feat(form-builder): FormBindingApplicator + BindingActivityLogger (WS-6)

Orchestrates per-purpose subject resolution + binding conflict
resolution + per-binding writes per RFC Q4/Q7/Q9. Per-binding failures
captured in BindingPassResult, not thrown — partial failures are
expected and recoverable. Catastrophic failures (no transaction,
unknown purpose, missing schema) throw FormBindingApplicatorException
and bubble.

Per-strategy null-winner matrix implemented via a NO_OP sentinel:
overwrite=write null, append=noop, replace=conditional, first_write_wins=
write only into null target. Append is collection-only with set-merge
semantics (deduplicated array_merge).

Identity-key bindings are skipped during apply — the subject resolver
already used them for lookup/provisioning; re-writing is a no-op or a
clobber.

Activity log hierarchical: one bindings_pass_completed parent +
N binding_applied children with parent_activity_id linkage (RFC Q12).
Failed bindings get error_class/error_message in their activity entry
in addition to their FormSubmissionActionFailure row (deliberate
dual source of truth).

Refs: RFC-WS-6.md §3 (Q4, Q7, Q9, Q12)

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

api/app/FormBuilder/Bindings/BindingActivityLogger.php

@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\FormBuilder\Bindings;
+
+use App\Models\FormBuilder\FormSubmission;
+use Spatie\Activitylog\Models\Activity;
+
+/**
+ * RFC-WS-6 §3 (Q12) — hierarchical activity log for the binding
+ * pipeline. One pass-level activity (form_submission.bindings_pass_completed)
+ * with N child activities (form_submission.binding_applied), linked via
+ * properties.parent_activity_id.
+ *
+ * Failed bindings get their own binding_applied activity entry too,
+ * with `error_class` / `error_message` in properties — in addition to
+ * their FormSubmissionActionFailure row (deliberate dual source of
+ * truth: activity_log is the human timeline, action_failures is the
+ * machine-replayable workflow).
+ */
+final class BindingActivityLogger
+{
+    public function logPass(FormSubmission $submission, BindingPassResult $result): void
+    {
+        $passActivity = activity()
+            ->performedOn($submission)
+            ->withProperties([
+                'binding_count' => count($result->applications),
+                'succeeded' => $result->successCount(),
+                'failed' => $result->failureCount(),
+                'apply_status' => $result->applyStatus()->value,
+                'person_provisioned' => $result->provisionedSubjectType === 'person',
+                'subject_type' => $result->provisionedSubjectType,
+                'subject_id' => $result->provisionedSubjectId,
+            ])
+            ->log('form_submission.bindings_pass_completed');
+
+        $parentActivityId = $passActivity instanceof Activity ? (string) $passActivity->id : null;
+
+        foreach ($result->applications as $application) {
+            $properties = [
+                'parent_activity_id' => $parentActivityId,
+                'binding_id' => $application->bindingId,
+                'target_entity' => $application->targetEntity,
+                'target_attribute' => $application->targetAttribute,
+                'success' => $application->success,
+                'old_value' => $application->oldValue,
+                'new_value' => $application->newValue,
+                'source_submission_id' => (string) $submission->id,
+            ];
+            if (! $application->success) {
+                $properties['error_class'] = $application->exceptionClass;
+                $properties['error_message'] = $application->exceptionMessage;
+            }
+
+            activity()
+                ->performedOn($submission)
+                ->withProperties($properties)
+                ->log('form_submission.binding_applied');
+        }
+    }
+}