[internal] serialize binary: invalid int 32: 4294963248 error crashing Agent loop on Windows

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1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

I am encountering a blocking internal error in Cursor while using the Agent. The error [internal] serialize binary: invalid int 32: 4294963248 occurs repeatedly when the agent attempts to execute tasks or stream responses, specifically during the runAgentLoop execution.

Technical Detail:
The value 4294963248 (0xFFFFFFF0) exceeds the maximum value for a signed 32-bit integer (2,147,483,647). It appears the internal binary serialization (likely for IPC or Agent communication) is enforcing a signed 32-bit integer limit on a value that is effectively an unsigned 32-bit integer or a larger type, causing the serialization to fail and the agent process to crash.

Stack Trace:
[internal] serialize binary: invalid int 32: 4294963248OTe: [internal] serialize binary: invalid int 32: 4294963248 at lpf (vscode-file://vscode-app/…/workbench.desktop.main.js:9097:38348) at apf (vscode-file://vscode-app/…/workbench.desktop.main.js:9097:37251) at Cpf (vscode-file://vscode-app/…/workbench.desktop.main.js:9098:5088) at Tva.run (vscode-file://vscode-app/…/workbench.desktop.main.js:9098:9098) at async Vyt.runAgentLoop (vscode-file://vscode-app/…/workbench.desktop.main.js:34206:57104) at async mgc.streamFromAgentBackend (vscode-file://vscode-app/…/workbench.desktop.main.js:34255:7835)

Environment:
OS: Windows 10.0.26200
Context: Occurs during active Agent task execution (e.g., running shell commands or file operations).

Impact:
The error terminates the agent session immediately, making it impossible to continue with the current task.

Steps to Reproduce

  1. Open Cursor on Windows 10/11.
  2. Start a new Composer/Agent session.
  3. Input a multi-step request involving shell commands (e.g., “Run pnpm install, run DB migrations, build the project”).
  4. Allow the Agent to begin executing the plan.
  5. Observed that after receiving the request or attempting the first action, the Agent crashes with “[internal] serialize binary: invalid int 32: 4294963248”.

Expected Behavior

The Agent should be able to process the request and execute the shell commands without crashing due to internal serialization errors. The system should handle the integer values (likely related to process IDs, exit codes, or file sizes) correctly without throwing an “invalid int 32” exception.

Operating System

Windows 10/11

Version Information

Version: 2.4.32 (user setup)
VSCode Version: 1.105.1
Commit: dac77182205e080f83e43f13ee42d822740a6e10
Date: 2026-02-09T05:01:38.814Z
Build Type: Stable
Release Track: Early Access
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Windows_NT x64 10.0.26200

For AI issues: which model did you use?

Claude 4.6 max
Gemini 3 Pro Max

Does this stop you from using Cursor

Yes - Cursor is unusable

3

Hey, thanks for the report. This is a known issue on Windows. The error happens when the Agent runs commands in the terminal and gets an exit code that doesn’t fit into int32 during serialization. The value 4294963248 (0xFFFFFFF0) is most likely a negative exit code that was interpreted as unsigned.

Try switching from PowerShell to Command Prompt:

  1. Fully close Cursor
  2. Open Settings Ctrl+,
  3. Find terminal.integrated.defaultProfile.windows
  4. Set it to “Command Prompt” instead of PowerShell
  5. Restart Cursor

Main thread about this issue: Connection Error - Serialize Binary You can subscribe there to track updates.

Let me know if the workaround helped.

4

A post was merged into an existing topic: Connection Error - Serialize Binary