diff --git a/packages/acp/acp/src/index.ts b/packages/acp/acp/src/index.ts
index 7af26b594a..b88322012c 100644
--- a/packages/acp/acp/src/index.ts
+++ b/packages/acp/acp/src/index.ts
@@ -14,7 +14,7 @@ import { randomUUID } from 'node:crypto'
 import { isAbsolute } from 'node:path'
 import { Readable, Writable } from 'node:stream'
 import Schema from 'schemastery'
-import { createUserMessage } from '@deepseek-ai/dsh-llm'
+import { createUserMessage, errorChain } from '@deepseek-ai/dsh-llm'
 import {
   AgentSideConnection,
   ndJsonStream,
@@ -368,11 +368,10 @@ export function apply(ctx: Context, config: AcpConfig): void {
         if (result.status === 'rejected') failures.push(result.reason as unknown)
       }
       if (failures.length > 0) {
-        // The only production consumer logs this error through `String`, which
-        // renders the message alone — without the joined reasons, per-session
-        // disposal failures would vanish from operational logs. Join them like
-        // the subagent seam's own aggregate disposal messages.
-        const detail = failures.map(failure => String(failure)).join('; ')
+        // The production consumer logs this AggregateError through `String`,
+        // which renders only its message. Embed every per-session diagnostic,
+        // including nested causes and aggregate members, in that message.
+        const detail = failures.map(failure => errorChain(failure)).join('; ')
         throw new AggregateError(
           failures,
           `ACP agent teardown failed for ${failures.length} session(s): ${detail}`,
diff --git a/packages/acp/acp/tests/dispose.spec.ts b/packages/acp/acp/tests/dispose.spec.ts
index 0eea014eeb..b4b1eaeef2 100644
--- a/packages/acp/acp/tests/dispose.spec.ts
+++ b/packages/acp/acp/tests/dispose.spec.ts
@@ -96,7 +96,7 @@ describe('ACP connection ownership', () => {
     expect(harness.ctx.agents.get(SessionId(sessionId))).toBeUndefined()
   })
 
-  it('awaits every owned session disposal before reporting one failure', async () => {
+  it('awaits every owned session disposal and reports nested failure reasons', async () => {
     harness = await makeBridgeHarness()
     const create = harness.ctx.agents.create.bind(harness.ctx.agents)
     const releaseSecond = Promise.withResolvers<undefined>()
@@ -110,7 +110,10 @@ describe('ACP connection ownership', () => {
       if (created++ === 0) {
         handle.dispose = async () => {
           await originalDispose()
-          throw new Error('first session cleanup failed')
+          throw new AggregateError([
+            new Error('scope cleanup failed', { cause: new Error('sqlite busy') }),
+            new Error('hook cleanup failed'),
+          ], 'first session cleanup failed')
         }
       } else {
         handle.dispose = async () => {
@@ -132,7 +135,10 @@ describe('ACP connection ownership', () => {
     releaseSecond.resolve(undefined)
     await vi.waitFor(() => {
       expect(warnings.some(warning =>
-        warning.includes('ACP agent teardown failed for 1 session(s): Error: first session cleanup failed'))).toBe(true)
+        warning.includes(
+          'ACP agent teardown failed for 1 session(s): '
+          + 'first session cleanup failed [scope cleanup failed: sqlite busy; hook cleanup failed]',
+        ))).toBe(true)
       expect(harness!.ctx.agents.get(SessionId(first.sessionId))).toBeUndefined()
       expect(harness!.ctx.agents.get(SessionId(second.sessionId))).toBeUndefined()
     })