Always emit failure_category in FailureHandled history events

Closes #26 (TD-007). FailureHandled payloads previously omitted the
failure_category field — downstream consumers had to load the WorkflowFailure
DB row to see what kind of failure was caught. Now the event payload itself
carries the canonical FailureCategory enum value, with fallback ordering:

1. WorkflowFailure model (authoritative; enum-cast) when loaded from DB
2. failurePayload['failure_category'] (used for child-propagated failures
   where the payload is copied from the child's WorkflowFailed event)
3. FailureCategory::Application as catch-all so the field is always present

resolveFailureHandledCategory rejects non-enum values via tryFrom, so
unmappable dev-era strings won't leak through — matching the issue
directive that v2 dev artifacts get dropped, not preserved with shims.

Test coverage extends testWorkflowCanHandleActivityFailureAndContinue to
assert (a) the payload's category matches the WorkflowFailure row and
(b) it's a member of the FailureCategory enum.

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

Author: durable-workflow-ops

src/V2/Support/WorkflowExecutor.php

@@ -2947,10 +2947,12 @@ private function recordFailureHandled(
         $exceptionType = is_string($failurePayload['exception_type'] ?? null)
             ? $failurePayload['exception_type']
             : (is_string($exceptionPayload['type'] ?? null) ? $exceptionPayload['type'] : null);
+        $failureCategory = self::resolveFailureHandledCategory($failure, $failurePayload);
 
         WorkflowHistoryEvent::record($run, HistoryEventType::FailureHandled, array_filter([
             'failure_id' => $failureId,
             'sequence' => $workflowSequence,
+            'failure_category' => $failureCategory,
             'source_kind' => $failure?->source_kind
                 ?? (is_string($failurePayload['source_kind'] ?? null) ? $failurePayload['source_kind'] : null),
             'source_id' => $failure?->source_id
@@ -2968,6 +2970,34 @@ private function recordFailureHandled(
         ], static fn (mixed $value): bool => $value !== null), $task);
     }
 
+    /**
+     * Resolve a canonical FailureCategory value for a FailureHandled event.
+     *
+     * The DB row is authoritative when available (it carries an enum-cast
+     * value); fall back to the failurePayload (which carries the same string
+     * for child propagation), then to the catch-all Application category so
+     * downstream consumers can rely on the field being present and a member
+     * of the FailureCategory enum.
+     *
+     * @param array<string, mixed> $failurePayload
+     */
+    private static function resolveFailureHandledCategory(
+        ?WorkflowFailure $failure,
+        array $failurePayload,
+    ): string {
+        $modelCategory = $failure?->failure_category;
+        if ($modelCategory instanceof FailureCategory) {
+            return $modelCategory->value;
+        }
+
+        $payloadCategory = $failurePayload['failure_category'] ?? null;
+        if (is_string($payloadCategory) && FailureCategory::tryFrom($payloadCategory) !== null) {
+            return $payloadCategory;
+        }
+
+        return FailureCategory::Application->value;
+    }
+
     private function startChildRetryIfAvailable(
         WorkflowRun $parentRun,
         int $sequence,

tests/Feature/V2/V2WorkflowTest.php

@@ -4311,6 +4311,12 @@ public function testWorkflowCanHandleActivityFailureAndContinue(): void
         $this->assertSame('activity_execution', $handledEvent->payload['source_kind'] ?? null);
         $this->assertSame($failure->source_id, $handledEvent->payload['source_id'] ?? null);
         $this->assertSame('activity', $handledEvent->payload['propagation_kind'] ?? null);
+        $this->assertSame($failure->failure_category->value, $handledEvent->payload['failure_category'] ?? null);
+        $this->assertTrue(in_array(
+            $handledEvent->payload['failure_category'] ?? null,
+            array_map(static fn ($c) => $c->value, FailureCategory::cases()),
+            true,
+        ), 'FailureHandled payload must carry a known FailureCategory enum value.');
         $this->assertTrue($handledEvent->payload['handled'] ?? false);
     }