diff --git a/packages/workflow-executor/src/adapters/server-types.ts b/packages/workflow-executor/src/adapters/server-types.ts
index e897f3012e..10382882fd 100644
--- a/packages/workflow-executor/src/adapters/server-types.ts
+++ b/packages/workflow-executor/src/adapters/server-types.ts
@@ -39,8 +39,9 @@ export enum ServerStepExecutionTypeEnum {
 
 interface ServerWorkflowStepBase {
   type: ServerStepTypeEnum;
-  title: string;
-  prompt?: string;
+  // The orchestrator serializes missing BPMN attributes as null (DOM getAttribute), never omits.
+  title: string | null;
+  prompt?: string | null;
   executionType: ServerStepExecutionTypeEnum;
   automaticCompletion: boolean;
   outgoing: ServerWorkflowTransition[];
@@ -50,7 +51,7 @@ export interface ServerWorkflowTaskBase extends ServerWorkflowStepBase {
   type: ServerStepTypeEnum.Task;
   taskType: ServerTaskTypeEnum;
   isSubTask?: boolean;
-  prompt: string;
+  prompt: string | null;
   outgoing: [ServerWorkflowTransition];
 }
 
diff --git a/packages/workflow-executor/src/types/validated/step-definition.ts b/packages/workflow-executor/src/types/validated/step-definition.ts
index a074778b43..159b5df947 100644
--- a/packages/workflow-executor/src/types/validated/step-definition.ts
+++ b/packages/workflow-executor/src/types/validated/step-definition.ts
@@ -23,10 +23,17 @@ export enum StepExecutionMode {
 // Shared fields across all step types. executionType is intentionally excluded —
 // each schema declares its own valid modes (most with .default().catch() for normalization;
 // guidance deliberately omits .catch to fail loud on an unknown mode).
+// The orchestrator serializes missing BPMN attributes as JSON null (DOM getAttribute), not as
+// absent keys — accept both and normalize to undefined.
+const optionalString = z
+  .string()
+  .nullish()
+  .transform(value => value ?? undefined);
+
 const sharedFields = {
-  prompt: z.string().optional(),
-  aiConfigName: z.string().optional(),
-  title: z.string().optional(),
+  prompt: optionalString,
+  aiConfigName: optionalString,
+  title: optionalString,
 };
 
 // Use z.enum(EnumObject), not z.nativeEnum — the latter is deprecated in zod 4.
diff --git a/packages/workflow-executor/test/adapters/step-definition-mapper.test.ts b/packages/workflow-executor/test/adapters/step-definition-mapper.test.ts
index e64cc8073d..d8d11d68b5 100644
--- a/packages/workflow-executor/test/adapters/step-definition-mapper.test.ts
+++ b/packages/workflow-executor/test/adapters/step-definition-mapper.test.ts
@@ -309,6 +309,38 @@ describe('toStepDefinition', () => {
         options: ['Valid', 'AlsoValid'],
       });
     });
+
+    it('accepts a condition whose title and prompt are null (unnamed BPMN gateway)', () => {
+      const condition = makeCondition(
+        [
+          { stepId: 's1', buttonText: 'Option A' },
+          { stepId: 's2', buttonText: 'Option B' },
+        ],
+        { title: null, prompt: null },
+      );
+
+      expect(toStepDefinition(condition)).toMatchObject({
+        type: 'condition',
+        title: undefined,
+        prompt: undefined,
+        options: ['Option A', 'Option B'],
+      });
+    });
+  });
+
+  describe('null shared fields', () => {
+    it('accepts a task whose title and prompt are null (serialized missing BPMN attributes)', () => {
+      const task = makeTask({
+        title: null,
+        prompt: null,
+      });
+
+      expect(toStepDefinition(task)).toMatchObject({
+        type: 'read-record',
+        title: undefined,
+        prompt: undefined,
+      });
+    });
   });
 
   describe('unsupported step types', () => {