dsh-mcp-relay
dsh-mcp-relay
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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 relay 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 relay replaces that with a small structured API: one tool call in, one result out.
Architecture
MCP client (stdio)
└── bin/dsh-mcp-relay.mjs MCP server; polls the relay, holds questions for the caller
└── HTTP 127.0.0.1:<port>/dsh-relay
└── 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-relay.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-relay
Then restart DSH. On startup the log should show:
[dsh-mcp-relay] mounted /dsh-relay (tokenRequired=false)
Verify it independently:
curl -s http://127.0.0.1:3080/dsh-relay/ping
# {"ok":true,"data":{"relay":"dsh-mcp-relay","version":"0.6.0","tokenRequired":false}}
If your instance listens on a port other than 3080, use that port here and set DSH_RELAY_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-relay": "github:Nigheart/dsh-mcp-relay" },
"dsh": { "profile": { "bundles": ["@deepseek-ai/dsh-base", "@deepseek-ai/dsh-web-app", "dsh-mcp-relay"] } }
}
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-relay/bin/dsh-mcp-relay.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_RELAY_URL = "http://127.0.0.1:8080/dsh-relay"
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:
| Variable | Default | Purpose |
|---|
DSH_RELAY_URL | http://127.0.0.1:3080/dsh-relay | Where the plugin listens. |
DSH_RELAY_TOKEN | (unset) | Sent as x-dsh-relay-token; must match the plugin's value. |
DSH_RELAY_TIMEOUT_MS | 600000 | Default wait for one delegated turn. |
DSH_RELAY_POLL_MS | 2000 | Progress poll interval. |
Tools
| Tool | Purpose |
|---|
dsh_list_sessions | List sessions of the running instance, optionally filtered to one workspace. |
dsh_models | List the provider/model ids this instance can route, with each model's reasoning efforts. |
dsh_delegate | Create a session in a workspace, or continue one by sessionId, send an instruction, and wait for that turn to finish. |
dsh_answer | Answer a question the DSH agent asked, so it can resume. |
dsh_approval | Choose how a session resolves future approval requests: gui, auto-approve, or deny. |
dsh_cancel | Cancel the active turn — the way out of an approval nobody can answer. |
dsh_poll | Read a session's status and latest output; use after a wait that returned waiting or timeout. |
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:
status | Meaning |
|---|
completed | The turn finished; output holds the agent's final answer. |
waiting | Blocked on a human: either a question takeover is holding for you, or an open approval request. |
timeout | Still running; call dsh_poll with the same baselineSeq. |
The relay also attaches every session it creates (or reuses) to the DSH workspace owning the target
directory. DSH groups sessions in its GUI by that explicit attachment rather than by working directory, so
without it a delegated session runs fine but shows up as ungrouped. Sessions created before this behaviour
existed can be repaired with one call to the relay's POST /dsh-relay/attach-all endpoint.
Choosing the model
A session runs on the instance's default model unless you say otherwise. dsh_models reports what this
instance can route right now — provider groups, model ids, and each model's reasoning efforts:
dsh_models()
dsh_delegate({ workspace: "/home/me/project", instruction: "…",
model: "deepseek-v4.1-pro", reasoningEffort: "high" })
model takes a model id; provider is inferred when that id is unambiguous, and provider/model is
always accepted. reasoningEffort must be one of the efforts dsh_models lists for that model. A route
this instance cannot serve fails the call before the instruction is sent, rather than quietly running
it on some other model.
The selection applies to this turn and is also saved as the instance default for sessions created
without one — the same stickiness DSH's own model picker has, so choose deliberately. Omit model to
leave the session on whatever it already uses. dsh_delegate echoes the selection it installed as
model (with modelNote); dsh_list_sessions and dsh_poll report each session's current model,
read from DSH's model-selection projection (a hint: it is null until the session has recorded a
request, and on deployments without that projection).
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 relay's /dsh-relay/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 relay 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_RELAY_TOKEN on both sides to additionally require an x-dsh-relay-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 relay is loopback-only.
- One delegated turn is bounded by
DSH_RELAY_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.
The relay's route table has a dependency-free test that stubs the Cordis context, so it needs neither DSH nor
a restart:
npm test
License
MIT
