dsh-custom-mode

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A custom mode for DeepSeek Harness (dsh). Its system prompt is a plain file you can edit on the Web settings page, and an edit takes effect on the next model step — no restart, no new session.

In one line: a settings page for dsh agent modes — choose a mode's base composition, toggle the plugin rows it mounts, and edit its system prompt, which the agent loop re-reads before every model step. Several modes ("assistants") can live side by side, each with its own prompt.

Also searched for as: custom mode · custom prompt · system-prompt editor · multi-mode / several assistants.

The four official modes (standard / ptc / minimal / cordis) are untouched.

The assistant manager, cropped to its own section (captured on a real instance by tools/screenshots/run-shots.sh; tools/browser-verify.mjs is what checks the page):

Install

One command installs everything — the settings-page plugin, and the preset it seeds on first activation:

dsh plugin --profile web add dsh-custom-mode@1.7.0   # pin the version to get this one for sure
# A bare `add dsh-custom-mode` is subject to pnpm's release cooldown (`minimumReleaseAge`, 1 day by
# default): for hours after a release it can silently install an OLDER version — measured: a bare
# install 38 minutes after 1.3.0 shipped landed on 1.0.3. Check what you got with `npm ls
# dsh-custom-mode` inside the profile, or pin the version as above.

Restart dsh afterwards, then choose「自定义模式」for a new session. The preset is written to $DSH_HOME/.agent-presets/custom/; anything already there is left alone, so a prompt.md you wrote yourself is never overwritten.

Platforms: the suite runs on every push under Ubuntu (Node 20 and 24) and Windows (Node 24) — the Windows job exists because that platform has its own failure modes (MSYS paths in install.sh, rename locking under concurrent saves, platform expressions evaluating the other way). Both shell scripts work in any POSIX shell, Git Bash included.

Installing from the interface (no terminal)

From dsh 0.1.6-alpha.2 there is a Plugins page: sidebar → Plugins → Add plugin. It takes three kinds of input, and all three work here:

Input	What to paste
Package name	dsh-custom-mode
GitHub repository URL	https://github.com/BOWLUNA/dsh-custom-mode (the repository root)
Local plugin directory	<your clone>/editor — note editor/, not the repository root

They work because the repository's root package.json declares dsh.bundle, main and exports["./client"] pointing into editor/. The root and editor/package.json must describe one plugin, so test/manifests.test.mjs asserts they agree on name, version and every declared path — two manifests describing one thing is a drift hazard, and a test is cheaper than remembering.

To keep the sources around as well — or to install without npm — clone and run the script, which does the same two things explicitly:

git clone https://github.com/BOWLUNA/dsh-custom-mode
cd dsh-custom-mode
./install.sh            # copies preset/ into $DSH_HOME/.agent-presets/custom/ and installs the plugin
./uninstall.sh          # removes the plugin; keeps your prompt unless you pass --purge

The mode needs a profile that ships agent-presets — the web profile does, tui and headless do not.

Usage

The settings page (Settings → "Custom mode") is an assistant manager: the top of the page lists every custom mode you have — create, switch, delete — and the four blocks below (name, base mode, plugin switches, system prompt) edit whichever one is selected.

• Ordering — "Move up / Move down" writes the order into each assistant's preset.yml (order, the roster's own sort key), so it survives a restart and the new-session picker follows it.
• Import / export a prompt — "Export prompt" saves the current text as a .md; "Import prompt" reads a file into the editor (nothing is written until you save), so an import goes through the same {{…}} validation as anything typed.
• Asking the agent to change its own prompt requires your approval. The in-session custom_prompt tool goes through the platform's approval seam (tools/pre-execute returning ask), so the request waits for an explicit「允许一次」and shows what would be written and where. Measured: with the ask approval policy the panel appears and approving really writes; with never (full access) nothing prompts and the call is denied. The worst case is therefore "the change does not happen", never "it happened quietly".
• 配置了却不生效会被点名 — the page warns when a setting cannot take effect: the「身份（系统提示词）」 row is off while prompt.md still has content (so your prompt is silently ignored), the custom_prompt tool row is off, the assistant has no name or no description (the picker shows the bare id /「暂无描述」).
• The agent can change its own prompt, with your approval — the in-session custom_prompt tool reads the prompt, replaces it, or appends to it. Appending matters because it never has to reproduce the whole prompt: an agent that wants to remember one rule cannot lose existing content on the way (measured: it may still read first to see what it is adding to). Both writing actions go through the platform's approval panel first.
• Change history — every save, and any change made outside this page (the in-session custom_prompt tool, a hand edit of prompt.md), leaves a version in the history list under the prompt box, labelled with when and where it came from. Loading one only edits the draft: nothing is written until you save, so browsing old versions cannot destroy the current one. Before this, a prompt changed from inside a session was invisible — the page only ever showed "the current text".
• Reset to the factory prompt — one click puts the shipped template (the text a new assistant starts from) back into the editor. It is draft-only like every other edit: nothing is written until you save, and Reload discards it. Before this existed, a prompt you had edited into a corner could only be recovered by deleting the assistant and creating it again.
• New assistant — type a name and click "New assistant". It is seeded from the packaged template: the full Standard row set plus a starter prompt, selectable in a new session as soon as you save it — in an already-open page the picker's list is a load-time snapshot, so refresh (F5) once to see a new assistant there (measured; the roster itself is up to date).
• Duplicate — copies the selected assistant's prompt, base mode and row switches into a new one; the two are independent afterwards.
• Each assistant is independent — its prompt, base mode and row switches are its own; changing one leaves the others alone.
• Base mode is the row set, not the prompt — it decides which rows exist and which tools the mode has; this plugin always replaces the base's persona row with its own reader (complete: false), so the base's prompt semantics are not inherited. Minimal is the visible case: you get minimal's tool set, not minimal's prompt.
• Switching assistants never discards drafts — each keeps its own unsaved edits, marked "Unsaved" in the list; the only path that throws edits away is the reload button, which renames itself to say so.
• Delete — the shell's own risk-confirmation dialog, which requires ticking an acknowledgement. Deletion only removes the mode directory from disk: sessions already using it keep running (their composition was read when they started), and new sessions no longer offer it.
• Ask the agent — every assistant ships a custom_prompt tool, so a session can read or rewrite its own prompt.
• Edit the file — $DSH_HOME/.agent-presets/<assistant id>/prompt.md is that assistant's single source of truth.

Only {{model}}, {{cwd}} and {{provider}} are interpolated. An unknown {{…}} is rejected when saved: the renderer throws on it, which would fail every request in that mode.

Every control (buttons, inputs, switches, tags, the confirmation dialog, icons) comes from the shell's own @deepseek-ai/dsh-client-ui-primitives, so theme, light/dark and future restyling reach this page automatically; a shell that does not provide those atoms falls back to built-in plain controls with the same behaviour.

An "assistant" is one directory under the user preset root (default $DSH_HOME/.agent-presets/), and its directory name is its internal id. The page manages only presets this tool created — the test is that the directory carries prompt.md and that its composition injects identity through prompt-reader.mjs. Any other hand-authored preset is neither listed nor touched: the page regenerates a composition from a base mode, and doing that to a hand-written one would destroy it.

How this differs from the built-in Plugins page

From dsh 0.1.6-alpha.2 the harness ships a Plugins page that can enable and disable plugins live. It and this mode's per-row switches act at different levels:

	Built-in Plugins page	This mode's per-row switches
Scope	The whole profile — what this machine has installed	One agent mode — which rows its composition mounts
Typical use	Turn a plugin off globally	Keep Standard fully loaded and trim this mode to what it needs

They coexist: the harness decides what the machine has, this mode decides which of it the mode uses.

The boundary is drawn by upstream: the Plugins page documents that it manages "the profile's bundles and their uniquely addressable rows", and states plainly that agent-preset rows remain read-only. The preset layer is therefore out of its reach — and that is exactly the layer this mode covers.

A demonstrable example: tool-plugin-manager (the agent-facing install/toggle tool) ships off in Standard and PTC — only Creator enables it. The official modes give you no way to change that; here you flip one switch.

How it works

dsh normally takes the system prompt from a preset's YAML, and @deepseek-ai/dsh-persona resolves its prefix once at mount. This preset registers the same deployment:persona-prefix section but makes its text a function, which the agent loop calls before every model step.

Two different things therefore decide when a change lands:

• Prompt text is re-read per step, so an edit applies to the running session immediately.
• Switches and base mode rewrite the composition file. agent-presets remounts a preset when that file's mtimeMs and size change, so a new session picks them up; a running session keeps the configuration it started with, which is deliberate — swapping a tool set mid-conversation would be wrong.

Row switches are tri-state. A row you never touched stays byte-identical to the shipped one, including its !!js platform condition and its shipped disabled state; an explicit on/off replaces that condition with a boolean. Platform expressions are evaluated on the host, so the page shows the state actually in force on this machine rather than whether a key exists.

Several assistants need no new mechanism: dsh-agent-presets already scans every directory under the user preset root, and re-reads those roots on each roster call, so a directory created just now is selectable the next time a session is started. Each assistant's prompt-reader.mjs / prompt-tool.mjs resolves prompt.md relative to its own module location, so N copies are N independent prompts. Creation seeds the packaged template; deletion goes through the platform's agentPresets.remove(), which refuses a shipped preset and re-checks that the directory really lives under the writable root.

Versioning

The package version is its own line — 1.0.0, then 1.0.1, … It does not mirror the DSH release. What this plugin supports is declared in engines.dsh and the @deepseek-ai/dsh peer range in editor/package.json, and tools/verify-version-consistency.mjs (run in CI) asserts that the DSH version CI installs and tests falls inside those ranges.

Both dsh lines are supported: the latest stable (0.1.5-rc.2) and the latest preview (0.1.6-alpha.2) — declared as >=0.1.5-rc.2 <0.2.0-0, and CI installs both lines and runs the whole suite against each. Measured on 0.1.5-rc.2: install, composition tree, the /api fence, state/history/warnings and the 38 browser checks all pass; tools/pre-execute (the approval seam) and connection.fetch.register (the fenced route channel) both exist there too.

Two reasons for the split. A bare x.y.z is what directories and markets require before they will auto-install a package — several resolve npm latest and reject anything carrying a prerelease tag. And a version string was never a checkable claim anyway: the declared range is, and it is the thing that goes stale when upstream moves. What decides compatibility in practice is still whether the APIs below exist, which is what the ranges are for.

Coupling points (check these when upgrading dsh)

Dependency	Failure if it changes
ctx.systemPrompt.section() with a function text	the prompt stops hot-reloading — the point of the project
agentPresets remounts on composition mtimeMs+size	switches need a process restart to apply
ctx.tools.register()	loses the custom_prompt tool
ctx.connection.fetch.register({ path, methods, requestBody, fetch })	settings page 404s — nothing is registered
kind: 'prefix' matching both path and path/…	only the list opens; /state, /create, /delete all 404
agentPresets.list() rows carrying id / trust / path, with preset.yml supplying name / description	the assistant list is empty or unrecognisable
agentPresets.remove(id), refusing trust: 'system'	deletion fails (the page shows the platform's reason)
the /api channel's fence (Host/Origin + browser auth)	the page cannot authenticate at all; do not "fix" it by moving the route to the raw webServer table
ctx.inject(deps, cb) (scoped wait)	the row parks in pending in profiles without a web server
dsh.client + exports["./client"], client bundle id == package name	the browser half is not discovered
settings.section slot (id / order / label)	page placement and label
settings.section no longer takes locale: (since 0.1.6-alpha.2)	the shell does not hand over a t bound to this namespace; the page carries its own dictionaries as a floor — see ARCHITECTURE §15
preset.yml's order participating in the roster sort	move up/down stops working
ctx.locale.register/bind	falls back to Chinese
shipped layout <presets>/<id>/agent.cordis.yml and row text shape	base-mode switching breaks
!!js platform expressions	platform rows display the wrong state

Documentation

• docs/TROUBLESHOOTING.md — failures reproduced on a real machine, with symptoms, cause and a way out.
• docs/MEASUREMENTS.md — the commands and raw output behind each claim.
• docs/ARCHITECTURE.md — why this is two artifacts, and which host APIs it depends on.
• docs/PUBLISHING.md — how the npm package is published.
• AGENTS.md — agent-facing notes, including the full recipe for verifying the UI in a real browser on the lab (tools/browser-verify.mjs).
• CHANGELOG.md · SECURITY.md · CONTRIBUTING.md

Development

node test/run.mjs        # 13 suites; resolves the shipped presets itself

Edits to editor/client.js are hot-swapped by @deepseek-ai/dsh-client-hmr about a second later; the host half (index.mjs, composition.mjs, meta.mjs, paths.mjs) needs a restart. See test/README.md for what each suite protects, and CONTRIBUTING.md before changing behaviour.

License

MIT

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Built with

Model	DeepSeek V4.1 Flash (deepseek-v4-flash, provider deepseek-official)
Runtime	DeepSeek Harness 0.1.6-alpha.2 (@deepseek-ai/dsh, preview)
Uncached input	224,058 tok
Cache reads	125,638,016 tok
Output	425,539 tok

The whole project, research and dead ends included, cost the DSH client 126,287,613 tokens at a 99.8% cache hit rate (cache reads ÷ all input, 125,862,074).