diff --git a/packages/cordis/tool-cordis/tests/mount.spec.ts b/packages/cordis/tool-cordis/tests/mount.spec.ts
index 6bc2d5970d..a46f37a721 100644
--- a/packages/cordis/tool-cordis/tests/mount.spec.ts
+++ b/packages/cordis/tool-cordis/tests/mount.spec.ts
@@ -433,6 +433,7 @@ describe('cordis_mount', () => {
                 ['__proto__']: { type: 'string', required: true },
                 value: { type: 'json', default: { ['__proto__']: { safe: true } } },
               },
+              ${CONTENT_OUTPUT_CODE}
               async execute() { return [] },
             }))
           },
diff --git a/packages/core/agent-loop/tests/coverage-edges.spec.ts b/packages/core/agent-loop/tests/coverage-edges.spec.ts
index 65c2258d0b..eb1a456c7a 100644
--- a/packages/core/agent-loop/tests/coverage-edges.spec.ts
+++ b/packages/core/agent-loop/tests/coverage-edges.spec.ts
@@ -274,6 +274,6 @@ describe('structured tool error propagation (the runtime-validation Agent Note,
     const toolResult = agent.session.events.find(e => e.type === 'tool/result')
     expect(toolResult?.type === 'tool/result' && toolResult.data.isError).toBe(true)
     expect(toolResult?.type === 'tool/result' && toolResult.data.error)
-      .toEqual({ message: 'exploded', info: { name: 'HarnessError', code: 'BOOM' } })
+      .toEqual({ name: 'HarnessError', code: 'BOOM' })
   })
 })
diff --git a/packages/core/agent-loop/tests/loop.spec.ts b/packages/core/agent-loop/tests/loop.spec.ts
index aa3a35bc36..3c89eda70c 100644
--- a/packages/core/agent-loop/tests/loop.spec.ts
+++ b/packages/core/agent-loop/tests/loop.spec.ts
@@ -253,7 +253,7 @@ describe('agent loop', () => {
     ['BigInt', { n: 1n }],
     ['Map', new Map([['key', 'value']])],
     ['class instance', new (class ResultMeta { x = 1 })()],
-  ])('normalizes non-JSON presentation metadata (%s) before the durable result commit', async (_kind, meta) => {
+  ])('rejects non-JSON presentation metadata (%s) before the durable result commit', async (_kind, meta) => {
     const adapter = new MockAdapter([
       toolCallResponse('bad-meta-call', 'bad-meta', {}, 'calling'),
       textResponse('recovered'),
@@ -281,15 +281,16 @@ describe('agent loop', () => {
       expect(result.data.callId).toBe('bad-meta-call')
       expect(result.data.isError).toBe(true)
       expect(result.data.meta).toBeUndefined()
+      expect(result.data.error).toEqual({ name: 'ToolOutputError', code: 'INVALID_TOOL_OUTPUT' })
       expect(result.data.content).toEqual([{
         type: 'text',
-        text: 'Error: tool result must be losslessly JSON-serializable',
+        text: 'Error: tool "bad-meta" returned invalid output: output.presentationMeta returned non-lossless JSON',
       }])
     }
     // The normalized failure was durably logged and fed back to the model; the
     // turn continued normally instead of failing after an apparent success.
     expect(adapter.requests).toHaveLength(2)
-    expect(JSON.stringify(adapter.requests[1]!.messages)).toContain('losslessly JSON-serializable')
+    expect(JSON.stringify(adapter.requests[1]!.messages)).toContain('output.presentationMeta returned non-lossless JSON')
   })
 
   it('omits the system field when a system-prompt/assemble veto empties the assembly', async () => {
diff --git a/packages/core/tools/tests/tools.spec.ts b/packages/core/tools/tests/tools.spec.ts
index d237430dda..874500ed3f 100644
--- a/packages/core/tools/tests/tools.spec.ts
+++ b/packages/core/tools/tests/tools.spec.ts
@@ -1,6 +1,6 @@
 import { describe, expect, expectTypeOf, it } from 'vitest'
 import { Context } from 'cordis'
-import { CallId, HarnessError } from '@deepseek-ai/dsh-llm'
+import { CallId, HarnessError, type ContentBlock } from '@deepseek-ai/dsh-llm'
 import SystemPrompt from '@deepseek-ai/dsh-system-prompt'
 import type { Agent } from '@deepseek-ai/dsh-agent'
 import ApprovalService, { type ApprovalOutcome, type ApprovalRequest } from '@deepseek-ai/dsh-user-approval'
@@ -217,6 +217,35 @@ describe('ToolRegistry', () => {
     expect('value' in result).toBe(false)
   })
 
+  it.each(['render', 'presentationMeta'] as const)('contains a throwing output.%s snapshot as one failed call', async (projector) => {
+    const ctx = await setup()
+    const hostile = Object.defineProperty({}, 'value', {
+      enumerable: true,
+      get: () => { throw new Error('snapshot getter exploded') },
+    })
+    ctx.tools.register(defineTool({
+      name: `hostile-${projector}`,
+      description: projector,
+      parameters: {},
+      output: {
+        schema: { type: 'string' },
+        render: () => projector === 'render'
+          ? hostile as unknown as ContentBlock[]
+          : [{ type: 'text', text: 'ok' }],
+        presentationMeta: () => projector === 'presentationMeta'
+          ? hostile as unknown as JsonValue
+          : null,
+      },
+      execute: async () => 'ok',
+    }))
+
+    const result = await ctx.tools.execute({
+      callId: CallId(`hostile-${projector}`), name: `hostile-${projector}`, arguments: {},
+    })
+    expect(result.error?.message).toContain('snapshot getter exploded')
+    expect(result.error?.info).toEqual({ name: 'ToolOutputError', code: 'INVALID_TOOL_OUTPUT' })
+  })
+
   it('keeps value/meta through content replacement and recomputes both projections after value replacement', async () => {
     const ctx = await setup()
     ctx.tools.register(defineTool({
diff --git a/packages/fs/tool-fs/src/read-render.ts b/packages/fs/tool-fs/src/read-render.ts
index e30dad7bcd..943ff98f61 100644
--- a/packages/fs/tool-fs/src/read-render.ts
+++ b/packages/fs/tool-fs/src/read-render.ts
@@ -77,7 +77,6 @@ function lineByteSize(line: string, currentLineCount: number): number {
 
 function consumeLine(acc: WindowAccumulator, rawLine: string, request: ReadWindow): void {
   acc.totalLines += 1
-  if (acc.done) return
   if (acc.totalLines < request.offset || acc.lines.length >= request.limit) return
 
   const text = truncateLine(rawLine, request.maxLineLength)
diff --git a/packages/mcp/mcp-client/tests/apply.spec.ts b/packages/mcp/mcp-client/tests/apply.spec.ts
index 4b43411346..e36e091478 100644
--- a/packages/mcp/mcp-client/tests/apply.spec.ts
+++ b/packages/mcp/mcp-client/tests/apply.spec.ts
@@ -15,14 +15,26 @@ import type { Config } from '@deepseek-ai/dsh-mcp-client'
 const { mockConnect, mockClose, mockListTools, mockCallTool, mockSetNotificationHandler, MockClient } = vi.hoisted(() => {
   const mockConnect = vi.fn<() => Promise<void>>()
   const mockClose = vi.fn<() => Promise<void>>()
-  const mockListTools = vi.fn()
-  const mockCallTool = vi.fn()
+  const mockListTools = vi.fn<(_params?: Record<string, unknown>) => Promise<unknown>>()
+  const mockCallTool = vi.fn<(
+    _params?: Record<string, unknown>, _compatibilitySchema?: unknown, _options?: unknown,
+  ) => Promise<unknown>>()
   const mockSetNotificationHandler = vi.fn()
+  const mockRequest = vi.fn(async (
+    request: { method: string; params?: Record<string, unknown> },
+    _schema: unknown,
+    options?: unknown,
+  ): Promise<unknown> => {
+    if (request.method === 'tools/list') return await mockListTools(request.params)
+    if (request.method === 'tools/call') return await mockCallTool(request.params, undefined, options)
+    throw new Error(`unexpected MCP request: ${request.method}`)
+  })
   class MockClient {
     connect = mockConnect
     close = mockClose
     listTools = mockListTools
     callTool = mockCallTool
+    request = mockRequest
     setNotificationHandler = mockSetNotificationHandler
   }
   return { mockConnect, mockClose, mockListTools, mockCallTool, mockSetNotificationHandler, MockClient }