diff --git a/packages/acp/acp/src/content.ts b/packages/acp/acp/src/content.ts
index 56e027a1b7..66ac7ea3be 100644
--- a/packages/acp/acp/src/content.ts
+++ b/packages/acp/acp/src/content.ts
@@ -2,7 +2,7 @@
 
 import type { ContentBlock as AcpContentBlock } from '@agentclientprotocol/sdk'
 import type { Context } from '@deepseek-ai/cordis'
-import { AttachmentError } from '@deepseek-ai/dsh-attachment'
+import { isImageAdmissionError } from '@deepseek-ai/dsh-attachment'
 import type { ImageAttachmentRef, ImageMediaType, SaveImageAttachment } from '@deepseek-ai/dsh-attachment'
 import type { Agent } from '@deepseek-ai/dsh-agent'
 import type { ContentBlock } from '@deepseek-ai/dsh-llm'
@@ -72,7 +72,7 @@ async function assertImageRoute(ctx: Context, agent: Agent, signal: AbortSignal)
   try {
     info = await llm.resolveModelInfo(provider, model, signal)
   } catch (error: unknown) {
-    throw new AcpContentError('the current model route could not be verified for image input', 'invalid', { cause: error })
+    throw new AcpContentError('the current model route could not be verified for image input', 'internal', { cause: error })
   }
   if (info.inputModalities === undefined || !info.inputModalities.includes('image')) {
     throw new AcpContentError(`model "${model}" does not declare image input`, 'invalid')
@@ -157,7 +157,7 @@ export async function admitAcpPrompt(
     try {
       refs = await attachments.saveImages(images)
     } catch (error: unknown) {
-      if (error instanceof AttachmentError && error.code !== 'ATTACHMENT_WRITE_FAILED') {
+      if (isImageAdmissionError(error)) {
         throw new AcpContentError(error.message, 'invalid', { cause: error })
       }
       throw new AcpContentError('unable to persist the prompt image batch', 'internal', { cause: error })
diff --git a/packages/acp/acp/tests/content.spec.ts b/packages/acp/acp/tests/content.spec.ts
index 476708d687..a22dbe9069 100644
--- a/packages/acp/acp/tests/content.spec.ts
+++ b/packages/acp/acp/tests/content.spec.ts
@@ -133,8 +133,9 @@ describe('ACP rich content codec', () => {
 
     const broken = admissionFixture()
     broken.resolveModelInfo.mockRejectedValueOnce(new Error('catalog down'))
-    await expect(admitAcpPrompt(broken.ctx, broken.agent, prompt, true, new AbortController().signal))
-      .rejects.toThrow(/route could not be verified/)
+    const routeFailure = admitAcpPrompt(broken.ctx, broken.agent, prompt, true, new AbortController().signal)
+    await expect(routeFailure).rejects.toMatchObject({ kind: 'internal' })
+    await expect(routeFailure).rejects.toThrow(/route could not be verified/)
     const unknown = admissionFixture()
     unknown.resolveModelInfo.mockResolvedValueOnce({ provider: 'mock', id: 'vision', name: 'vision' })
     await expect(admitAcpPrompt(unknown.ctx, unknown.agent, prompt, true, new AbortController().signal))
@@ -158,6 +159,9 @@ describe('ACP rich content codec', () => {
     await expect(admitAcpPrompt(fixture.ctx, fixture.agent, prompt, true, new AbortController().signal))
       .rejects.toMatchObject({ kind: 'invalid', message: 'too many' })
     fixture.saveImages.mockRejectedValueOnce(new AttachmentError('disk failed', 'ATTACHMENT_WRITE_FAILED'))
+    await expect(admitAcpPrompt(fixture.ctx, fixture.agent, prompt, true, new AbortController().signal))
+      .rejects.toMatchObject({ kind: 'internal', message: 'unable to persist the prompt image batch' })
+    fixture.saveImages.mockRejectedValueOnce(new AttachmentError('corrupt object', 'ATTACHMENT_CORRUPT'))
     await expect(admitAcpPrompt(fixture.ctx, fixture.agent, prompt, true, new AbortController().signal))
       .rejects.toMatchObject({ kind: 'internal', message: 'unable to persist the prompt image batch' })
     fixture.saveImages.mockRejectedValueOnce(new Error('unknown store failure'))
diff --git a/packages/attachment/attachment/README.i18n.yaml b/packages/attachment/attachment/README.i18n.yaml
index cef3af3a62..b88b6b2132 100644
--- a/packages/attachment/attachment/README.i18n.yaml
+++ b/packages/attachment/attachment/README.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/attachment/attachment/README.md
-README.md: c0a86d324da8c27ec386103f40ac50534c2483d7
-README.zh.md: 562c8af0df20634ac2072c4a8d422b4e0b4b47dd
+README.md: 05c4bce5498f3c0bf172264be3e4b834ea0925e2
+README.zh.md: 91a454da09d32b0a87d02ca7ccb482e95c485a37
diff --git a/packages/attachment/attachment/README.md b/packages/attachment/attachment/README.md
index c0a86d324d..05c4bce549 100644
--- a/packages/attachment/attachment/README.md
+++ b/packages/attachment/attachment/README.md
@@ -4,7 +4,7 @@ English | [中文](README.zh.md)
 
 The durable attachment seam. `ctx.attachments` validates and durably commits immutable image bytes, then returns a serializable `ImageAttachmentRef`; consumers never persist browser paths, object URLs, provider URLs, or base64 in session events.
 
-Unsent composer images remain browser-owned temporary drafts. `validateImage` runs the same admission policy without persisting. `saveImages` owns batch count and aggregate-byte limits, validates every member before writing any member, then commits in order and returns references only after the complete batch succeeds. A later storage failure returns no partial references, although an earlier immutable content-addressed object may remain unreachable until reference-aware garbage collection exists. `saveImage` commits one accepted image before any model-visible session event is published, and `readImage` verifies the content-addressed object against its logged metadata. Callers may cancel `readImage`; implementations observe cancellation around backend and verification work and preserve it instead of translating it into a storage failure.
+Unsent composer images remain browser-owned temporary drafts. `validateImage` runs the same admission policy without persisting. `saveImages` owns batch count and aggregate-byte limits, validates every member before writing any member, then commits in order and returns references only after the complete batch succeeds. A later storage failure returns no partial references, although an earlier immutable content-addressed object may remain unreachable until reference-aware garbage collection exists. `isImageAdmissionError` distinguishes caller-correctable image-policy failures from storage faults so each protocol adapter can map its own error vocabulary. `saveImage` commits one accepted image before any model-visible session event is published, and `readImage` verifies the content-addressed object against its logged metadata. Callers may cancel `readImage`; implementations observe cancellation around backend and verification work and preserve it instead of translating it into a storage failure.
 
 ## Model Experience
 
diff --git a/packages/attachment/attachment/README.zh.md b/packages/attachment/attachment/README.zh.md
index 562c8af0df..91a454da09 100644
--- a/packages/attachment/attachment/README.zh.md
+++ b/packages/attachment/attachment/README.zh.md
@@ -4,7 +4,7 @@
 
 持久附件服务边界。`ctx.attachments` 校验并持久提交不可变图片字节，随后返回可序列化的 `ImageAttachmentRef`；消费方绝不会在会话事件中持久保存浏览器路径、对象 URL、提供方 URL 或 base64。
 
-未发送的输入区图片仍是由浏览器持有的临时草稿。`validateImage` 运行相同的准入策略，但不执行持久化。`saveImages` 负责批次图片数量和总字节限制，先校验全部成员，再按顺序提交，并且只在完整批次成功后返回引用。后续存储失败不会返回部分引用，但较早写入的不可变内容寻址对象可能保持不可达，直至具备按引用感知的垃圾回收。`saveImage` 会在发布任何模型可见的会话事件前提交一张已接受的图片，`readImage` 则根据已记录的元数据校验内容寻址对象。调用方可以取消 `readImage`；实现会在后端读取与校验工作的边界观察取消，并保留取消语义，而不会将其转换为存储失败。
+未发送的输入区图片仍是由浏览器持有的临时草稿。`validateImage` 运行相同的准入策略，但不执行持久化。`saveImages` 负责批次图片数量和总字节限制，先校验全部成员，再按顺序提交，并且只在完整批次成功后返回引用。后续存储失败不会返回部分引用，但较早写入的不可变内容寻址对象可能保持不可达，直至具备按引用感知的垃圾回收。`isImageAdmissionError` 区分可由调用方修正的图片策略失败与存储故障，使每个协议适配器可以映射自己的错误词汇。`saveImage` 会在发布任何模型可见的会话事件前提交一张已接受的图片，`readImage` 则根据已记录的元数据校验内容寻址对象。调用方可以取消 `readImage`；实现会在后端读取与校验工作的边界观察取消，并保留取消语义，而不会将其转换为存储失败。
 
 ## 模型体验
 
diff --git a/packages/attachment/attachment/src/error.ts b/packages/attachment/attachment/src/error.ts
index 827d77f58a..071d2bc39b 100644
--- a/packages/attachment/attachment/src/error.ts
+++ b/packages/attachment/attachment/src/error.ts
@@ -24,3 +24,26 @@ export class AttachmentError extends Error {
     this.code = code
   }
 }
+
+/** Attachment failures caused by the caller's proposed image batch. */
+const IMAGE_ADMISSION_ERROR_CODES = new Set([
+  'TOO_MANY_IMAGES',
+  'IMAGES_TOO_LARGE',
+  'UNSUPPORTED_IMAGE_TYPE',
+  'INVALID_IMAGE',
+  'IMAGE_TYPE_MISMATCH',
+  'IMAGE_TOO_LARGE',
+  'IMAGE_TOO_MANY_PIXELS',
+])
+
+/**
+ * Distinguish caller-correctable image admission failures from storage faults.
+ * @param error - failure raised while validating or persisting an image batch.
+ * @returns whether the caller can correct the proposed image content or batch.
+ */
+export function isImageAdmissionError(error: unknown): error is AttachmentError {
+  return error instanceof Error
+    && 'code' in error
+    && typeof error.code === 'string'
+    && IMAGE_ADMISSION_ERROR_CODES.has(error.code)
+}
diff --git a/packages/attachment/attachment/src/index.ts b/packages/attachment/attachment/src/index.ts
index 72e680f010..8c411dbfa5 100644
--- a/packages/attachment/attachment/src/index.ts
+++ b/packages/attachment/attachment/src/index.ts
@@ -10,7 +10,7 @@ import type {
 } from './types.ts'
 
 export { AttachmentId } from './brand.ts'
-export { AttachmentError } from './error.ts'
+export { AttachmentError, isImageAdmissionError } from './error.ts'
 export type {
   AttachmentId as AttachmentIdType,
   ImageAttachmentLimits,
diff --git a/packages/attachment/attachment/tests/index.spec.ts b/packages/attachment/attachment/tests/index.spec.ts
index 5a75c24dc4..18aa6894f2 100644
--- a/packages/attachment/attachment/tests/index.spec.ts
+++ b/packages/attachment/attachment/tests/index.spec.ts
@@ -1,7 +1,9 @@
 import { Context } from '@deepseek-ai/cordis'
 import { describe, expect, it } from 'vitest'
 import AttachmentStore, {
+  AttachmentError,
   AttachmentId,
+  isImageAdmissionError,
   type ImageAttachmentRef,
   type ImageMediaType,
   type SaveImageAttachment,
@@ -93,3 +95,14 @@ describe('AttachmentStore.saveImages', () => {
     expect(store.calls).toEqual(['validate:1', 'validate:2', 'save:1', 'save:2'])
   })
 })
+
+describe('isImageAdmissionError', () => {
+  it('separates caller-correctable image policy failures from storage faults', () => {
+    expect(isImageAdmissionError(new AttachmentError('bad bytes', 'INVALID_IMAGE'))).toBe(true)
+    expect(isImageAdmissionError(new AttachmentError('too many', 'TOO_MANY_IMAGES'))).toBe(true)
+    expect(isImageAdmissionError(Object.assign(new Error('foreign policy error'), { code: 'IMAGE_TOO_LARGE' }))).toBe(true)
+    expect(isImageAdmissionError(new AttachmentError('corrupt object', 'ATTACHMENT_CORRUPT'))).toBe(false)
+    expect(isImageAdmissionError(new AttachmentError('disk failed', 'ATTACHMENT_WRITE_FAILED'))).toBe(false)
+    expect(isImageAdmissionError(new Error('unknown failure'))).toBe(false)
+  })
+})
diff --git a/packages/mcp/mcp-client/src/tools.ts b/packages/mcp/mcp-client/src/tools.ts
index aff1c19175..e5bf7a93a6 100644
--- a/packages/mcp/mcp-client/src/tools.ts
+++ b/packages/mcp/mcp-client/src/tools.ts
@@ -18,6 +18,7 @@ import type { Client } from '@modelcontextprotocol/sdk/client/index.js'
 import { ListToolsResultSchema } from '@modelcontextprotocol/sdk/types.js'
 import { z } from 'zod'
 import type { Context } from '@deepseek-ai/cordis'
+import { isImageAdmissionError } from '@deepseek-ai/dsh-attachment'
 import type { AttachmentStore, ImageAttachmentRef, ImageMediaType, SaveImageAttachment } from '@deepseek-ai/dsh-attachment'
 import type { ContentBlock } from '@deepseek-ai/dsh-llm'
 import type { ToolDefinition, ToolExecution, ToolExecutionResult } from '@deepseek-ai/dsh-tools'
@@ -474,10 +475,13 @@ async function prepareImageProjection(
       type: 'image',
       attachment: byIndex.get(index) as ImageAttachmentRef,
     }))
-  } catch {
+  } catch (error: unknown) {
+    const reason = isImageAdmissionError(error)
+      ? `image admission rejected the result: ${error.message}`
+      : 'durable image storage rejected the result'
     return projectContent(content, toolName, block => ({
       type: 'text',
-      text: imageDiagnostic(block, 'durable image storage rejected the result'),
+      text: imageDiagnostic(block, reason),
     }))
   }
 }
diff --git a/packages/mcp/mcp-client/tests/mcp-client.spec.ts b/packages/mcp/mcp-client/tests/mcp-client.spec.ts
index 4ef535cfd7..7d3b2f9d77 100644
--- a/packages/mcp/mcp-client/tests/mcp-client.spec.ts
+++ b/packages/mcp/mcp-client/tests/mcp-client.spec.ts
@@ -2,7 +2,7 @@ import { describe, expect, it, vi, beforeEach } from 'vitest'
 import { Client } from '@modelcontextprotocol/sdk/client/index.js'
 import { InMemoryTransport } from '@modelcontextprotocol/sdk/inMemory.js'
 import { Context } from '@deepseek-ai/cordis'
-import AttachmentStore, { AttachmentId } from '@deepseek-ai/dsh-attachment'
+import AttachmentStore, { AttachmentError, AttachmentId } from '@deepseek-ai/dsh-attachment'
 import type { ImageAttachmentLimits, ImageAttachmentRef, SaveImageAttachment, StoredImageAttachment } from '@deepseek-ai/dsh-attachment'
 import { CallId, LlmAdapter, LlmService } from '@deepseek-ai/dsh-llm'
 import type { ContentBlock } from '@deepseek-ai/dsh-llm'
@@ -676,6 +676,29 @@ describe('tool execution', () => {
     expect(textAt(result.content)).toContain('durable image storage rejected the result')
   })
 
+  it('reports attachment policy rejection as image admission rather than storage failure', async () => {
+    const rich = await mountRichRegistry()
+    vi.spyOn(rich.attachments, 'saveImages').mockRejectedValueOnce(
+      new AttachmentError('too many images', 'TOO_MANY_IMAGES'),
+    )
+    const client = createMockClient(
+      [{ name: 'img', inputSchema: { type: 'object' } }],
+      { content: [{ type: 'image', mimeType: 'image/png', data: 'AQ==' }] },
+    )
+
+    await syncTools(client as never, rich.ctx, defaultOpts, new Map())
+    const result = await rich.ctx.tools.execute({
+      signal: testToolSignal,
+      callId: CallId('policy-rejected'),
+      name: 'mcp__srv__img',
+      arguments: {},
+      agent: agentOn() as never,
+    })
+
+    expect(textAt(result.content)).toContain('image admission rejected the result: too many images')
+    expect(textAt(result.content)).not.toContain('storage rejected')
+  })
+
   it('lets post-execute replacement win over a prepared image projection', async () => {
     const rich = await mountRichRegistry()
     rich.ctx.on('tools/post-execute', async (): Promise<PostToolDecision> => ({