[Windows][Codex Desktop 26.825.31414] New GPT-5.6 Terra tasks fail local workspace handshake; 5.5→5.6 recovers the same task

Environment

• Product: ChatGPT / Codex Desktop
• App version: 26.825.31414
• Release date shown in About dialog: 2026-08-28
• Platform: Windows x64
• Authentication: ChatGPT account
• Affected model: GPT-5.6 Terra
• Control model: GPT-5.5
• Workspace: ordinary local folder on the Windows filesystem (exact user path omitted for privacy)

What issue are you seeing?

A newly created Codex Desktop task using GPT-5.6 Terra intermittently/frequently cannot read the local workspace because the local command execution service fails to initialize. The UI reports a local execution / handshake failure and says it cannot access the folder.

The important A/B behavior is that the exact same folder becomes readable immediately after switching the same task to GPT-5.5. If the task is then switched back to GPT-5.6 Terra, GPT-5.6 can read the folder successfully. However, creating another new task directly with GPT-5.6 Terra reproduces the failure again.

Observed sequence:

New task + GPT-5.6 Terra
  -> ask to read/list workspace
  -> local command execution service / handshake fails
  -> workspace cannot be read

Same task -> switch to GPT-5.5
  -> ask to read/list the exact same workspace
  -> succeeds immediately

Same task -> switch back to GPT-5.6 Terra
  -> workspace reading now succeeds

Create another new task + GPT-5.6 Terra
  -> failure returns

This strongly suggests a new-task Code Mode / local runtime initialization problem rather than a filesystem permission or workspace-path problem.

Steps to reproduce

1. Launch Codex Desktop on Windows, version 26.825.31414.
2. Open/select a normal local workspace.
3. Create a new task/conversation using GPT-5.6 Terra.
4. Ask it to read the current folder and list its files.
5. Observe that local execution fails to initialize; the UI reports a handshake/local command execution error and the folder cannot be read.
6. In the same task, switch the model to GPT-5.5.
7. Ask it to read/list the same folder again.
8. Observe that GPT-5.5 succeeds and lists the files.
9. Switch the same task back to GPT-5.6 Terra.
10. Ask it to read/list the folder again.
11. Observe that GPT-5.6 Terra now succeeds.
12. Create a new task directly with GPT-5.6 Terra and repeat the read/list request.
13. Observe that the handshake/local execution failure returns.

Expected behavior

A new GPT-5.6 Terra task should initialize the local Code Mode / command execution host and access the selected workspace directly, without requiring a GPT-5.5 turn first.

Changing models inside a task should not be required to make filesystem/shell tools available.

Actual behavior

GPT-5.6 Terra can fail during local execution initialization in a fresh task. GPT-5.5 can initialize/use the exact same local workspace successfully. After GPT-5.5 succeeds, switching that same task back to GPT-5.6 Terra makes GPT-5.6 work, but a newly created GPT-5.6 task can fail again.

Why this reproduction is useful

The model-switch behavior provides a controlled comparison:

• same machine
• same Codex Desktop installation
• same account
• same workspace
• same filesystem permissions
• same application session

The main changed variable is the model / task initialization path.

Because GPT-5.5 succeeds on the exact same folder, and GPT-5.6 can subsequently succeed in that same task, a permanently inaccessible folder or broken Windows permission setup is unlikely.

Workaround

For each new task:

1. Start or switch to GPT-5.5.
2. Perform one local filesystem operation successfully (for example, list the workspace files).
3. Switch the same task back to GPT-5.6 Terra.
4. Continue working with GPT-5.6.

This workaround has been reproducible, but it must be repeated for new GPT-5.6 tasks.

Related issues

Possibly related, but this report adds a distinct new-task initialization + same-task recovery after 5.5 signal:

• #40798 — Windows Codex Desktop 26.820: GPT-5.6 tool calls fail with code-mode host exited during handshake, while GPT-5.5 works.
• #32759 — GPT-5.6 shell/tool execution fails with code-mode host exited during handshake on another platform/CLI.

The issue is still reproducible on the newer Desktop build 26.825.31414 released on 2026-08-28.

Additional information

A screenshot was captured showing the sequence in the Desktop UI: initial GPT-5.6 local execution handshake failure, successful GPT-5.5 directory listing in the same task, successful GPT-5.6 after switching back, and failure recurring in a newly opened GPT-5.6 task. It can be provided if maintainers need it.

Start by reproducing the new-task GPT-5.6 Terra sequence on Windows: compare the local command execution handshake before and after a GPT-5.5 turn. Investigate the new-task Code Mode or local runtime initialization path mentioned in the report. Done means a fresh GPT-5.6 task can access the selected workspace without switching models first.