Codex for Visual Studio v0.4.0 / v0.4.1 Released

Translation note: The original Japanese article was written by me. This English version was translated with the help of AI.

I've released v0.4.0 and v0.4.1 of Codex for Visual Studio, a Visual Studio extension that lets you use Codex directly from Visual Studio.

Version 0.4.0 contains the main feature additions, while v0.4.1 includes dependency updates and smaller fixes.

• Marketplace: https://marketplace.visualstudio.com/items?itemName=KazushiKamegawa.relaytocodexforvs
• v0.4.0 Release Notes: https://github.com/kkamegawa/vsextensionforcodex/releases/tag/v0.4.0
• v0.4.1 Release Notes: https://github.com/kkamegawa/vsextensionforcodex/releases/tag/v0.4.1

The main changes in this release are:

1. Improved Goal / Plan mode behavior
2. Remote Codex App Server support (Experimental)
3. MXC sandbox support
4. Updated for Codex CLI 0.162.1
5. Other bug fixes

1. Improved Goal / Plan Mode Behavior

Previously, when a goal started with /goal was running, the button remained labeled Send, making it impossible to stop execution.

Starting with v0.4.0, the button changes to Stop whenever a goal is active, including between turns during automatic continuation.

When Stop is pressed:

1. The goal is paused while preserving its objective, budget, and usage.
2. The latest turn in the thread is interrupted.

Timed-out operations are treated as having an unknown outcome and are not retried automatically, preventing unexpected re-execution.

Plan mode received several related improvements:

Persistent Plan Mode

A checkbox has been added to the composer.

Using /plan also enables it.

Once enabled, Plan mode stays active until explicitly turned off, even if turns complete, fail, or are interrupted. If Codex asks follow-up questions, Plan mode remains active throughout the conversation.

Codex-style Plan Presentation

Suggested plans are displayed as Markdown under "Proposed plan".

When a plan turn finishes, an "Implement this plan?" card appears, allowing you to either:

• Proceed with implementation
• Continue refining the plan

Experimental API Detection

Plan mode relies on the App Server's experimental collaborationMode field.

Because Codex rejects this field when Experimental APIs are unavailable, the extension now determines availability based on the currently negotiated connection rather than saved settings.

When unsupported:

• The Plan checkbox becomes disabled
• Entering /plan explains how to enable the feature

One Question at a Time

When multiple questions arrive, they are presented individually using a "Question n of N" workflow.

This also fixes earlier issues where answer choices could become partially hidden.

Stop Works After Questions and Implementation

Fixed an issue where the Stop button stopped working after:

• Starting implementation from a plan
• Answering a question

Choices Embedded in Text Become Cards

When Codex returns numbered or bulleted choices in normal text, those options are now converted into interactive question cards.

v0.4.1 Goal Confirmation Fix

v0.4.1 fixes an issue where the final goal confirmation message failed to display the Yes/No card if the confirmation text was formatted in bold Markdown.

2. Connect to a Remote Codex App Server (Experimental)

The extension can now connect to an already-running Codex App Server through WebSocket.

This feature is currently marked as Experimental.

The default behavior remains unchanged:

• The extension launches codex app-server locally as a child process.
• Communication uses stdio.

Internally, the extension still communicates with its local Worker. The Worker decides whether the backend transport should be stdio or WebSocket.

Security and Connection Design

• Remote connections require wss
• Plain ws is allowed only for loopback (localhost)
• Certificate validation cannot be disabled

Authentication uses Bearer tokens.

Profiles store only the path to the token file.

The Worker reads the token during connection establishment, and the token itself is never persisted in configuration files or logs.

Path Mapping

The extension maps:

• Local solution root
• Remote server root

Path matching is performed component-by-component rather than through string replacement.

For example:

C:\repo

will not match:

C:\repo2

The implementation should also reject paths that escape through symlinks or junctions, although I have not yet fully validated those scenarios.

Connection Isolation

Approvals, caches, and related state are isolated by:

• Connection
• Account

This prevents leakage between different server connections.

Reconnection Behavior

When a connection drops:

• Automatic reconnection is attempted
• Draft messages remain in memory
• Operations with unknown delivery status are never retried automatically

Separate Commands

Local connections use:

Restart local app-server

Remote connections use:

Reconnect remote app-server

The extension never attempts to stop a remote server.

Setup Guide

I also added:

• doc/codex-cli-setup.md
• doc/codex-cli-setup_ja.md

The guide covers:

• CLI installation
• Authentication
• Configuration files
• Connection target settings
• Remote App Server setup
• Reconnection
• Diagnostics

So far I've only tested loopback connections on the same machine.

I haven't yet validated:

• Cross-machine connections
• TLS deployments
• Cross-platform path translation

If you try those scenarios, I'd love to hear your feedback.

3. MXC Sandbox Support

For local App Server scenarios, you can now choose MXC as the Windows sandbox backend.

The Windows sandbox panel now provides three options:

Option	Setting	Behavior
Follow Codex configuration	None	Uses Codex configuration
Prefer MXC	-c features.prefer_mxc=true	Uses MXC when policy permits
Require MXC	-c windows.sandbox=mxc	Always uses MXC

Changes take effect the next time the local App Server starts.

Remote profiles are unaffected.

Sandbox Status

The Check sandbox status action shows:

• Effective configuration
• Policy status

Although it cannot determine which backend executed a specific command.

MXC itself requires no setup.

The elevated/unelevated setup options shown in the UI apply only to the traditional sandbox backends.

MXC Observation

While testing, I noticed that force-terminating only the root Codex process under MXC may leave child processes running.

This does not occur with the unelevated backend.

Since the extension shuts down the entire process tree, users should not encounter this issue during normal use.

4. Updated for Codex CLI 0.162.1

Communication with the App Server has been updated for compatibility with Codex CLI 0.162.1.

Because some remote servers may still use older versions, I continue to keep 0.159.1 available for regression testing.

Extension ↔ Worker Protocol Updates

The protocol version between the extension and Worker has also been updated.

Version 23 introduces:

• Experimental API status reporting

which enables the new Plan mode availability checks.

MXC support adds protocol version 24.

Unsupported combinations fail safely rather than attempting to continue with incompatible behavior.

Additional 0.162.1-related changes include:

• Goal operations now send origin: "user" for proper authorization handling
• MCP OAuth completion is matched using loginId
• Skill paths are now treated as server-provided identifiers rather than requiring absolute paths

5. Other Notable Fixes

• Fixed a banner that failed to disappear after successful manual reconnection
• Fixed a state where loading a remote token could leave the UI stuck at "Connecting / Checking account"
• Improved readability of question cards in dark themes by using Visual Studio theme resources
• Added an MCP details toggle to collapse MCP server information
• Missing or unreadable attachments now cause send operations to fail instead of being silently skipped
• v0.4.1 updates NuGet dependencies, including MessagePack packages affected by a published vulnerability

Closing Thoughts

This release primarily focuses on improving Goal and Plan mode usability while laying the groundwork for remote connectivity.

Remote App Server support is still experimental, so please file an issue if you encounter problems.

To install:

• Download Codex.VisualStudio.Extension.vsix from GitHub Releases and double-click it, or
• Install directly from the Visual Studio Marketplace

Visual Studio 17.14 or later is required.

What's Next?

After .NET 8 reaches end-of-support, I plan to fully migrate the extension to .NET 10.

At that point, Visual Studio 2026 or later will be required.