Windows cursor-agent 2026.08.11-e8db854 hangs after editToolCall write; process never exits, empty stderr

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1

Where does the bug appear (feature/product)?

Cursor CLI

Describe the Bug

editToolCall streams the new file contents (streamContent). The file is written on disk. Then:

  1. No tool_call subtype: completed event is ever emitted for that edit
  2. No result event
  3. The process never exits
  4. stderr is empty
  5. Open Design’s inactivity watchdog kills it after 600s (AGENT_EXECUTION_FAILED / inactivity_timeout)
    This is not an approval wait: Open Design telemetry for the real run recorded approval_requested: false. Glob/Read tool calls in the same session complete normally; only the write hangs.

Minimal repro (small)

Workspace: a folder containing only DESIGN.md.

Steps to Reproduce

Append a single HTML comment at the end of DESIGN.md in this workspace, then reply DONE. Keep it minimal.
Observed NDJSON (session df51e6ee-84b7-4487-ab05-669f7becafd3):

  1. system/init — ok
  2. globToolCall **/DESIGN.md — completed
  3. readToolCall of DESIGN.md — completed
  4. editToolCall started with streamContent ending in <!-- small edit test -->
  5. silence — no completed event, no result, process still running, empty stderr

Real repro (design write)

Same hang writing a full HTML artifact (homepage-preview.html) after a long thinking/read pass.

  • session_id: 3c362e17-e27d-4c54-b6d6-1416034ab0cc
  • Last event: tool_call / editToolCall / subtype: started (call-492a85f8-07ec-4528-8c34-769bc67ac89a-36)
  • Open Design run f0e1e94d-7f06-4848-aec8-a54c7724be25: stalled 600s, artifact_write_seen: true, tool_call_seen: false (host never got a completed tool result), stderr_present: false, stdin_backpressure: true

Screenshots / Screen Recordings

repro-small.log (18.4 KB)repro-real.log (433 KB)

Operating System

Windows 10/11

Version Information

  • Product: Cursor CLI (cursor-agent / agent), not the IDE Agent chat
  • Version: 2026.08.11-e8db854 (August 11, 2026 release — currently the latest on the public changelog)
  • OS: Windows 11 (10.0.26200)
  • Account: logged-in CLI (apiKeySource: login)
  • Host: Open Design desktop (nexu-io/open-design) spawning headless cursor-agent for design artifact writes; also reproduced with a minimal one-file prompt outside Open Design
  • CLI config (%USERPROFILE%\.cursor\cli-config.json): approvalMode: allowlist, sandbox.mode: disabled, network.useHttp1ForAgent: false, model: Auto
  • Hooks: ~/.cursor/hooks.json is empty ("hooks": {}) — not the Windows Claude-hooks hang
  • agent about --format json: cliVersion 2026.08.11-e8db854, osPlatform win32, osArch x64, subscriptionTier Pro, lastRequestId null

For AI issues: which model did you use?

Auto

Additional Information

  • Product: Cursor CLI (cursor-agent / agent), not the IDE Agent chat
  • Version: 2026.08.11-e8db854 (August 11, 2026 release — currently the latest on the public changelog)
  • OS: Windows 11 (10.0.26200)
  • Account: logged-in CLI (apiKeySource: login)
  • Host: Open Design desktop (nexu-io/open-design) spawning headless cursor-agent for design artifact writes; also reproduced with a minimal one-file prompt outside Open Design
  • CLI config (%USERPROFILE%\.cursor\cli-config.json): approvalMode: allowlist, sandbox.mode: disabled, network.useHttp1ForAgent: false, model: Auto
  • Hooks: ~/.cursor/hooks.json is empty ("hooks": {}) — not the Windows Claude-hooks hang
  • agent about --format json: cliVersion 2026.08.11-e8db854, osPlatform win32, osArch x64, subscriptionTier Pro, lastRequestId null

Does this stop you from using Cursor

Yes - Cursor is unusable

5

Hey, thanks for the report. We don’t often see such a clean minimal repro with full NDJSON logs, that really helps. The symptom makes sense: the file is written to disk, but completed and result for editToolCall never arrive, so the process hangs until the 600s watchdog. stderr is empty. I’ve passed this to the team.

While we dig in, here are a couple of diagnostic steps that would be helpful to try on your minimal repro (DESIGN.md):

  1. Move the workspace outside %LOCALAPPDATA%\Temp (for example, to C:\repro\) and run the same repro again.
  2. Or add a Windows Defender or antivirus exclusion for the workspace folder and retry.

If the hang goes away in either case, let me know. That would narrow things down a lot. Also, can you confirm if this reproduces on the previous CLI version 2026.08.04-aaa8809, or not?

I’ll post an update here once we have one.

7

Follow-up diagnostics from the DESIGN.md repro:

  1. Workspace outside %LOCALAPPDATA%\Temp
    Moved the same one-file workspace to C:\repro and reran:
    cursor-agent -p --output-format stream-json --force --trust --workspace C:\repro
    with prompt: append to DESIGN.md, then reply DONE.

Hang still happens. DESIGN.md is written on disk. NDJSON stops at tool_call/editToolCall subtype=started. No completed event for that edit, no result event, empty stderr. Process was still running at 90s and had to be killed.
session_id: fb5b64a6-aba2-4ce9-8e6e-25ae0150945f
last call_id: call-208bec83-cc89-4299-a484-b1ec7850e711-2

So this is not specific to Temp.

  1. Antivirus exclusion
    Windows Defender real-time protection is off on this machine (AMServiceEnabled/AntivirusEnabled/RealTimeProtectionEnabled = False). Add-MpPreference -ExclusionPath C:\repro failed: not enough permissions.
    The active product is ESET Security (ecmds.exe). I did not add an ESET exclusion from CLI. Happy to retry if you want an ESET folder exclusion specifically.

  2. Previous CLI 2026.08.04-aaa8809
    Installed that build side-by-side (did not replace 2026.08.11) and ran the same repro at C:\repro-old.

It hangs the same way: file written, editToolCall started, no completed, no result, empty stderr, killed at 90s.
session_id: f9aa3c87-e2fb-4df3-9b18-c731cf64f037
last call_id: call-5434cc98-0bd7-453e-bb58-0189810ccc3b-2

This does not look like an 2026.08.11-only regression.

(attachments)

out-2026.08.04-aaa8809.log (5.68 KB)

8

Thanks, this is really thorough debugging. These three points rule out a few hypotheses right away:

  • It’s not an issue with %LOCALAPPDATA%\Temp since it’s the same in C:\repro.
  • It’s not a 2026.08.11 regression since 2026.08.04-aaa8809 behaves the same.
  • Defender real-time protection is off and ESET is active.

I passed these details and the session IDs to the team.

Since ESET is the only active AV right now and we haven’t tested an exclusion yet, yep, let’s do the test you suggested. Add C:\repro to ESET exclusions for real-time or file system protection, then run the same minimal repro with DESIGN.md. If the hang goes away, that narrows it down a lot.

One more isolation check. Does the same thing happen on another Windows machine, ideally without ESET, using the same minimal one-file workspace? That’ll help confirm if this is specific to your environment or Windows in general.

I’ll reply here once I have an update.