DeepSeek Harness for VS Code

A thin VS Code launcher for the official DeepSeek Harness Web UI, with first-class Remote SSH support and per-session Python/Conda environment selection on Bash-based hosts.

This extension does not reimplement the DeepSeek agent, chat UI, sessions, file tools, Bash tools, or model configuration. It starts the official Harness on the current VS Code workspace host, adds a small session-environment integration, and lets VS Code expose the official UI to you.

DeepSeek Harness is currently in developer preview and may introduce breaking changes.

Install the VSIX

Every successful CI run on main builds an installable artifact named:

deepseek-harness-vscode-vsix

The downloaded ZIP contains:

deepseek-harness-vscode.vsix

To install it in VS Code:

1. Open the repository's Actions tab.
2. Open the latest successful CI run.
3. Download the deepseek-harness-vscode-vsix artifact.
4. Unzip it.
5. In VS Code, open Extensions → ... → Install from VSIX....
6. Select deepseek-harness-vscode.vsix.

For Remote SSH, connect to the Linux server first. In the Extensions view, make sure DeepSeek Harness is installed/enabled for the SSH host. Because this extension is a workspace extension, the launcher runs in the remote Extension Host.

What it does

When you run DeepSeek Harness: Open in VS Code, the extension:

1. Finds the current VS Code workspace folder.
2. Installs its small session-environment host plugin into the Harness module fallback under $DSH_HOME and supplies it through a temporary Harness --patch overlay.
3. Runs the official Harness from the workspace folder on port 3080.
4. Waits for the Harness Web UI to become available on 127.0.0.1:3080.
5. Calls vscode.env.asExternalUri(...) so Remote SSH ports are reachable from the local VS Code client.
6. Opens the forwarded URL in VS Code's built-in Simple Browser.

The invoking directory is therefore the Harness workspace. The extension does not require pnpm on the remote host; Node.js/npm/npx are sufficient for the launcher path.

Architecture

Local workspace

Local VS Code
    │
    ├─ extension
    │    │
    │    └─ npx @deepseek-ai/dsh --profile web ... --port 3080
    │
    └─ official DeepSeek Harness Web UI

Remote SSH workspace

Your local computer
┌─────────────────────────────────────┐
│ VS Code                             │
│                                     │
│ Simple Browser                     │
│     ▲                               │
└─────┼───────────────────────────────┘
      │ VS Code Remote port forwarding
      │
      ▼
Remote Linux server (no GUI required)
┌─────────────────────────────────────┐
│ VS Code Server / Extension Host     │
│                                     │
│ deepseek-harness-vscode             │
│          │                          │
│          ├─ session-env integration │
│          │                          │
│          ▼                          │
│ npx @deepseek-ai/dsh                │
│ --profile web --port 3080           │
│          │                          │
│     127.0.0.1:3080                  │
│          │                          │
│          ├─ Harness Agent           │
│          ├─ Bash                    │
│          ├─ filesystem tools        │
│          ├─ sessions                │
│          └─ official Web UI         │
│                                     │
│ /home/user/project                  │
└─────────────────────────────────────┘

The remote Linux server does not need a desktop environment, X11, or a browser. It only runs the HTTP service. The UI is rendered on your local computer.

Remote SSH

1. Connect using Remote-SSH: Connect to Host....

2. Open the project folder on the remote server.

3. Install/enable this extension on the SSH host when VS Code prompts you.

4. Make sure Node.js/npm are available on the remote server:

   node --version
   npm --version
   npx --version
   

5. Click the DeepSeek Harness item in the VS Code status bar, or run:

   DeepSeek Harness: Open in VS Code
   

The extension declares:

"extensionKind": ["workspace"]

so under Remote SSH the launcher itself runs inside the remote VS Code Extension Host. The dsh process, Bash commands, and file access therefore operate on the remote Linux workspace.

Per-session Python / Conda environments

On Linux/macOS Bash-based Harness sessions, every official Harness session can use a different Python environment.

When a session reaches its first Bash tool call, the integration checks whether that session already has an environment selection. If not, it detects available environments and presents the official Harness option picker before the Bash command runs. If no alternate environment is detected, the Harness default environment is selected automatically.

Detected choices include:

• ./.venv
• ./venv
• ./env
• environments returned by conda env list --json
• the environment inherited by the Harness process

The selection is keyed by the official Harness session ID. For example:

Session A → .venv
Session B → conda: pytorch
Session C → Harness default

Those sessions can remain open simultaneously without changing each other's future Bash environment.

/env command

The integration registers a normal Harness slash command:

/env

Use it at any time in the current session to open the environment picker and switch environments.

Other forms:

/env status
/env system
/env .venv
/env conda: pytorch
/env /home/user/miniconda3/envs/pytorch

/env status shows the current binding. /env system returns the session to the environment inherited by Harness. A relative or absolute environment directory can be supplied directly when it is not in the detected list.

How session isolation works

Official Harness Bash calls are separate non-interactive bash -c processes, so a one-time source .venv/bin/activate would not persist. Instead, the launcher supplies a small BASH_ENV bootstrap. Every Bash process receives the official DSH_SESSION_ID, and the bootstrap loads only that session's saved environment file before the command executes.

The environment selection therefore affects future Harness Bash calls in that session. It does not activate the user's SSH terminal and does not alter another Harness session. A Bash process that is already running keeps the environment with which it started.

Harness-created subagents inherit their parent session's environment instead of opening an interaction that a delegated agent cannot answer.

Current scope: this feature targets the Harness Bash execution path on Linux/macOS, especially VS Code Remote SSH to Linux. Native Windows/PowerShell session environment switching and non-Bash runtimes such as a separate Code Mode worker are not yet remapped per session.

VS Code commands

• DeepSeek Harness: Open in VS Code — start if necessary and open the official UI in VS Code.
• DeepSeek Harness: Open in Browser — start if necessary and open the forwarded UI in your normal browser.
• DeepSeek Harness: Start — start the official Harness without opening the UI.
• DeepSeek Harness: Stop — stop a Harness process started by this extension.
• DeepSeek Harness: Restart — restart it.
• DeepSeek Harness: Show Logs — show npx / Harness output.

Settings

The first launch can take longer because npx may need to download the Harness package.

DeepSeek API configuration

API keys, models, sessions, tools, approvals, skills, and other agent settings belong to the official DeepSeek Harness UI. This VS Code extension intentionally does not duplicate them.

Port forwarding and security

Harness remains on the workspace host at:

127.0.0.1:<port>

The extension asks VS Code to produce an externally reachable URI for that address using vscode.env.asExternalUri. In a Remote SSH session, VS Code handles the tunnel between the remote host and your local client.

You do not need to expose port 3080 publicly on the Linux server.

Existing Harness process

If the configured port is already listening when the extension starts, the extension reuses that service rather than launching a duplicate process.

For safety, Stop only terminates a process owned by this extension. It will not kill an unknown process that was already listening on the configured port.

Per-session /env integration is guaranteed only when the Harness process was started by this extension, because an already-running external process cannot retroactively receive the patch or BASH_ENV launch environment.

Development

git clone https://github.com/plutoczm/deepseek-harness-vscode.git
cd deepseek-harness-vscode
npm install
npm run compile
npm run package

npm run package creates:

deepseek-harness-vscode.vsix

Press F5 to launch an Extension Development Host.

Upstream

• DeepSeek Harness: https://github.com/deepseek-ai/deepseek-harness
• Harness homepage: https://deepseek.com/harness

This project is an independent VS Code integration and is not an official DeepSeek AI product.

License

MIT