# 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 extensible allow/deny gate) → monotonic registered guards → `tools/execute` (an around-dispatch wrapper for timeout/retry/metrics plugins) → `tools/post-execute` (inspect/replace the result, attach context) → the observe-only `tools/result` notification. The registry also owns HOW its tools are presented to the model — its `mode` config selects native function calling, [Code Mode](#code-mode), or both.

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

### Config

```yaml
tools:
  mode: native   # native (default) | code | both
```

`native` contributes the calling agent's visible end capabilities as wire function definitions. Under `code`, this registry's canonical contribution is the reserved `run_code` transport plus the generated `tools:sdk` prompt section (see [Code Mode](#code-mode)); an assembly listener may still deliberately add unrelated schemas. `both` contributes the visible native definitions, `run_code`, and the SDK section. In non-native modes both infrastructure pieces are protected rather than filterable capabilities: restrictions and assembly listeners cannot remove them, a scoped section cannot shadow the globally protected `tools:sdk`, and registering, shadowing, or explicitly filtering `run_code` fails loudly. Non-native modes require a loaded `ctx.codeRuntime` with `language: 'typescript'`; a missing or mismatched runtime rejects every prompt assembly with an actionable error, and a `systemPrompt.toolOrder` naming tools the mode no longer contributes rejects the assembly the same way.

### Public API

- `ctx.tools.register(definition: ToolDefinition): () => Promise<void> | void` Register a tool as a frozen snapshot. Parameters must survive lossless-JSON validation before and after cloning; scalar fields are copied, and execute/presentation callbacks are bound once to the original definition as their method receiver, so later callback-property replacement cannot change dispatch. The layer is the CALLING context's scope (`dsh-scope`): a plain plugin context registers globally; an agent's `agent.ctx` registers for that agent alone, SHADOWING a same-named global tool there (per-agent tool variants). Duplicate names within one layer throw; non-native modes also reject the reserved `run_code` transport name. Disposed with the calling fiber (= the agent, for scoped registrations).
- `ctx.tools.restrict(filter: ToolRestriction): () => Promise<void> | void` Scoped-only (throws on a plain context): mask the GLOBAL end-capability surface for the calling agent — `allow` keeps only the listed tools, `deny` removes them; multiple restrictions intersect; scoped registrations bypass restriction as explicit grants. The reserved `run_code` transport remains available automatically and cannot be named explicitly. Snapshot-at-registration, loud unknown-name validation, `restrict({})` rejects (the materialized-empty-config trap).
- `ctx.tools.get(name: string, scope?: ScopeKey): ToolDefinition | undefined` Resolution as one scope sees it (shadowing applied; a restricted-away global reads as absent) — presenters pass the calling agent so the card matches what executed. Returned definitions are the registry's frozen snapshots.
- `ctx.tools.visible(scope?: ScopeKey): ToolDefinition[]` The canonical executable view — restricted global layer ∪ the scope's own layer, plus the reserved transport in non-native modes — feeding prompt assembly, `get`, and `execute`, so presentation and dispatch resolve the same frozen definitions.
- `ctx.tools.knownNames(scope?: ScopeKey): string[]` The PRE-restriction end-capability name universe `restrict` validates against: a typo fails loud while a restricted-away tool stays a normal absence. Presentation providers add reserved transport names separately when validating `toolOrder`.
- `ctx.tools.schemas(scope?: ScopeKey): ToolSchema[]` Schemas of everything the scope can see (without the `execute` functions). The shipped tools' schemas are catalogued in [docs/tool-catalog.md](../../../docs/tool-catalog.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.guard(guard: ToolGuard): () => Promise<void> | void` Register a monotonic synchronous execution guard after `tools/pre-execute`: returning a reason denies the call, while `undefined` leaves it unchanged. A plain-context guard applies globally; an `agent.ctx` guard applies only to that agent. Later waterfall listeners cannot turn a guard denial back into permission. Disposed with the calling fiber.
- `ctx.tools.execute(exec: ToolExecutionInput): Promise<ToolExecutionResult>` Snapshot one single-use call input into a pipeline-owned execution, assign its opaque correlation token, require `arguments` to be losslessly JSON-serializable before and after cloning, deep-freeze the detached arguments, and protect its identity before running `tools/pre-execute` → guards → `tools/execute` → `tools/post-execute`; optional `signal` is the only operational field an around-dispatch wrapper may add, replace, or remove. Validate the final result as losslessly JSON-serializable and freeze the complete execution before `tools/result` observers run. Invalid or unstable input—including cloneable mutable exotics—and malformed or non-JSON listener/tool results normalize to `isError` outcomes rather than bypassing policy or failing later at the session log.

### Injected services

`SystemPrompt` — the registry automatically feeds its tool schemas into the system-prompt assembly via `ctx.systemPrompt.tools()`. The approval seam is consumed opportunistically instead (`ctx.get('approval')`, no static inject): a deployment without it keeps the ask→deny degrade, and the registry stays active either way.

### Live events

The live registry pipeline has three transformable waterfalls followed by the owner-final `tools/result` observation boundary; registry changes are deliberately unfiltered shared-state notifications. Exact signatures, dispatch modes, scope filtering, and failure-containment contracts live in the generated [Cordis event catalog](../../../docs/cordis-catalog/events.md), while the complete ordering is visualized in the generated [tool execution pipeline](../../../docs/tool-execution-pipeline.md). `tools/result` is live and observe-only; the similarly named `tool/result` is the durable session event the agent loop appends afterwards.

### 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). It also carries an optional cooperative timeout budget `timeoutMs?: number` (ms) enforced by `@deepseek-ai/dsh-timeout-policy`, never sent to the model. Registration stores a frozen snapshot with detached JSON parameters and once-bound callback identities.
- `ToolExecutionInput` — the caller-supplied call description: `{ callId, name, arguments, agent?, parent?, signal? }`; `arguments` must be losslessly JSON-serializable, and callers may pass an enclosing execution's opaque token as `parent` but never choose the new execution's own token.
- `ToolExecutionToken` — a frozen, property-free identity value assigned by the registry. It supports equality correlation only and exposes no live outer execution state.
- `ToolExecution` — the pipeline-owned call: immutable `{ token, callId, name, arguments, agent?, parent? }` identity plus optional operational `signal`, which an around wrapper may add, replace, remove, and restore. A nested call's `parent` is a `ToolExecutionToken`, not an execution object.
- `ToolExecutionResult` — losslessly JSON-serializable outcome: `{ callId, content, isError, error?, additionalContext?, meta? }`. The registry validates the complete post-policy value before final observation. 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?}`. The registry validates this exact union at runtime: a JavaScript/casted value with an unknown kind, a malformed reason, or extra fields fails closed as an `isError`; the tool body does not run and final observers still receive one result. 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` is serviced by [`ctx.approval`](../../ui/user-approval/README.md) when a deployment mounts it (`allowed-once` proceeds to dispatch; `rejected`/`cancelled`/`unavailable` deny with distinct reasons) and degrades to `deny` when none is mounted or the execution carries no agent.
- `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.
- `ToolGuard` — `(execution) => string | undefined`; the returned string is a final monotonic denial reason evaluated after the reorderable pre-execute waterfall and before dispatch.
- `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 reorderable allow/deny/ask 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` skips dispatch, while an `ask` resolves through the approval seam and dispatches only after a grant. Either non-grant path yields an `isError` result. `ctx.tools.guard()` installs scope-aware monotonic policy after that waterfall when a denial must not be overridable by listener ordering. `tools/execute` is the around-dispatch seam (timeout, retry, metrics): listeners receive `(exec, next)` and call `next()` to delegate to core dispatch (returning its `ToolExecutionResult`, optionally wrapped), or return a replacement result to short-circuit dispatch; the base `next()` is dispatch-with-normalization, so `await next()` already yields an `isError` result for a thrown or unknown tool. A wrapper may change only `exec.signal` before `next()`—adding a per-call deadline, replacing a caller signal, or restoring absence afterwards—because call identity is protected before policy begins. `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 is the base of the `tools/execute` waterfall; the tool body keeps its own error boundary so a thrown tool still reaches `post-execute` as an `isError`. Finally, `tools/result` observes the immutable authoritative result after every transform and error boundary. All follow the typed-decision idiom shared with the `agent/*` seams (see [`dsh-agent`](../agent/README.md)); `@deepseek-ai/dsh-timeout-policy` is the reference `tools/execute` wrapper.
- 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.

`defineTool` also validates an optional `timeoutMs` at definition time when present: it must be a positive finite number, or the helper throws — the budget is attached to the produced `ToolDefinition` (for `@deepseek-ai/dsh-timeout-policy`) and never reaches the model.

### Structured-output schema subset

A separate vocabulary for callers that DEMAND a machine-readable value from an agent — the subagent seam's `SubagentStartRequest.outputSchema` (and, by extension, a workflow's `agent({ schema })`). Unlike `SchemaSpec` (the author-facing DSL for tool parameters), a `StructuredOutputSchema` is an object-rooted **raw JSON Schema subset** as data: it travels verbatim to the model as a forced tool's `parameters`, and the produced value is validated against it.

The subset is deliberately narrow and REJECTS LOUD outside it — accepting a keyword the validator doesn't enforce would validate less than the schema promises (accepted-then-ignored). Supported: single-string `type` (`object`/`array`/`string`/`number`/`integer`/`boolean`/`null`; type arrays rejected), `properties`/`required`/`additionalProperties` (boolean; every `required` key must be declared), `items`, scalar-only `enum`/`const`; annotations (`description`/`title`/`default`/`examples`) are ignored but must still be JSON data. `assertSupportedOutputSchema(schema)` throws `OutputSchemaError` (`code: 'UNSUPPORTED_SCHEMA'`, listing every violation) for anything else; `validateStructuredValue(schema, value)` returns path-qualified violations (empty = valid, total — never throws).

### 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 }
  },
})
```

### Code Mode

Under `mode: code` (or `both`) the registry turns the tool surface into a programming API, per the [Code Mode RFC](../../../docs/rfc/implemented/feature/2026-06-15-code-mode.md): the model writes a TypeScript program (the body of an async function) and passes it to the reserved wire transport `run_code`; the program runs in `ctx.codeRuntime` (the [code-execution seam](../../code-runtime/README.md) — the shipped backend is a worker thread) with one async binding per visible end-capability tool (`await tools.bash({...})`), and ONLY what it prints or returns re-enters the model's context. Scope restrictions change those SDK bindings but cannot remove or replace the transport itself.

- **The SDK section** (`tools:sdk`, order 150): a lazy prompt section regenerating, at each assembly, a `declare const tools: {...}` TypeScript declaration of the calling scope's visible end capabilities (exotic names via quoted keys), plus fixed usage instructions. The registry protects this section and the `run_code` wire schema after the assembly waterfall, so Code Mode cannot silently lose either half of its transport. Deterministic — lexicographic tool order, byte-identical text for an unchanged tool set (prefix-cache-friendly). The codegen (`jsonSchemaToTs`, exported) is total: constructs outside the `defineTool` subset degrade to `unknown`, never throw.
- **The dispatch bridge** (`run_code`'s execute): every binding call is JSON-normalized before dispatch (a value that does not survive — `BigInt`, circulars — rejects that one call, so the dispatched form and logged form are the same JSON value by construction), serialized through a per-run queue (even `Promise.all` executes underlying calls one at a time in submission order), given the outer execution's opaque token as `parent`, and run through the complete pre-execute → guards → execute → post-execute → result pipeline. A denial reaches the program as a binding rejection, and each sub-call is logged as a `tool/code-dispatch` session event with deterministic id `<parent>:code:<n>`; `deriveMessages()` does not surface that event. Token correlation lets commit-style observers defer an inner success until the final `run_code` result without exposing the live outer execution; ordinary tool side effects are not rolled back. A sub-call's `additionalContext` is deliberately dropped because inserting it inside a running parent call would break tool-call/result adjacency.
- **Settlement discipline**: the bridge owns a run-scoped abort that follows the outer signal in and fires when the run settles for any reason, so a budget expiry aborts an in-flight sub-tool instead of orphaning it; the bridge then drains its queue BEFORE returning, so every `tool/code-dispatch` lands inside the open turn. A failed run throws `CodeRunFailedError` (`code: 'CODE_RUN_FAILED'`, message = the failure kind + captured logs), which the pipeline converts to a structured `isError` the model self-corrects from.

The wire collapse is the registry's own contribution (`systemPrompt.tools()` is mode-aware), so the logged `request/header` records it for free. With no deliberate schema-adding assembly listener, `code` assembles exactly `[run_code]`, pinned by tests and the snapshot goldens; protection guarantees that `run_code` and `tools:sdk` remain present, not that unrelated listener additions are erased. Try it: `pnpm run demo:code-mode` ([the coding-agent example's Code Mode overlay](../../../examples/coding-agent/README.md#code-mode)); `pnpm run demo:code-mode acp` serves the same mode over ACP instead of the REPL.

### What is NOT here (TODO)

- **Concurrency metadata** — tool definitions do not declare whether executions are safe to overlap.
- **Parallel execution** — the loop and Code Mode bridge execute tool calls sequentially until that metadata exists.
