormBuilder\FormFieldRuleBuilder;
+use App\Services\FormBuilder\PublicFormTokenResolver;
+use Illuminate\Foundation\Http\FormRequest;
+
+/**
+ * Body for `PUT /api/v1/public/forms/{public_token}/submissions/{id}`.
+ * Auto-save endpoint — relaxed rule set per S2c D8. Only the field
+ * slugs present in the body are written; everything is nullable.
+ */
+final class SavePublicDraftRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function rules(): array
+    {
+        $base = [
+            'values' => ['sometimes', 'array'],
+            'first_interacted_at' => ['nullable', 'date'],
+        ];
+
+        $schema = $this->resolveSchema();
+        if (! $schema instanceof FormSchema) {
+            return $base;
+        }
+
+        return array_merge(
+            $base,
+            app(FormFieldRuleBuilder::class)->relaxed($schema),
+        );
+    }
+
+    private function resolveSchema(): ?FormSchema
+    {
+        $token = (string) $this->route('public_token');
+        if ($token === '') {
+            return null;
+        }
+        try {
+            return app(PublicFormTokenResolver::class)->resolve($token);
+        } catch (\Throwable) {
+            return null;
+        }
+    }
+}

api/app/Http/Requests/Api/V1/FormBuilder/StartPublicDraftRequest.php

@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Requests\Api\V1\FormBuilder;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+/**
+ * Body for `POST /api/v1/public/forms/{public_token}/submissions` (S2c D4).
+ * Creates a draft. Contains no field values — values are written later
+ * via PUT (auto-save) or POST /submit.
+ *
+ * `idempotency_key` is REQUIRED: duplicate POSTs with the same key must
+ * return the existing draft rather than create a second one.
+ */
+final class StartPublicDraftRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function rules(): array
+    {
+        return [
+            'idempotency_key' => ['required', 'string', 'min:6', 'max:30'],
+            'opened_at' => ['nullable', 'date'],
+            'submitted_in_locale' => ['nullable', 'string', 'max:10'],
+            'public_submitter_name' => ['nullable', 'string', 'max:150'],
+            'public_submitter_email' => ['nullable', 'email', 'max:255'],
+        ];
+    }
+}

api/app/Http/Requests/Api/V1/FormBuilder/SubmitPublicSubmissionRequest.php

@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Requests\Api\V1\FormBuilder;
+
+use App\Models\FormBuilder\FormSchema;
+use App\Services\FormBuilder\FormFieldRuleBuilder;
+use App\Services\FormBuilder\PublicFormTokenResolver;
+use Illuminate\Foundation\Http\FormRequest;
+
+/**
+ * Body for `POST /api/v1/public/forms/{public_token}/submissions/{id}/submit`.
+ *
+ * The FormRequest validates the request body in isolation using the
+ * *relaxed* rule set, because the controller merges the body with any
+ * values already saved via earlier PUT calls and runs the strict rule
+ * set on the merged value map before actually submitting.
+ *
+ * Upshot: a submit call with an empty body but all values auto-saved
+ * during drafting still passes at the request layer.
+ */
+final class SubmitPublicSubmissionRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function rules(): array
+    {
+        $base = [
+            'values' => ['sometimes', 'array'],
+            'captcha_token' => ['nullable', 'string', 'max:2000'],
+        ];
+
+        $schema = $this->resolveSchema();
+        if (! $schema instanceof FormSchema) {
+            return $base;
+        }
+
+        return array_merge(
+            $base,
+            app(FormFieldRuleBuilder::class)->relaxed($schema),
+        );
+    }
+
+    private function resolveSchema(): ?FormSchema
+    {
+        $token = (string) $this->route('public_token');
+        if ($token === '') {
+            return null;
+        }
+        try {
+            return app(PublicFormTokenResolver::class)->resolve($token);
+        } catch (\Throwable) {
+            return null;
+        }
+    }
+}

api/app/Services/FormBuilder/FormFieldRuleBuilder.php

@@ -0,0 +1,210 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Services\FormBuilder;
+
+use App\Enums\FormBuilder\FormFieldType;
+use App\Models\FormBuilder\FormField;
+use App\Models\FormBuilder\FormSchema;
+
+/**
+ * Build Laravel validation rules dynamically from a schema's form_fields.
+ *
+ * Two modes (S2c D8):
+ *   - strict(): for the final submit pipeline. is_required fields are
+ *     required; SELECT/RADIO values must be in options; multi-value
+ *     types must be arrays; type rules (email/url/date/numeric/boolean)
+ *     are enforced.
+ *   - relaxed(): for auto-save drafts. Every rule becomes nullable;
+ *     options lists still constrain (a SELECT can't silently accept
+ *     garbage, even mid-draft), but required stays off.
+ *
+ * Rule shape returned targets `values.{slug}` and `values.{slug}.*` keys
+ * so FormRequests can merge this into their own `values` wrapper:
+ *
+ *     return array_merge(['values' => ['required', 'array']], $ruleBuilder->strict($schema));
+ */
+final class FormFieldRuleBuilder
+{
+    /**
+     * @return array<string, array<int, string>>
+     */
+    public function strict(FormSchema $schema): array
+    {
+        return $this->build($schema, strict: true);
+    }
+
+    /**
+     * @return array<string, array<int, string>>
+     */
+    public function relaxed(FormSchema $schema): array
+    {
+        return $this->build($schema, strict: false);
+    }
+
+    /**
+     * @return array<string, array<int, string>>
+     */
+    private function build(FormSchema $schema, bool $strict): array
+    {
+        $fields = $schema->fields()->get();
+        $rules = [];
+
+        foreach ($fields as $field) {
+            if (! (bool) $field->is_portal_visible || (bool) $field->is_admin_only) {
+                continue;
+            }
+
+            if (in_array($field->field_type, [FormFieldType::HEADING->value, FormFieldType::PARAGRAPH->value], true)) {
+                continue;
+            }
+
+            $key = 'values.'.$field->slug;
+            $isMulti = $this->isMultiValue($field);
+            $primaryRules = [];
+
+            if ($strict && (bool) $field->is_required) {
+                $primaryRules[] = $isMulti ? 'present' : 'required';
+            } else {
+                $primaryRules[] = 'sometimes';
+                $primaryRules[] = 'nullable';
+            }
+
+            if ($isMulti) {
+                $primaryRules[] = 'array';
+                $rules[$key] = $primaryRules;
+
+                foreach ($this->itemRulesFor($field, $strict) as $itemRule) {
+                    $rules[$key.'.*'][] = $itemRule;
+                }
+                continue;
+            }
+
+            foreach ($this->scalarTypeRules($field) as $r) {
+                $primaryRules[] = $r;
+            }
+            foreach ($this->validationRuleShortcuts($field) as $r) {
+                $primaryRules[] = $r;
+            }
+
+            $rules[$key] = $primaryRules;
+        }
+
+        return $rules;
+    }
+
+    private function isMultiValue(FormField $field): bool
+    {
+        return in_array($field->field_type, [
+            FormFieldType::MULTISELECT->value,
+            FormFieldType::CHECKBOX_LIST->value,
+            FormFieldType::TAG_PICKER->value,
+            FormFieldType::AVAILABILITY_PICKER->value,
+            FormFieldType::SECTION_PRIORITY->value,
+            FormFieldType::TABLE_ROWS->value,
+        ], true);
+    }
+
+    /**
+     * @return array<int, string>
+     */
+    private function scalarTypeRules(FormField $field): array
+    {
+        return match ($field->field_type) {
+            FormFieldType::EMAIL->value => ['email:rfc'],
+            FormFieldType::URL->value => ['url'],
+            FormFieldType::NUMBER->value => ['numeric'],
+            FormFieldType::DATE->value => ['date_format:Y-m-d'],
+            FormFieldType::DATETIME->value => ['date'],
+            FormFieldType::BOOLEAN->value => ['boolean'],
+            FormFieldType::PHONE->value => ['regex:/^[+]?[0-9\s\-()]{4,25}$/'],
+            FormFieldType::SELECT->value, FormFieldType::RADIO->value => $this->inOptionsRule($field),
+            default => ['string'],
+        };
+    }
+
+    /**
+     * @return array<int, string>
+     */
+    private function itemRulesFor(FormField $field, bool $strict): array
+    {
+        $rules = [];
+        if ($strict && (bool) $field->is_required) {
+            $rules[] = 'required';
+        } else {
+            $rules[] = 'nullable';
+        }
+
+        return match ($field->field_type) {
+            FormFieldType::MULTISELECT->value, FormFieldType::CHECKBOX_LIST->value => array_merge($rules, $this->inOptionsRule($field)),
+            FormFieldType::TAG_PICKER->value => array_merge($rules, ['string', 'max:30']),
+            FormFieldType::AVAILABILITY_PICKER->value => array_merge($rules, ['string', 'max:30']),
+            FormFieldType::SECTION_PRIORITY->value => array_merge($rules, ['array:section_id,priority']),
+            FormFieldType::TABLE_ROWS->value => array_merge($rules, ['array']),
+            default => $rules,
+        };
+    }
+
+    /**
+     * @return array<int, string>
+     */
+    private function inOptionsRule(FormField $field): array
+    {
+        $options = $this->scalarOptions($field);
+        if ($options === []) {
+            return [];
+        }
+
+        return ['in:'.implode(',', $options)];
+    }
+
+    /**
+     * @return array<int, string>
+     */
+    private function scalarOptions(FormField $field): array
+    {
+        $options = is_array($field->options) ? $field->options : [];
+        $out = [];
+        foreach ($options as $opt) {
+            if (is_scalar($opt)) {
+                $out[] = (string) $opt;
+            } elseif (is_array($opt) && isset($opt['value']) && is_scalar($opt['value'])) {
+                $out[] = (string) $opt['value'];
+            } elseif (is_array($opt) && isset($opt['label']) && is_scalar($opt['label'])) {
+                $out[] = (string) $opt['label'];
+            }
+        }
+
+        return $out;
+    }
+
+    /**
+     * Shortcuts picked up from form_fields.validation_rules JSON.
+     * Service-layer FormValueService does the deeper min/max/regex/unique
+     * enforcement — these are quick boundary checks surfaced at the
+     * Request layer when cheap.
+     *
+     * @return array<int, string>
+     */
+    private function validationRuleShortcuts(FormField $field): array
+    {
+        $rules = [];
+        $v = $field->validation_rules ?? null;
+        if (! is_array($v)) {
+            return $rules;
+        }
+
+        if (isset($v['min']) && is_numeric($v['min'])) {
+            $rules[] = 'min:'.(string) $v['min'];
+        }
+        if (isset($v['max']) && is_numeric($v['max'])) {
+            $rules[] = 'max:'.(string) $v['max'];
+        }
+        if (isset($v['regex']) && is_string($v['regex'])) {
+            $rules[] = 'regex:'.$v['regex'];
+        }
+
+        return $rules;
+    }
+}

api/app/Services/FormBuilder/FormValueService.php

@@ -37,7 +37,9 @@ final class FormValueService
             ->get()
             ->keyBy('slug');
 
-        DB::transaction(function () use ($slugToValue, $fields, $submission, $actor): void {
+        $fieldErrors = [];
+
+        DB::transaction(function () use ($slugToValue, $fields, $submission, $actor, &$fieldErrors): void {
             foreach ($slugToValue as $slug => $raw) {
                 $field = $fields->get($slug);
                 if ($field === null) {
@@ -53,10 +55,68 @@ final class FormValueService
                     throw new AuthorizationException(sprintf('Not allowed to write field "%s".', $slug));
                 }
 
+                $errors = $this->validateAgainstFieldRules($field, $raw, $submission);
+                if ($errors !== []) {
+                    $fieldErrors[$slug] = $errors;
+
+                    continue;
+                }
+
                 $this->writeValue($submission, $field, $raw);
                 $this->writeEntityMirror($submission, $field, $raw);
             }
         });
+
+        if ($fieldErrors !== []) {
+            throw new \App\Exceptions\FormBuilder\FieldValidationException($fieldErrors);
+        }
+    }
+
+    /**
+     * Backstop enforcement of form_fields.validation_rules JSON per
+     * S2c D8. The FormFieldRuleBuilder already surfaces min/max/regex
+     * shortcuts at the request layer; this is where the deeper checks
+     * (is_unique, validation_rules.unique) live.
+     *
+     * @return array<int, string>
+     */
+    private function validateAgainstFieldRules(FormField $field, mixed $raw, FormSubmission $submission): array
+    {
+        $errors = [];
+        $rules = is_array($field->validation_rules) ? $field->validation_rules : [];
+
+        if ($raw === null || $raw === '' || $raw === []) {
+            return $errors;
+        }
+
+        if (isset($rules['min']) && is_numeric($rules['min']) && is_numeric($raw) && (float) $raw < (float) $rules['min']) {
+            $errors[] = sprintf('Minimum is %s.', (string) $rules['min']);
+        }
+        if (isset($rules['max']) && is_numeric($rules['max']) && is_numeric($raw) && (float) $raw > (float) $rules['max']) {
+            $errors[] = sprintf('Maximum is %s.', (string) $rules['max']);
+        }
+        if (isset($rules['regex']) && is_string($rules['regex']) && is_string($raw)
+            && @preg_match($rules['regex'], $raw) !== 1) {
+            $errors[] = 'Value does not match the expected format.';
+        }
+
+        $unique = (bool) $field->is_unique || (bool) ($rules['unique'] ?? false);
+        if ($unique) {
+            $scalar = is_scalar($raw) ? (string) $raw : null;
+            if ($scalar !== null) {
+                $exists = \App\Models\FormBuilder\FormValue::query()
+                    ->where('form_field_id', $field->id)
+                    ->where('value_indexed', $scalar)
+                    ->where('form_submission_id', '!=', $submission->id)
+                    ->whereHas('submission', fn ($q) => $q->where('status', \App\Enums\FormBuilder\FormSubmissionStatus::SUBMITTED->value))
+                    ->exists();
+                if ($exists) {
+                    $errors[] = 'This value is already in use for another submission.';
+                }
+            }
+        }
+
+        return $errors;
     }
 
     private function writeValue(FormSubmission $submission, FormField $field, mixed $raw): void

api/app/Services/FormBuilder/PublicFormTokenResolver.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Services\FormBuilder;
+
+use App\Exceptions\FormBuilder\SchemaNotFoundException;
+use App\Exceptions\FormBuilder\TokenExpiredException;
+use App\Models\FormBuilder\FormSchema;
+
+/**
+ * Token-to-schema resolution for every /public/forms/* endpoint.
+ * Centralises the 7-day grace window logic (ARCH §10, BACKLOG FORM-04
+ * tracks making this configurable).
+ *
+ * Throws the standardised public-form exceptions directly so callers
+ * don't need to branch on grace state themselves.
+ */
+final class PublicFormTokenResolver
+{
+    private const GRACE_DAYS = 7;
+
+    public function resolve(string $token): FormSchema
+    {
+        $current = FormSchema::query()
+            ->where('public_token', $token)
+            ->first();
+        if ($current !== null) {
+            return $current;
+        }
+
+        $previous = FormSchema::query()
+            ->where('public_token_previous', $token)
+            ->first();
+
+        if ($previous === null) {
+            throw new SchemaNotFoundException;
+        }
+
+        $rotatedAt = $previous->public_token_rotated_at;
+        if ($rotatedAt === null) {
+            return $previous;
+        }
+
+        if ($rotatedAt->addDays(self::GRACE_DAYS)->isPast()) {
+            throw new TokenExpiredException;
+        }
+
+        return $previous;
+    }
+}

api/routes/api.php

@@ -97,10 +97,25 @@ Route::post('verify-email-change', [EmailChangeController::class, 'verify']);
 Route::post('public/check-email', CheckEmailController::class)->middleware('throttle:10,1');
 Route::post('portal/token-auth', [PortalTokenController::class, 'auth'])->middleware('throttle:10,1');
 
-// Public Form Builder routes (no auth — token-based, rate-limited per ARCH §10)
+// Public Form Builder routes (no auth — token-based, rate-limited per ARCH §10).
+// S2c D4: draft/save/submit split into three separate endpoints.
 Route::middleware('throttle:30,1')->group(function (): void {
     Route::get('public/forms/{public_token}', [PublicFormController::class, 'show']);
-    Route::post('public/forms/{public_token}/submissions', [PublicFormController::class, 'submit']);
+    Route::get('public/forms/{public_token}/time-slots', [PublicFormController::class, 'timeSlots']);
+    Route::get('public/forms/{public_token}/sections', [PublicFormController::class, 'sections']);
+
+    Route::post(
+        'public/forms/{public_token}/submissions',
+        [\App\Http\Controllers\Api\V1\FormBuilder\PublicFormSubmissionController::class, 'store'],
+    );
+    Route::put(
+        'public/forms/{public_token}/submissions/{submission_id}',
+        [\App\Http\Controllers\Api\V1\FormBuilder\PublicFormSubmissionController::class, 'update'],
+    );
+    Route::post(
+        'public/forms/{public_token}/submissions/{submission_id}/submit',
+        [\App\Http\Controllers\Api\V1\FormBuilder\PublicFormSubmissionController::class, 'submit'],
+    );
 });
 
 // Platform Admin routes

api/tests/Feature/FormBuilder/PublicFormApiTest.php

@@ -73,17 +73,30 @@ final class PublicFormApiTest extends TestCase
         // PUBLIC_RSVP does not require captcha by default
         Config::set('form_builder.captcha.required_for_purposes', []);
 
-        $response = $this->postJson(
+        // S2c D4 three-step flow: create draft, save values, submit.
+        $create = $this->postJson(
             "/api/v1/public/forms/{$this->schema->public_token}/submissions",
             [
-                'values' => ['name' => 'Bart'],
+                'idempotency_key' => 'public-rsvp-test-001',
                 'public_submitter_name' => 'Bart',
                 'public_submitter_email' => 'bart@example.nl',
             ],
         );
+        $create->assertCreated();
+        $this->assertSame('draft', $create->json('data.status'));
+        $submissionId = $create->json('data.id');
 
-        $response->assertCreated();
-        $this->assertSame('submitted', $response->json('data.status'));
+        $this->putJson(
+            "/api/v1/public/forms/{$this->schema->public_token}/submissions/{$submissionId}",
+            ['values' => ['name' => 'Bart']],
+        )->assertOk();
+
+        $this->postJson(
+            "/api/v1/public/forms/{$this->schema->public_token}/submissions/{$submissionId}/submit",
+            [],
+        )
+            ->assertCreated()
+            ->assertJsonPath('data.status', 'submitted');
     }
 
     public function test_submit_with_expired_previous_token_returns_410(): void