deepseek-harness/packages/core/tools/README.md

# dsh-tools

Tool registry and execution pipeline. Tool plugins register their schemas and executors; the agent loop executes each call through `tools/pre-execute` (the allow/deny gate) → core dispatch → `tools/post-execute` (inspect/replace the result, attach context).

## Service: `ToolRegistry` (ctx key: `tools`)

### Public API

- `ctx.tools.register(definition: ToolDefinition): () => void` Register a tool. Disposed with the calling fiber.
- `ctx.tools.get(name: string): ToolDefinition | undefined`
- `ctx.tools.schemas(): ToolSchema[]` Schemas of all registered tools (without the `execute` functions). The shipped tools' schemas are catalogued in [docs/tool-catalog/tools.md](../../../docs/tool-catalog/tools.md), generated by booting each tool plugin and harvesting this method (see [the tool-schema-catalog RFC](../../../docs/rfc/implemented/process/2026-07-02-tool-schema-catalog.md)).
- `ctx.tools.execute(exec: ToolExecution): Promise<ToolExecutionResult>` Execute one tool call through the `tools/pre-execute` → dispatch → `tools/post-execute` pipeline.

### Injected services

`SystemPrompt` — the registry automatically feeds its tool schemas into the system-prompt assembly via `ctx.systemPrompt.tools()`.

### Events

| Event | Mode | Purpose |
|---|---|---|
| `tools/pre-execute` | waterfall | Allow/deny gate BEFORE a tool runs (sandbox, permission, hooks); returns `PreToolDecision` |
| `tools/post-execute` | waterfall | Inspect/replace the result AFTER a tool runs, attach context; returns `PostToolDecision` |
| `tools/change` | emit | A tool was registered or unregistered |

### Key types

- `ToolDefinition` — `ToolSchema` + `execute(args, exec): Promise<ContentBlock[] | { content: ContentBlock[]; meta? }>` (the bare array is the model-facing content; the object form additionally attaches an opaque, JSON-serializable `meta` presentation payload persisted on the `tool/result` event and handed back to `presentResult`), plus optional `presentCall(args)` / `presentResult(args, result)` for tool-owned UI presentation (see below).
- `ToolExecution` — one pending tool call: `{ callId, name, arguments, agent?, signal? }`.
- `ToolExecutionResult` — outcome: `{ callId, content, isError, error?, additionalContext?, meta? }`. On failure with a `HarnessError`, `error: { name, code }` carries the structured failure class alongside the model-facing text (the loop forwards it onto the `tool/result` session event for retry/sandbox plugins and replay). `additionalContext` (a `HookContext`) ferries any `tools/post-execute` context up to the loop, which buffers it and appends it as a `context/message` after all `tool/result`s in the step. `meta` is the tool's opaque presentation payload from a successful `execute` (the object return form); the loop forwards it onto the `tool/result` session event for result-card rendering.
- `PreToolDecision` — `{kind:'allow'}` | `{kind:'deny', reason}` | `{kind:'ask', reason?}`. Input rewrite (changing `arguments`) is deliberately NOT offered (it would desync the pre-execution audit/history/UI from what ran — its own proposed RFC); `ask` degrades to `deny` until the permission system lands.
- `PostToolDecision` — `{kind:'accept', content?, additionalContext?}` (keep the call successful, optionally replacing the model-facing content) | `{kind:'block', feedback, additionalContext?}` (turn it into an `isError` whose content is the corrective feedback). Output replacement is clean because `tool/result` is logged AFTER `execute()` returns.
- `ToolCallView` / `ToolResultView` — provider-neutral `card`-tagged render intents a tool returns from `presentCall` / `presentResult` to own how a UI renders ITS calls (see "Tool-owned UI presentation").

### Extension points

- Tool plugins call `ctx.tools.register()` — schemas flow into the assembly automatically.
- `tools/pre-execute` is the allow/deny gate (sandbox, permission, hooks): listeners receive `(exec, next)` and call `next()` to delegate to the default (allow) or return a `PreToolDecision` to short-circuit; a `deny`/`ask` skips dispatch and yields an `isError` result. `tools/post-execute` is the inspect/transform seam: `(exec, result, next)` → a `PostToolDecision` that can replace content, block with feedback, or attach `additionalContext`. Core dispatch sits between them as plain code; the tool body keeps its own try/catch so a thrown tool still reaches `post-execute` as an `isError`. Both follow the typed-Decision idiom shared with the `agent/*` interception seams (see [`dsh-agent`](../agent/README.md)).
- MCP servers: one plugin per server, discover tools, call `ctx.tools.register()` with the server's schemas.

### Typed tool parameter schemas

First-party plugin authors can use the `defineTool()` helper (exported from this package) for typed tool parameter schemas:

```ts
import { readFile } from 'node:fs/promises'
import type { Context } from 'cordis'
import { defineTool } from '@deepseek-ai/dsh-tools'

declare const ctx: Context

ctx.tools.register(defineTool({
  name: 'read_file',
  description: 'Read a file from disk.',
  parameters: {
    path: { type: 'string', required: true, description: 'Absolute file path' },
    offset: { type: 'number' },
    limit: { type: 'number' },
  },
  async execute(args, exec) {
    // args is typed: { path: string; offset?: number; limit?: number }
    const text = await readFile(args.path, 'utf8')
    return [{ type: 'text', text }]
  },
}))
```

The helper converts the author-facing `SchemaSpec` (with `required: true` as a per-property boolean) to standard JSON Schema for the wire format. Raw JSON-Schema tool definitions (from MCP servers) are still accepted by the registry directly.

A `defineTool` tool also **validates the model-generated arguments against its `SchemaSpec` before `execute` runs** (`validateArgs`). The model's JSON is untrusted — `InferArgs<S>` is a compile-time claim, not a runtime guarantee — so on a mismatch (missing required key, wrong primitive, bad enum member, nested violation) the tool throws a `ToolArgsError` (`code: 'INVALID_ARGS'`); the registry turns it into an `isError` result whose text lists the violations, which the model sees and self-corrects from. Validation mirrors the JSON Schema conversion exactly: extra keys are allowed, `default` is not applied, and an `object`/`array` prop without `properties`/`items` only type-checks. Raw-registered tools (MCP) are **not** validated by the harness — they validate their own input.

See `defineTool`, `validateArgs`, `ToolArgsError`, `SchemaSpec`, `InferArgs`, and `schemaSpecToJsonSchema` in the public API for details.

### Tool-owned UI presentation

A tool owns how ITS calls render in a UI (an editor's tool-call card, a CLI log line) — a UI plugin must NOT special-case tool names. A `ToolDefinition` may declare two optional, pure, display-only methods that return a **`card`-tagged render intent** (a discriminated union — a tool declares its card kind once and a UI bridge switches on `card`):

- `presentCall(args): ToolCallView | undefined` — the PENDING state, one of:
  - `{ card: 'generic', title, kind?, rawInput?, content?, locations? }` — the default card: a human-readable `title`, an optional `kind` (`read`/`edit`/`execute`/… for icon/treatment, default `other`), an optional `rawInput` (the salient input to show in a detail view — e.g. a background task id, NOT the whole args object), optional `content` (extra UI content blocks), and optional `locations` (`{ path, line? }[]` — files this call reads/modifies, so a capable UI can follow along; the ACP bridge forwards them as `tool_call.locations`).
  - `{ card: 'terminal', title, description?, cwd? }` — a shell command: a capable UI renders a terminal card (the `title` is the command, `description` renders above it, `cwd` heads it); an incapable UI falls back to a generic execute card.
  - `{ card: 'diff', title, diffs, locations? }` — a file create/modify: a capable UI renders an inline diff card from `diffs` (`{ path, oldText, newText }[]`; `oldText: null` for a new file). Used by `write`/`edit`.
- `presentResult(args, result): ToolResultView | undefined` — the COMPLETED state, given the same `args` and the `{ content, isError, meta? }` result, one of:
  - `{ card: 'generic', title?, content? }` — an optional replacement `title` and reformatted `content`.
  - `{ card: 'terminal', title?, output?, exitCode?, signal? }` — a terminal run's captured `output` and exit status. A capable UI shows an exit-status pill; an incapable UI gets a fenced ` ```console ` fallback the BRIDGE derives from `output` (the tool does not encode the fences).
  - `{ card: 'diff', title?, diffs }` — a completed file mutation as an inline diff. `diffs` is `FileDiff[]` — typically the applied hunks with surrounding context computed from the before/after content, or a whole-file diff (`oldText: null`) when there is no before-image (a file create). Used by `write`/`edit`; a `tool_call_update.content` replaces the call's content, so a mutation tool returns this even when it duplicates the call-time snippet (else the result text would clobber the pending diff).

Returning `undefined` (or omitting a method) tells a UI to fall back to a generic presentation (title = tool name, raw args as input, raw result content). Both methods must be **pure and side-effect-free**: a UI may call them during live streaming AND during a session-log replay, so they depend only on their arguments. `result.meta` is the tool's own optional presentation payload (opaque `unknown`, JSON-serializable), attached by `execute` (see below) and persisted on the `tool/result` event, so a `presentResult` reading it stays replay-deterministic (the same `meta` is read back from the log). With `defineTool`, `args` is the typed `InferArgs<S>` shape; the helper soft-validates before calling (a malformed/older logged arg shape yields `undefined` rather than throwing, since display must never crash a replay). The views are provider-neutral — the ACP bridge (`dsh-acp`) maps each `card` to ACP `tool_call`/`tool_call_update` wire fields (a `diff` card to a `{ type: 'diff' }` content block, a `terminal` card to the `_meta` terminal convention), and relativizes a file card's title against the session cwd. See the render-intent-union RFC (`docs/rfc/implemented/architecture/2026-07-02-tool-render-intent-union.md`) and the applied-hunk-diffs RFC (`docs/rfc/implemented/architecture/2026-07-02-result-time-applied-hunk-diffs.md`); `dsh-tool-bash` (terminal) and `dsh-tool-fs` (diff/generic) are the reference implementations.

```ts
import { defineTool } from '@deepseek-ai/dsh-tools'

const bash = defineTool({
  name: 'bash',
  description: 'Run a shell command.',
  parameters: {
    command: { type: 'string', required: true, description: 'The command to run.' },
    description: { type: 'string', required: true, description: 'One-line summary shown in the UI.' },
  },
  async execute(args) {
    return [{ type: 'text', text: `ran: ${args.command}` }]
  },
  // A terminal card: the command is the title, the description renders above it.
  presentCall: args => ({ card: 'terminal', title: args.command, description: args.description }),
  // A terminal result: the raw output + exit; the bridge derives the fenced fallback.
  presentResult: (_args, result) => {
    const block = result.content.length === 1 ? result.content[0] : undefined
    if (block === undefined || block.type !== 'text') return undefined
    return { card: 'terminal', output: block.text }
  },
})
```

### What is NOT here (TODO)

- **Tool shapes review** — when real tools land (e.g. a concurrency-safety hint for parallel execution); phase 1 executes tool calls sequentially.
- **Parallel execution** — the loop currently iterates tool calls sequentially.