fix(ocap-kernel): deserialize CapData rejections in queueMessage RPC handler

packages/evm-wallet-experiment/test/integration/peer-wallet.test.ts

@@ -265,11 +265,7 @@ describe.sequential('Peer wallet integration', () => {
         // keys so this should reject, not forward to kernel1.
         await expect(
           kernel2.queueMessage(coordinatorKref2, 'signTransaction', [tx]),
-        ).rejects.toMatchObject({
-          body: expect.stringContaining(
-            'No authority to sign this transaction',
-          ),
-        });
+        ).rejects.toThrow('No authority to sign this transaction');
       },
       NETWORK_TIMEOUT,
     );
@@ -284,9 +280,7 @@ describe.sequential('Peer wallet integration', () => {
           kernel2.queueMessage(coordinatorKref2, 'signMessage', [
             'should fail',
           ]),
-        ).rejects.toMatchObject({
-          body: expect.stringContaining('No authority to sign message'),
-        });
+        ).rejects.toThrow('No authority to sign message');
       },
       NETWORK_TIMEOUT,
     );

packages/kernel-node-runtime/test/e2e/libp2p-v3-features.test.ts

@@ -241,11 +241,7 @@ describe.sequential('libp2p v3 Features E2E', () => {
             'hello',
             ['Alice'],
           ]),
-        ).rejects.toMatchObject({
-          body: expect.stringContaining(
-            'Message delivery failed after intentional close',
-          ),
-        });
+        ).rejects.toThrow('Message delivery failed after intentional close');
         const elapsed = Date.now() - start;
 
         // Should fail well under the write timeout

packages/kernel-node-runtime/test/e2e/orphaned-ephemeral-exo.test.ts

@@ -58,9 +58,7 @@ describe('Orphaned ephemeral exo', { timeout: 30_000 }, () => {
         // This is surfaced to the caller as an OBJECT_DELETED kernel error.
         await expect(
           kernel.queueMessage(rootKref, 'useEphemeral', []),
-        ).rejects.toMatchObject({
-          body: expect.stringContaining('[KERNEL:OBJECT_DELETED]'),
-        });
+        ).rejects.toThrow('[KERNEL:OBJECT_DELETED]');
       } finally {
         await kernel.stop();
       }

packages/kernel-node-runtime/test/e2e/remote-comms.test.ts

@@ -825,11 +825,9 @@ describe.sequential('Remote Communications E2E', () => {
         kernel2 = restartResult.kernel;
 
         // The message should not have been delivered because we didn't reconnect
-        await expect(messageAfterClose).rejects.toMatchObject({
-          body: expect.stringContaining(
-            'Message delivery failed after intentional close',
-          ),
-        });
+        await expect(messageAfterClose).rejects.toThrow(
+          'Message delivery failed after intentional close',
+        );
       },
       NETWORK_TIMEOUT * 2,
     );
@@ -916,11 +914,7 @@ describe.sequential('Remote Communications E2E', () => {
             'hello',
             ['Alice'],
           ]),
-        ).rejects.toMatchObject({
-          body: expect.stringContaining(
-            'Message delivery failed after intentional close',
-          ),
-        });
+        ).rejects.toThrow('Message delivery failed after intentional close');
 
         // Manually reconnect
         await kernel1.reconnectPeer(peerId2);
@@ -1009,9 +1003,7 @@ describe.sequential('Remote Communications E2E', () => {
             'hello',
             ['Alice'],
           ]),
-        ).rejects.toMatchObject({
-          body: expect.stringMatching(/Remote connection lost/u),
-        });
+        ).rejects.toThrow(/Remote connection lost/u);
       },
       NETWORK_TIMEOUT * 3,
     );
@@ -1064,9 +1056,7 @@ describe.sequential('Remote Communications E2E', () => {
             'hello',
             ['Alice'],
           ]),
-        ).rejects.toMatchObject({
-          body: expect.stringContaining('Remote connection lost'),
-        });
+        ).rejects.toThrow('Remote connection lost');
       },
       NETWORK_TIMEOUT * 2,
     );

packages/kernel-test/src/endowments.test.ts

@@ -51,9 +51,7 @@ describe('endowments', () => {
 
     await expect(
       kernel.queueMessage(v1Root, 'hello', [`https://${badHost}`]),
-    ).rejects.toMatchObject({
-      body: expect.stringContaining(`Invalid host: ${badHost}`),
-    });
+    ).rejects.toThrow(`Invalid host: ${badHost}`);
 
     await waitUntilQuiescent();
 

packages/kernel-test/src/orphaned-ephemeral-exo.test.ts

@@ -43,8 +43,6 @@ describe('orphaned ephemeral exo', () => {
     // crank, but the endpoint is gone — so it splats and rejects.
     await expect(
       kernel.queueMessage(rootKref, 'useEphemeral', []),
-    ).rejects.toMatchObject({
-      body: expect.stringContaining('[KERNEL:OBJECT_DELETED]'),
-    });
+    ).rejects.toThrow('[KERNEL:OBJECT_DELETED]');
   });
 });

packages/kernel-test/src/syscall-validation.test.ts

@@ -97,9 +97,7 @@ describe('Syscall Validation & Revoked Objects', { timeout: 30_000 }, () => {
     // Try to send message to revoked object — kernel rejects the promise
     await expect(
       kernel.queueMessage(objectKRef, 'getValue', []),
-    ).rejects.toMatchObject({
-      body: expect.stringContaining('[KERNEL:OBJECT_REVOKED]'),
-    });
+    ).rejects.toThrow('[KERNEL:OBJECT_REVOKED]');
     // Verify kernel doesn't crash and exporter vat remains operational
     const exporterStatus = await kernel.queueMessage(exporterKRef, 'noop', []);
     expect(exporterStatus.body).toContain('noop');
@@ -145,19 +143,15 @@ describe('Syscall Validation & Revoked Objects', { timeout: 30_000 }, () => {
     // Send message to revoked object — kernel rejects the promise
     await expect(
       kernel.queueMessage(objectKRef, 'getValue', []),
-    ).rejects.toMatchObject({
-      body: expect.stringContaining('[KERNEL:OBJECT_REVOKED]'),
-    });
+    ).rejects.toThrow('[KERNEL:OBJECT_REVOKED]');
     // Verify exporter vat is still operational
     const exporterStatus = await kernel.queueMessage(exporterKRef, 'noop', []);
     expect(exporterStatus.body).toContain('noop');
     // Verify kernel can handle multiple revoked object accesses
     for (let i = 0; i < 5; i++) {
       await expect(
         kernel.queueMessage(objectKRef, 'getValue', []),
-      ).rejects.toMatchObject({
-        body: expect.stringContaining('[KERNEL:OBJECT_REVOKED]'),
-      });
+      ).rejects.toThrow('[KERNEL:OBJECT_REVOKED]');
     }
     // Verify kernel remains stable
     const finalStatus = await kernel.queueMessage(exporterKRef, 'noop', []);
@@ -217,9 +211,7 @@ describe('Syscall Validation & Revoked Objects', { timeout: 30_000 }, () => {
     for (const objectKRef of objectKRefs) {
       await expect(
         kernel.queueMessage(objectKRef, 'getValue', []),
-      ).rejects.toMatchObject({
-        body: expect.stringContaining('[KERNEL:OBJECT_REVOKED]'),
-      });
+      ).rejects.toThrow('[KERNEL:OBJECT_REVOKED]');
     }
 
     // Verify exporter vat is still operational

packages/kernel-test/src/vat-lifecycle.test.ts

@@ -134,9 +134,7 @@ describe('Vat Lifecycle', { timeout: 30_000 }, () => {
     // Try to send a message to the terminated vat's root object — rejects
     await expect(
       kernel.queueMessage(deadRootObject, 'resume', []),
-    ).rejects.toMatchObject({
-      body: expect.stringContaining('[KERNEL:OBJECT_DELETED]'),
-    });
+    ).rejects.toThrow('[KERNEL:OBJECT_DELETED]');
 
     // Verify that messaging works as expected
     expect(await runResume(kernel, liveRootObject)).toBe(

packages/ocap-kernel/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Deserialize CapData rejections in `Kernel.queueMessage` so vat errors surface as plain `Error` objects to all callers ([#928](https://github.com/MetaMask/ocap-kernel/pull/928))
+
 ## [0.7.0]
 
 ### Added

packages/ocap-kernel/src/Kernel.test.ts

@@ -7,6 +7,7 @@ import type { Mocked, MockInstance } from 'vitest';
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 
 import { Kernel } from './Kernel.ts';
+import { kser } from './liveslots/kernel-marshal.ts';
 import type {
   VatId,
   VatConfig,
@@ -214,6 +215,33 @@ describe('Kernel', () => {
       const result = await kernel.queueMessage('ko1', 'hello', []);
       expect(result).toStrictEqual({ body: '{"result":"ok"}', slots: [] });
     });
+
+    it('deserializes CapData rejections into Errors', async () => {
+      const kernel = await Kernel.make(
+        mockPlatformServices,
+        mockKernelDatabase,
+      );
+      mocks.KernelQueue.lastInstance.enqueueMessage.mockRejectedValueOnce(
+        kser(new Error('vat rejection message')),
+      );
+      await expect(kernel.queueMessage('ko1', 'hello', [])).rejects.toThrow(
+        'vat rejection message',
+      );
+    });
+
+    it('propagates non-CapData rejections as-is', async () => {
+      const kernel = await Kernel.make(
+        mockPlatformServices,
+        mockKernelDatabase,
+      );
+      const internalError = new Error('internal kernel error');
+      mocks.KernelQueue.lastInstance.enqueueMessage.mockRejectedValueOnce(
+        internalError,
+      );
+      await expect(kernel.queueMessage('ko1', 'hello', [])).rejects.toThrow(
+        'internal kernel error',
+      );
+    });
   });
 
   describe('launchSubcluster()', () => {

packages/ocap-kernel/src/Kernel.ts

@@ -1,5 +1,6 @@
 import type { CapData } from '@endo/marshal';
 import type { KernelDatabase } from '@metamask/kernel-store';
+import { isCapData } from '@metamask/kernel-utils';
 import { Logger } from '@metamask/logger';
 
 import { IOManager } from './io/IOManager.ts';
@@ -10,8 +11,8 @@ import { KernelQueue } from './KernelQueue.ts';
 import { KernelRouter } from './KernelRouter.ts';
 import { KernelServiceManager } from './KernelServiceManager.ts';
 import type { KernelService } from './KernelServiceManager.ts';
+import { kslot, kunser } from './liveslots/kernel-marshal.ts';
 import type { SlotValue } from './liveslots/kernel-marshal.ts';
-import { kslot } from './liveslots/kernel-marshal.ts';
 import { OcapURLManager } from './remotes/kernel/OcapURLManager.ts';
 import { RemoteManager } from './remotes/kernel/RemoteManager.ts';
 import type { RemoteCommsOptions } from './remotes/types.ts';
@@ -386,7 +387,14 @@ export class Kernel {
     method: string,
     args: unknown[],
   ): Promise<CapData<KRef>> {
-    return this.#kernelQueue.enqueueMessage(target, method, args);
+    try {
+      return await this.#kernelQueue.enqueueMessage(target, method, args);
+    } catch (rejection) {
+      if (isCapData(rejection)) {
+        throw kunser(rejection as CapData<KRef>);
+      }
+      throw rejection;
+    }
   }
 
   /**

packages/ocap-kernel/src/rpc/kernel-control/queue-message.test.ts

@@ -64,7 +64,7 @@ describe('queueMessageHandler', () => {
     expect(result).toStrictEqual(expectedResult);
   });
 
-  it('should propagate errors from kernel.queueMessage', async () => {
+  it('propagates rejections from kernel.queueMessage', async () => {
     const error = new Error('Queue message failed');
     vi.mocked(mockKernel.queueMessage).mockRejectedValueOnce(error);
 

packages/ocap-kernel/src/vats/SubclusterManager.ts

@@ -1,6 +1,5 @@
 import type { CapData } from '@endo/marshal';
 import { SubclusterNotFoundError } from '@metamask/kernel-errors';
-import { isCapData } from '@metamask/kernel-utils';
 import { Logger } from '@metamask/logger';
 
 import type { IOManager } from '../io/IOManager.ts';
@@ -341,22 +340,10 @@ export class SubclusterManager {
         `Bootstrap vat "${config.bootstrap}" not found in rootIds`,
       );
     }
-    let bootstrapResult: CapData<KRef>;
-    try {
-      bootstrapResult = await this.#queueMessage(rootKref, 'bootstrap', [
-        roots,
-        services,
-      ]);
-    } catch (rejection) {
-      // queueMessage rejects with CapData for rejected kernel promises.
-      // Deserialize to surface the original Error to the caller.
-      // If the rejection isn't CapData (e.g., an internal error before the
-      // kernel promise was created), re-throw as-is.
-      if (isCapData(rejection)) {
-        throw kunser(rejection as CapData<KRef>);
-      }
-      throw rejection;
-    }
+    const bootstrapResult = await this.#queueMessage(rootKref, 'bootstrap', [
+      roots,
+      services,
+    ]);
     const unserialized = kunser(bootstrapResult);
     if (unserialized instanceof Error) {
       throw unserialized;