dsh-mcp-bridge

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Expose a running DeepSeek Harness (DSH) instance over the Model Context Protocol, so an external agent — Codex, or any MCP client — can drive that instance's own sessions.

A DSH session behaves like a subagent from the caller's point of view: it keeps its own context across calls, works in the workspace you name, and returns a final answer. The bridge also lets the caller answer the questions that DSH agent asks, so a delegated task never deadlocks waiting for a human who is not there.

Why

Driving a DSH instance through its web GUI from another agent costs a screenshot or DOM round trip per step. This bridge replaces that with a small structured API: one tool call in, one result out.

Related MCP server: dsh-web-bridge-mcp

Architecture

MCP client (stdio)
 └── bin/dsh-mcp.mjs          MCP server; polls the bridge, holds questions for the caller
      └── HTTP 127.0.0.1:<port>/dsh-bridge
           └── lib/index.js    host Cordis plugin mounted inside the running DSH process
                └── ctx.sessionController → DSH agent

Two halves, and the split matters:

• lib/index.js is a DSH host plugin. It runs in the same process as the Web GUI, so it can read and write the sessions that instance already has. It registers an HTTP route and does the DSH work.

• bin/dsh-mcp.mjs is a standalone MCP server that speaks stdio to your agent and HTTP to the plugin. It exists because DSH's own process owns stdout, so the plugin cannot serve stdio itself.

Waiting and polling happen in the MCP server, where they cost nothing; your model spends one tool call and receives the finished result.

Requirements

• DSH with a Web profile (dsh web or the desktop app).

• Node.js 18 or newer on the same machine as DSH.

• An MCP client that can spawn a stdio server.

Install the plugin

Install straight from this repository — the package is not published to npm:

dsh plugin --profile web add github:Nigheart/dsh-mcp-bridge

Then restart DSH. On startup the log should show:

[dsh-mcp-bridge] mounted /dsh-bridge (tokenRequired=false)

Verify it independently:

curl -s http://127.0.0.1:3080/dsh-bridge/ping
# {"ok":true,"data":{"bridge":"dsh-mcp-bridge","version":"0.3.0","tokenRequired":false}}

If your instance listens on a port other than 3080, use that port here and set DSH_BRIDGE_URL for the MCP server (below).

Manual install

If you prefer to wire it up by hand, add the package to the profile's package.json and list it as a bundle:

{
  "dependencies": { "dsh-mcp-bridge": "github:Nigheart/dsh-mcp-bridge" },
  "dsh": { "profile": { "bundles": ["@deepseek-ai/dsh-base", "@deepseek-ai/dsh-web-app", "dsh-mcp-bridge"] } }
}

The package ships its own cordis.patch.yml, which inserts one loader row. That row declares inject: [webServer, sessionController] — keep it. Without inject the plugin can be activated before those services exist, find nothing to bind to, and mount no route at all.

Configure your MCP client

Codex (~/.codex/config.toml):

[mcp_servers.dsh]
command = "node"
args = ["/absolute/path/to/dsh-mcp-bridge/bin/dsh-mcp.mjs"]
startup_timeout_sec = 60

# Only needed when DSH is not on the default port, or when a token is set.
[mcp_servers.dsh.env]
DSH_BRIDGE_URL = "http://127.0.0.1:8080/dsh-bridge"

The server sends its own usage notes in the MCP handshake (initialize.instructions), so the client learns the workflow without any extra prompting.

Environment variables:

Tools

Delegating work

dsh_delegate({ workspace: "/home/me/project", instruction: "Add the missing tests for parser.js" })

Omit sessionId to start a new DSH agent; pass the returned sessionId back to continue the same agent, which still remembers the earlier work. status tells you what happened:

Answering questions

By default a delegated session runs under takeover: when the DSH agent calls its question tool, the call is suspended and handed to the caller instead of the GUI. dsh_delegate then returns immediately with the question rather than waiting:

{
  "status": "waiting",
  "waiting": {
    "kind": "user-question",
    "toolName": "ask_user_question",
    "intercepted": true,
    "detail": [{ "id": "choice", "question": "Which database?", "options": ["sqlite", "postgres"] }]
  }
}

Answer it with the ids from detail:

dsh_answer({ sessionId, answers: [{ id: "choice", selected: ["sqlite"] }] })

If nobody answers within about three minutes, the question falls back to the DSH GUI, so an unattended delegation cannot hang forever. Pass takeover: false to dsh_delegate to leave questions with the GUI from the start.

Approvals

Some operations need a decision before DSH will run them — for example escalating a sandbox so a tool can write outside the session workspace. The session then reports:

{
  "status": "waiting",
  "waiting": {
    "kind": "approval",
    "detail": [{
      "id": "d0f853e3-...",
      "toolName": "pwsh",
      "callId": "call_00_...",
      "reason": "escalate sandbox to danger-full-access: ... outside the session workspace"
    }]
  }
}

reason is DSH's own explanation of what it wants and why, so the caller can judge whether granting it is appropriate.

An approval that is already pending has only two exits: a person answers it in the DSH Web GUI, or the turn is abandoned with dsh_cancel. Nothing below can rescue the request that is already open.

dsh_approval({ sessionId, mode }) decides how future approvals in that session are handled. The policy takes effect at the agent's next step, so it never applies retroactively:

• "gui" (the default) — leave them to the DSH Web GUI for a person to answer.

• "deny" — set the session's policy to never: every subsequent request resolves as rejected without prompting. For unattended work this beats waiting forever — a clean failure instead of a hang.

• "auto-approve" — this plugin answers the request itself with a one-shot grant. Whether that is even possible is deployment-dependent: the plugin has to sit upstream of the GUI's answerer. Registering the mode is therefore not proof that it works — check the bridge's /dsh-bridge/diagnostics (approvalListener.listenerHits); the endpoint reports effective: false with a warning when it cannot. On the deployment this was built against, listenerHits is 0, so only deny and gui take effect there.

A tool call that has simply not finished yet is not reported as waiting; such a session stays running and carries an informational pendingTool field.

Security

The bridge is a control surface: whoever can reach it can send instructions to, and read the history of, every session in that DSH instance.

• It serves loopback callers only and answers 403 to anything else. This matters because the shipped Web profile binds 0.0.0.0.

• Set DSH_BRIDGE_TOKEN on both sides to additionally require an x-dsh-bridge-token header.

• The route is registered directly on DSH's HTTP server, so it is not covered by the /api trusted-host fence. Its own checks above are the only gate.

Limitations

• The MCP server and DSH must run on the same machine, because the bridge is loopback-only.

• One delegated turn is bounded by DSH_BRIDGE_TIMEOUT_MS; there is no streaming of partial output.

• cancel stops the active turn only — messages already queued in DSH keep running.

• The plugin reads a session's tail through sessionController.page, so a very large session reports its recent history rather than all of it.

Development

The plugin can be developed without restarting DSH: load it as a dynamic Cordis plugin first, verify behaviour against the live services, then install it as a bundle package. Do finish with one real restart — dynamic plugins are activated only after the services they need already exist, so they cannot catch a startup-order bug such as a missing inject.

License

MIT