deepseek-harness/docs/subsystems/system-prompt.md

# System Prompt Assembly

English | [中文](system-prompt.zh.md)

The [system-prompt package](../../packages/core/system-prompt) owns the data exchanged between prompt contributors and one assembly call. The package [README](../../packages/core/system-prompt/README.md) documents registration, ordering, scoping, and rendering behavior; this page records the exact cross-package types that plugins implement or pass.

Source: [`packages/core/system-prompt/src/index.ts`](../../packages/core/system-prompt/src/index.ts).

## Assembly context

`AssembleContext` identifies the scope layer one assembly resolves and may carry the explicit control signal for that request. It is merge-extensible: `dsh-agent` adds the optional live `agent` field, and `assembleContextFor(agent, signal)` sets the explicit fields together. A bare assembly has neither scope nor signal.

```ts type-equiv
/** Merge-extensible context for one prompt assembly. */
interface AssembleContext {
  /**
   * Scope whose providers and waterfall listeners participate. When absent,
   * only global providers and subject-less listeners participate.
   */
  scope?: ScopeKey
  /** Explicit control signal for the turn that requested this assembly, when any. */
  signal?: AbortSignal
}
```

## Tool-provider result

`ToolProviderResult.schemas` is the model-visible set for the current assembly. `knownNames` is the provider's pre-restriction name universe used to distinguish a configured-name typo from a known tool that is deliberately hidden in this scope.

```ts type-equiv
/** Tool schemas visible in one assembly and their pre-restriction name set. */
interface ToolProviderResult {
  /** The schemas this provider contributes to THIS assembly. */
  readonly schemas: readonly ToolSchema[]
  /** The pre-restriction name universe for config validation (defaults to `schemas`' names). */
  readonly knownNames?: readonly string[]
}
```

## Prompt sections

`PromptSection` is a readonly same-process registration contract. Its text may be static or resolved from the current assembly context.

```ts type-equiv
/** One contributed section of the system prompt (registry input). */
interface PromptSection {
  /** Unique name — a duplicate registration throws (see {@link SystemPrompt.section}). */
  readonly name: string
  /**
   * Sections are concatenated in ascending order. Convention: `-100` is the
   * harness identity, `0` the deployment persona, tool guidance uses 100–199;
   * other negative orders also render before the persona.
   */
  readonly order: number
  /**
   * Static text or a provider evaluated at each assembly with that assembly's
   * {@link AssembleContext}. The text may reference `{{variable}}`s — they are
   * interpolated later, by {@link renderPrompt}.
   */
  readonly text: string | ((context: AssembleContext) => string)
}
```

## Dynamic prompt context

`PromptContext` is the cache-safe counterpart to `PromptSection`. The assembly resolves and orders these contributions, while agent-loop logs their complete current snapshot after retained model history only when it changed or compaction removed it.

```ts type-equiv
/** Dynamic model context materialized as a durable user-role snapshot. */
interface PromptContext {
  /** Unique name — a duplicate registration throws (see {@link SystemPrompt.context}). */
  readonly name: string
  /** Contexts are joined in ascending order. */
  readonly order: number
  /** Static text or a provider evaluated for each assembly. Empty text contributes nothing. */
  readonly text: string | ((context: AssembleContext) => string)
}
```

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## Cordis surface

Generated from source by `scripts/gen-cordis-catalog.ts` (verified fresh by `pnpm run verify-cordis-catalog` in doc-sync; regenerate with `pnpm run gen-cordis-catalog`) — this section is byte-identical in both language sides of the page. Signature blocks use a `ts cordis-catalog` fence and keep the original source JSDoc; dispatch modes are defined in the [primer](../cordis-primer.md#dispatch-modes), and the framework-inherited `ctx` surface lives in [cordis-api/inherited.md](../cordis-api/inherited.md).

<a id="ctxsystemprompt--systemprompt"></a>

### `ctx.systemPrompt` — `SystemPrompt`

Registry service for the prompt inputs assembled before each model step.

```ts cordis-catalog
/**
 * Register an ordered prompt section in the calling context's scope. A scoped
 * section shadows a global section with the same name; duplicates within one
 * layer and non-finite orders throw. Registration and disposal emit
 * `system-prompt/change`.
 * @param section - the section to register.
 * @returns the exact Cordis effect disposer.
 */
section(section: PromptSection): () => void

/**
 * Register ordered dynamic context in the calling context's scope. Scoped
 * entries shadow global entries with the same name.
 * @param context - the context contribution to register.
 * @returns the exact Cordis effect disposer.
 */
context(context: PromptContext): () => void

/**
 * Register a tool-schema provider in the calling context's scope. Global and
 * matching scoped providers both contribute; returning the reserved
 * {@link TOOL_ORDER_REST} name makes assembly fail.
 * @param provider - evaluated for each assembly with its context.
 * @returns the exact Cordis effect disposer.
 */
tools(provider: (context: AssembleContext) => ToolProviderResult): () => void

/**
 * Register a prompt variable in the calling context's scope. Scoped values
 * shadow globals; invalid or duplicate names throw. A provider may return
 * `undefined`, but rendering a section that references that value then fails.
 * @param name - the `[a-z][a-z0-9_]*` reference name.
 * @param provider - evaluated for each assembly.
 * @returns the exact Cordis effect disposer.
 */
variable(name: string, provider: (context: AssembleContext) => string | undefined): () => void

/**
 * Assemble global and scoped providers, detach tool parameters, apply
 * canonical ordering, then run the assembly waterfall. Scoped sections and
 * variables shadow globals; the returned waterfall value is authoritative.
 * @param context - the optional scope and plugin-defined assembly fields.
 * @returns the authoritative post-waterfall assembly.
 */
async assemble(context: AssembleContext = {}): Promise<PromptAssembly>
```

Source: [`packages/core/system-prompt/src/index.ts:325`](../../packages/core/system-prompt/src/index.ts)

<a id="system-prompt-events"></a>

### `system-prompt/*` events

<a id="system-promptassemble--waterfall"></a>

#### `system-prompt/assemble` — waterfall

Expert waterfall over the assembled sections, contexts, tools, and variables. Scope-filtered dispatch (`@deepseek-ai/dsh-scope`): scoped listeners receive only that scope's assemblies. The returned value is authoritative. A supplied signal controls only this explicit assembly request and must not be retained to control later turns.

```ts cordis-catalog
/**
 * Expert waterfall over the assembled sections, contexts, tools, and variables.
 * Scope-filtered dispatch (`@deepseek-ai/dsh-scope`): scoped listeners
 * receive only that scope's assemblies. The returned value is authoritative.
 * A supplied signal controls only this explicit assembly request and must not
 * be retained to control later turns.
 * @param assembly - the mutable assembly built from registered providers.
 * @param context - the caller's per-assembly context.
 * @mode waterfall
 */
'system-prompt/assemble'(this: Scoped<SystemPrompt>, assembly: PromptAssembly, context: AssembleContext, next: () => Promise<PromptAssembly>): Promise<PromptAssembly>
```

Types: [Scoped](scope.md)

Source: [`packages/core/system-prompt/src/index.ts:29`](../../packages/core/system-prompt/src/index.ts)

<a id="system-promptchange--emit"></a>

#### `system-prompt/change` — emit

Emitted when any prompt provider changes. This registry notification is unfiltered because a global change affects every scope.

```ts cordis-catalog
/**
 * Emitted when any prompt provider changes. This registry notification is
 * unfiltered because a global change affects every scope.
 * @mode emit
 */
'system-prompt/change'(): void
```

Source: [`packages/core/system-prompt/src/index.ts:35`](../../packages/core/system-prompt/src/index.ts)
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