diff --git a/packages/workflow-executor/src/adapters/forestadmin-client-activity-log-port.ts b/packages/workflow-executor/src/adapters/forestadmin-client-activity-log-port.ts
index 07e0dcf97c..783cd63a19 100644
--- a/packages/workflow-executor/src/adapters/forestadmin-client-activity-log-port.ts
+++ b/packages/workflow-executor/src/adapters/forestadmin-client-activity-log-port.ts
@@ -40,6 +40,17 @@ export default class ForestadminClientActivityLogPort implements ActivityLogPort
         { logger: this.logger },
       );
 
+      // Observed: server replies 200 with a null id when it declines to persist (PRD-428).
+      // Surface it once here; later mark-as-* calls then no-op instead of 404-looping.
+      if (!response.id) {
+        this.logger.warn('activity log not persisted by server — status updates will be skipped', {
+          action: args.action,
+          collectionId: args.collectionId,
+        });
+
+        return { id: null };
+      }
+
       return { id: response.id, index: response.attributes.index };
     } catch (cause) {
       this.logger.error('activity log create failed', {
@@ -53,6 +64,11 @@ export default class ForestadminClientActivityLogPort implements ActivityLogPort
   }
 
   async markSucceeded(handle: ActivityLogHandle): Promise<void> {
+    // Not persisted (see createPending) → no log to update; skip the 404-retrying status call.
+    if (!('index' in handle)) return undefined;
+
+    const { id, index } = handle;
+
     return this.drainer.track(async () => {
       try {
         await withRetry(
@@ -60,14 +76,14 @@ export default class ForestadminClientActivityLogPort implements ActivityLogPort
           () =>
             this.service.updateActivityLogStatus({
               forestServerToken: this.forestServerToken,
-              activityLog: { id: handle.id, attributes: { index: handle.index } },
+              activityLog: { id, attributes: { index } },
               status: 'completed',
             }),
           { logger: this.logger, extraRetryStatuses: [404] },
         );
       } catch (err) {
         this.logger.error('activity log mark-as-completed failed', {
-          handleId: handle.id,
+          handleId: id,
           error: extractErrorMessage(err),
         });
       }
@@ -75,6 +91,11 @@ export default class ForestadminClientActivityLogPort implements ActivityLogPort
   }
 
   async markFailed(handle: ActivityLogHandle, errorMessage: string): Promise<void> {
+    // Not persisted (see markSucceeded) → skip.
+    if (!('index' in handle)) return undefined;
+
+    const { id, index } = handle;
+
     return this.drainer.track(async () => {
       try {
         await withRetry(
@@ -82,14 +103,14 @@ export default class ForestadminClientActivityLogPort implements ActivityLogPort
           () =>
             this.service.updateActivityLogStatus({
               forestServerToken: this.forestServerToken,
-              activityLog: { id: handle.id, attributes: { index: handle.index } },
+              activityLog: { id, attributes: { index } },
               status: 'failed',
             }),
           { logger: this.logger, extraRetryStatuses: [404] },
         );
       } catch (err) {
         this.logger.error('activity log mark-as-failed failed', {
-          handleId: handle.id,
+          handleId: id,
           stepErrorMessage: errorMessage,
           error: extractErrorMessage(err),
         });
diff --git a/packages/workflow-executor/src/ports/activity-log-port.ts b/packages/workflow-executor/src/ports/activity-log-port.ts
index 15ce3f4801..c1843ff8ca 100644
--- a/packages/workflow-executor/src/ports/activity-log-port.ts
+++ b/packages/workflow-executor/src/ports/activity-log-port.ts
@@ -7,10 +7,9 @@ export interface CreateActivityLogArgs {
   label?: string;
 }
 
-export interface ActivityLogHandle {
-  id: string;
-  index: string;
-}
+// `{ id: null }` means the server declined to persist the log (returns 200 with a null id).
+// markSucceeded/markFailed short-circuit on it — there is nothing to update.
+export type ActivityLogHandle = { id: string; index: string } | { id: null };
 
 // Per-run scoped port: token baked into the adapter's constructor. markSucceeded/markFailed
 // retry transient failures internally and are invoked with `void` from base-step-executor.
diff --git a/packages/workflow-executor/test/adapters/forestadmin-client-activity-log-port.test.ts b/packages/workflow-executor/test/adapters/forestadmin-client-activity-log-port.test.ts
index 1614b330ab..680f5d7948 100644
--- a/packages/workflow-executor/test/adapters/forestadmin-client-activity-log-port.test.ts
+++ b/packages/workflow-executor/test/adapters/forestadmin-client-activity-log-port.test.ts
@@ -166,9 +166,45 @@ describe('ForestadminClientActivityLogPort', () => {
         expect.objectContaining({ collectionName: '11' }),
       );
     });
+
+    it('warns (with collectionId) and returns a not-persisted handle when the server responds 200 with id:null', async () => {
+      const service = makeService();
+      service.createActivityLog.mockResolvedValue({
+        id: null,
+        attributes: {},
+      } as unknown as { id: string; attributes: { index: string } });
+      const logger = makeLogger();
+      const port = makePort(service, { logger });
+
+      const handle = await port.createPending({
+        renderingId: 5,
+        action: 'action',
+        type: 'write',
+        collectionId: '11',
+      });
+
+      expect(handle).toEqual({ id: null });
+      expect(service.createActivityLog).toHaveBeenCalledTimes(1);
+      expect(logger.warn).toHaveBeenCalledWith(
+        'activity log not persisted by server — status updates will be skipped',
+        { action: 'action', collectionId: '11' },
+      );
+    });
   });
 
   describe('markSucceeded', () => {
+    it('skips the status update and drainer tracking when the handle was not persisted', async () => {
+      const service = makeService();
+      const drainer = new ActivityLogDrainer();
+      const trackSpy = jest.spyOn(drainer, 'track');
+      const port = makePort(service, { drainer });
+
+      await port.markSucceeded({ id: null });
+
+      expect(service.updateActivityLogStatus).not.toHaveBeenCalled();
+      expect(trackSpy).not.toHaveBeenCalled();
+    });
+
     it('retries on 503 and eventually resolves without rethrowing', async () => {
       const service = makeService();
       service.updateActivityLogStatus
@@ -214,6 +250,18 @@ describe('ForestadminClientActivityLogPort', () => {
   });
 
   describe('markFailed', () => {
+    it('skips the status update and drainer tracking when the handle was not persisted', async () => {
+      const service = makeService();
+      const drainer = new ActivityLogDrainer();
+      const trackSpy = jest.spyOn(drainer, 'track');
+      const port = makePort(service, { drainer });
+
+      await port.markFailed({ id: null }, 'boom');
+
+      expect(service.updateActivityLogStatus).not.toHaveBeenCalled();
+      expect(trackSpy).not.toHaveBeenCalled();
+    });
+
     it('sends status: failed (no errorMessage — server schema rejects unknown fields) and retries on 503', async () => {
       const service = makeService();
       service.updateActivityLogStatus