diff --git a/scripts/conformance/child-workflows-runtime-probe.php b/scripts/conformance/child-workflows-runtime-probe.php
index 1d68a312..775d48b1 100644
--- a/scripts/conformance/child-workflows-runtime-probe.php
+++ b/scripts/conformance/child-workflows-runtime-probe.php
@@ -267,10 +267,21 @@ function cw_require_child_event(array $history, string $eventType, string $child
     throw new RuntimeException(sprintf('%s did not reference child run %s', $eventType, $childRunId));
 }
 
+/** @return array<string, array{supported: bool, minimum_protocol_version: string, reason: string}> */
+function cw_capability_manifest(): array
+{
+    return array_fill_keys(WorkerProtocol::PORTABLE_WORKER_AFFINITY_CAPABILITIES, [
+        'supported' => false,
+        'minimum_protocol_version' => WorkerProtocol::PORTABLE_WORKER_AFFINITY_MINIMUM_PROTOCOL_VERSION,
+        'reason' => 'not_implemented',
+    ]);
+}
+
 /** @param list<string> $types */
 function cw_register(string $workerId, string $queue, string $runtime, array $types): void
 {
     cw_request('POST', '/worker/register', [
+        'capability_manifest' => cw_capability_manifest(),
         'worker_id' => $workerId,
         'task_queue' => $queue,
         'runtime' => $runtime === 'workflow-php' ? 'php' : 'python',
diff --git a/tests/Unit/ChildWorkflowRuntimeContractTest.php b/tests/Unit/ChildWorkflowRuntimeContractTest.php
index ffd75956..a4db1124 100644
--- a/tests/Unit/ChildWorkflowRuntimeContractTest.php
+++ b/tests/Unit/ChildWorkflowRuntimeContractTest.php
@@ -355,6 +355,14 @@ public function test_published_artifact_runner_routes_every_unexecuted_child_wor
         $this->assertStringContainsString('output_sample', $installProbe);
         $this->assertStringContainsString('WorkflowFiberRunner::forClass(', $runtimeProbe);
         $this->assertStringContainsString('cw_failure_cell(', $runtimeProbe);
+        $this->assertStringContainsString(
+            "'capability_manifest' => cw_capability_manifest(),",
+            $runtimeProbe,
+        );
+        $this->assertStringContainsString(
+            'WorkerProtocol::PORTABLE_WORKER_AFFINITY_CAPABILITIES',
+            $runtimeProbe,
+        );
         $this->assertStringContainsString(
             '$parentRuntimeResult = $parentResume[\'observation\'][\'runtime_result\'] ?? null;',
             $runtimeProbe,