Agent streaming fails with serialization error: invalid int32 overflow (4294967295)

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1

Where does the bug appear (feature/product)?

Cursor CLI

Describe the Bug

Agent streaming fails with serialization error: [internal] serialize binary: invalid int 32: 4294967295. This appears to be a signed/unsigned integer overflow in Cursor’s internal binary protocol during agent resume operations. The value 4294967295 is exactly 2^32-1, suggesting a sentinel value (-1) is being passed to a serialization layer that enforces strict int32 bounds.

Steps to Reproduce

Inconsistent, but appears to occur during:

  1. Long-running agent conversations with multiple tool calls
  2. Agent resume operations (based on stack trace showing Ryt.resume)
  3. Complex tasks that may trigger high token counts or resource tracking values

Cannot reliably reproduce on demand - seems tied to internal agent state reaching specific thresholds.

Expected Behavior

Agent streaming should handle edge-case values in resource tracking fields (token counts, step limits, etc.) before they hit the binary serialization layer. Either validate/clamp these values upstream or extend the protocol to handle sentinel values properly.

Operating System

Windows 10/11

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.4.0-pre.55.patch.0 (system setup)
VSCode Version: 1.105.1
Commit: a9fbbd7f95561f60bd6ae82aa06808d6e3700ff0
Date: 2026-01-20T02:15:43.438Z
Build Type: Stable
Release Track: Nightly
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?

Sonnet 4.5 (occurs during Agent mode operation)
Appears to happen with other models as well

For AI issues: add Request ID with privacy disabled

Request ID: 8bac3cc2-d831-4acb-8f09-aa3deef4d629

Additional Information

Full stack trace:

    at idf (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9094:26624)
    at tdf (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9094:25527)
    at vdf (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9095:4393)
    at Cfa.run (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9095:7163)
    at async Ryt.resume (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:34195:61669)
    at async opc.streamFromAgentBackend (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:34244:7695)
    at async opc.getAgentStreamResponse (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:34244:8436)
    at async TTe.submitChatMaybeAbortCurrent (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9168:74423)

This is an internal Cursor serialization bug, not user error. Workaround: start fresh conversations instead of resuming long agent sessions (but doesn’t work for longer commands).

Does this stop you from using Cursor

Sometimes - I can sometimes use Cursor

3

Hey, thanks for the report.

This is a known issue with Windows terminals. The error happens when the Agent runs commands and gets an incorrect exit code (-1), which gets converted to the unsigned int (4294967295) and breaks protobuf serialization on the client side.

Try this workaround:

  • Close Cursor completely
  • Open Settings with Ctrl + ,
  • Find terminal.integrated.defaultProfile.windows
  • Set it to “Command Prompt” instead of PowerShell
  • Restart Cursor

Sadly, based on other reports, this doesn’t always help, especially for long commands. The team is aware of the issue. Related threads:

You can subscribe to Connection Error - Serialize Binary for updates on the fix.

4

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