dsh-prompt-armor

Give each model its own system prompt in DeepSeek Harness.

A profile is a named prompt plus the model patterns it applies to. When an agent assembles its system prompt, the profile that matches the current model is injected. Different models therefore get different instructions, from the same harness, with no restart and no core-file patching.

Why this exists

The community plugin dsh-purge does the same job — inject a prompt into every model — by rewriting the files inside @deepseek-ai/* with a 355 KB table of string replacements. That approach has three consequences:

• It is version-fragile. The table matches literal source strings, so a Harness release that moves a space silently breaks the plugin. The table needs a new branch for every release.
• It is undone by the package manager. The patches live in node_modules, so a reinstall wipes them and the plugin has to re-patch on the next start.
• It has to guess. The official workspace baseline is a user message, not a prompt section, so the plugin's "drop the baseline" filter matches by name and text and usually does not fire.

This plugin uses the official seam instead. The Harness exposes ctx.systemPrompt.section() for exactly this purpose, and the harness itself uses it for every tool's guidance text. The section is registered on the plugin's own context, so unloading the plugin removes it and the system prompt returns to its default shape.

It also implements a thing dsh-purge only advertises: per-model dispatch. The upstream README says "swap prompts per model", but its code has no model, provider, or route key anywhere — the prompt it injects is the same for every model. Here the model id is read from the assembly context, so the dispatch is real.

Install

dsh plugin --profile desktop add <path-to-this-directory>

Or, in the desktop client, use Settings → Plugins, and enter the directory in the install box.

Use

Open Settings → Model Prompts. The panel lists the profiles on the left and edits the selected one on the right.

Field	Meaning
Name	The label shown in the panel and, optionally, above the injected text.
Applies to	Model patterns, one per line. * is a wildcard.
Enabled	Whether the profile contributes at all.
Prompt	The text injected into the system prompt.

Two variables are substituted in the prompt body: {{model}} and {{provider}}. Any other {{…}} is left exactly as written.

Matching

The most specific pattern wins:

• an exact model id beats a wildcard;
• a longer wildcard beats a shorter one;
• a disabled profile never applies;
• with no match, nothing is injected and the system prompt is unchanged.

So a profile listing deepseek-v4.1-flash applies to that model only, while a profile listing deepseek-* applies to every DeepSeek model, and a profile listing * is the catch-all.

Files

The Host owns the rules on disk, under $DSH_HOME/prompt-armor/:

index.json          the profile list and their model patterns
profiles/<id>.md    one profile's prompt text

The panel writes through the Host, but the files are ordinary text: edit them in any editor and a running agent picks the change up on its next step.

Configuration

The plugin's row in cordis.patch.yml accepts:

Key	Default	Meaning
enabled	true	Whether the plugin contributes a section at all.
dataDir	$DSH_HOME/prompt-armor	Where the profiles live.
order	-100000	Where the injected text sits in the prompt.
showProfileName	true	Whether the profile name heads the injected text.

order is a plain number, so it does not depend on a named slot that a future release may renumber. The default puts the injected text first, ahead of the harness' own identity line, so a persona reads as the frame rather than as an aside. A value above 10200 places it after the deployment persona suffix instead, where it reads as a trailing instruction.

How it works

The Host half registers one prompt section:

ctx.systemPrompt.section({
  name: 'dsh-prompt-armor:profile',
  order: config.order,
  interpolate: false,
  text: (context) => {
    const model = context.agent?.options?.model
    const profile = selectProfile(store.profiles, model)
    return profile === null ? '' : store.text(profile.id)
  },
})

text is a function, so it is evaluated at every prompt assembly and can read the model the assembly is for. The section is registered with interpolate: false, because a user prompt may legitimately contain {{…}} and the harness throws on an unknown variable reference.

The browser half is plain JavaScript with no build step: it registers a settings.section entry and talks to the Host over a small JSON route on the harness' own web server. Mutating requests carry a custom header, so a cross-origin page cannot drive them.

Tests

node test/rules.test.mjs       # the matcher and the store
DSH_ASAR=<resources>/app.asar node test/integration.test.mjs

The integration test extracts the installed @deepseek-ai/dsh-system-prompt from the desktop app.asar, mounts the Host half on the real registry, and asserts the assembled prompt — so "the injected text reaches the model" is checked against the harness that is actually installed.

Licence

MIT.