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feat(events): interception seams — the typed-Decision surface for hooks

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Reshape the agent's interception surface so every seam returns a small, typed
Decision union, and the set covers the hook points a CC/Codex bridge (and a
native plugin) needs. "Native hooks" are not a package — a native hook is just a
cordis plugin on these canonical events; the bridges (a later PR) only translate
an external protocol onto the same surface.

dsh-agent:
- NEW agent/session-start(agent, source) emit (once before turn 1; SessionStartSource
  startup|resume|clear|compact) — a pure notification, seeds context via inject().
- NEW agent/prompt-submit waterfall → PromptDecision (allow, optionally rewriting the
  prompt or attaching additionalContext, or block).
- RESHAPE agent/turn-continuation boolean → ContinuationDecision ({action:'stop'} |
  {action:'continue', reason?}; a continue reason is recorded as next-step steering).
- New HookContext envelope (required source — inject() would mislabel a missing one).

dsh-tools: split the single tools/execute waterfall into tools/pre-execute
(PreToolDecision allow/deny/ask gate) and tools/post-execute (PostToolDecision
accept/block, optionally replacing content or attaching additionalContext). Core
dispatch sits between as plain code; the tool body keeps its inner try/catch so a
thrown tool still reaches post-execute as an isError. ToolExecutionResult gains
additionalContext (ferried to the loop's per-step buffer). Input rewrite is
deliberately NOT offered (a proposed RFC designs it consistently).

dsh-session: new `rejected` TurnEndReason — a turn whose whole prompt batch was
blocked by prompt-submit.

agent-loop firing points: session-start emitted at create (source threaded —
startup for create/fork, resume for resume()); prompt-submit per drained message
with the always-open-turn rule (a fully-blocked batch is a zero-step rejected
turn); the continuation reshape; post-tool additionalContext buffered and appended
after all tool/results (adjacency). ACP codec maps rejected→cancelled.

A worked native-plugin example (interception.spec.ts) proves all four seams compose
end-to-end through the real loop with NO hook/* events (those belong to the bridge
lib). All existing tools/execute + turn-continuation tests migrated. The
tool-subagent abort test now aborts after a microtask so it still exercises the
live onAbort bridge (execute() awaits pre-execute before the body runs).

RFCs: implemented/feature/2026-06-30-interception-seams.md (the reshape) +
proposed/feature/2026-06-30-pre-tool-input-rewrite.md (the deferred rewrite design).
This commit is contained in:
Tianyi Cui
2026-06-30 17:11:18 +08:00
parent 13c6e847a2
commit dc95a7881d
28 changed files with 1255 additions and 146 deletions
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packages/core/tools/src/index.ts
+149 -26
View File
@@ -1,8 +1,9 @@
/**
* Tool registry and execution waterfall. Plugins register tools; the registry
* Tool registry and execution pipeline. Plugins register tools; the registry
* feeds schemas into the system prompt, and `execute()` dispatches each call
* through the `tools/execute` waterfall for sandbox, permission, and hook
* plugins to wrap or veto.
* through `tools/pre-execute` (the allow/deny gate) → core dispatch →
* `tools/post-execute` (inspect/replace the result, attach context) for
* sandbox, permission, and hook plugins to gate or transform a call.
*
* @module @deepseek-ai/dsh-tools
*/
@@ -10,7 +11,7 @@
import { Context, Service } from 'cordis'
import type { CallId, ContentBlock, ToolSchema } from '@deepseek-ai/dsh-llm'
import { HarnessError } from '@deepseek-ai/dsh-llm'
import type { Agent } from '@deepseek-ai/dsh-agent'
import type { Agent, HookContext } from '@deepseek-ai/dsh-agent'
import type {} from '@deepseek-ai/dsh-system-prompt'
export {
@@ -33,14 +34,31 @@ declare module 'cordis' {
interface Events {
/**
* Waterfall around every tool execution — the single seam where sandbox,
* permission, hook, and plan-mode plugins wrap or veto a call. Listeners
* receive `(exec, next)`: call `next()` to proceed (possibly around your
* own logic), or return a {@link ToolExecutionResult} without calling
* `next()` to short-circuit (veto).
* Waterfall BEFORE a tool runs — the gate where sandbox, permission, and
* hook plugins allow or deny a call (Claude Code's `PreToolUse`). Listeners
* receive `(exec, next)`: call `next()` to delegate to the default (allow),
* or return a {@link PreToolDecision} without calling `next()` to
* short-circuit. A `deny` skips dispatch and yields an `isError` result; the
* tool body never runs. Input rewrite is deliberately NOT offered here (see
* {@link PreToolDecision}); `ask` degrades to deny until the permission
* system lands (`FIXME(permissions)`).
* @mode waterfall
*/
'tools/execute'(this: ToolRegistry, exec: ToolExecution, next: () => Promise<ToolExecutionResult>): Promise<ToolExecutionResult>
'tools/pre-execute'(this: ToolRegistry, exec: ToolExecution, next: () => Promise<PreToolDecision>): Promise<PreToolDecision>
/**
* Waterfall AFTER a tool runs — where hook plugins inspect the result and
* accept it (optionally REPLACING the model-facing content, and/or attaching
* `additionalContext` for the next request) or block it with corrective
* `feedback` (Claude Code's `PostToolUse`). Listeners receive
* `(exec, result, next)`: call `next()` to delegate to the default (accept
* unchanged), or return a {@link PostToolDecision} to override. The core tool
* dispatch sits between the two waterfalls as plain code, all inside
* `execute`'s outer try/catch (and the tool body keeps its own inner
* try/catch, so a thrown tool still reaches `post-execute` as an `isError`
* result).
* @mode waterfall
*/
'tools/post-execute'(this: ToolRegistry, exec: ToolExecution, result: ToolExecutionResult, next: () => Promise<PostToolDecision>): Promise<PostToolDecision>
/**
* A tool was registered or unregistered (the available tool set changed).
* @mode emit
@@ -247,8 +265,54 @@ export interface ToolExecutionResult {
* text in `content` is always present; this is extra structure for code.
*/
error?: ToolErrorInfo
/**
* Extra model-facing context a `tools/post-execute` listener attached for the
* NEXT request (Claude Code's PostToolUse `additionalContext`). It is NOT part
* of this call's `content` — `content`/`feedback` shape the tool RESULT, but
* `additionalContext` is a SEPARATE `context/message`. A step can carry
* multiple tool calls, so the loop BUFFERS every call's `additionalContext`
* and appends them only AFTER all `tool/result`s for the step, keeping
* tool-call/result adjacency intact. Carried on the result purely to ferry it
* from `execute()` up to the loop's per-step buffer.
*/
additionalContext?: HookContext
}
/**
* The decision a `tools/pre-execute` listener returns for one pending call.
* Maps onto Claude Code's `PreToolUse` `permissionDecision`.
*
* - `allow` proceeds to dispatch. (Input rewrite — changing `exec.arguments` —
* is deliberately NOT offered: `tool/call` and `assistant/message` are logged
* BEFORE execution and live consumers, e.g. the ACP bridge and `dsh-tool-bash`
* presentation, read the pre-execution arguments, so an execution-only rewrite
* would desync the UI from what RAN. That consistency redesign is its own
* `proposed` RFC; `TODO(pre-tool-input-rewrite)` anchors it at the call site.)
* - `deny` skips dispatch; the loop records an `isError` result carrying `reason`.
* - `ask` is the permission-prompt intent; until the permission system exists it
* degrades to `deny` (`FIXME(permissions)`).
*/
export type PreToolDecision =
| { kind: 'allow' }
| { kind: 'deny'; reason: string }
| { kind: 'ask'; reason?: string }
/**
* The decision a `tools/post-execute` listener returns for one finished call.
* Maps onto Claude Code's `PostToolUse` decision.
*
* - `accept` keeps the call successful; optional `content` REPLACES the
* model-facing result (clean: `tool/result` is logged AFTER `execute()`
* returns, so a replaced result is the single source of truth for both derived
* history and UI). Optional `additionalContext` rides to the next request.
* - `block` turns the call into an `isError` result whose content is the
* corrective `feedback` (the model is told the call was rejected and why),
* optionally also attaching `additionalContext`.
*/
export type PostToolDecision =
| { kind: 'accept'; content?: ContentBlock[]; additionalContext?: HookContext }
| { kind: 'block'; feedback: ContentBlock[]; additionalContext?: HookContext }
/**
* Best-effort human-readable message from an arbitrary thrown value: Error
* instances use `.message`; non-Error objects with a string `message`
@@ -336,31 +400,90 @@ export class ToolRegistry extends Service {
}
/**
* Execute one tool call through the `tools/execute` waterfall. If the tool is
* not registered, the result is an `isError` carrying a `UNKNOWN_TOOL`
* structured error. If the tool or a waterfall listener throws, the error is
* caught and returned as an `isError` result so the loop records a failed tool
* call instead of failing the whole turn; a thrown {@link HarnessError}
* Execute one tool call through the `tools/pre-execute` → dispatch →
* `tools/post-execute` pipeline. The two waterfalls are the gate (allow/deny)
* and the inspect/transform seam; core dispatch sits between them as plain
* code. The whole thing is wrapped in one outer try/catch so a throwing
* listener (in either waterfall) becomes an `isError` result instead of
* failing the turn; the tool body ALSO keeps its own inner try/catch, so a
* thrown tool becomes an `isError` result that `post-execute` listeners can
* still inspect. If the tool is not registered, the result is an `isError`
* carrying a `UNKNOWN_TOOL` structured error. A thrown {@link HarnessError}
* surfaces its `{ name, code }` on the result.
*/
async execute(exec: ToolExecution): Promise<ToolExecutionResult> {
try {
return await this.ctx.waterfall(this, 'tools/execute', exec, async (): Promise<ToolExecutionResult> => {
try {
const tool = this.store.get(exec.name)
// Unknown tool routes through the same catch as a tool-thrown error, so
// both failure classes get structured `{ name, code }` from one path.
if (!tool) throw new ToolNotFoundError(exec.name)
const content = await tool.execute(exec.arguments, exec)
return { callId: exec.callId, content, isError: false }
} catch (error: unknown) {
return toolErrorResult(exec.callId, error)
// --- Gate: tools/pre-execute. A deny (or an ask, which degrades to deny
// until the permission system lands) skips dispatch entirely. ---
const decision = await this.ctx.waterfall(
this, 'tools/pre-execute', exec,
() => Promise.resolve<PreToolDecision>({ kind: 'allow' }),
)
if (decision.kind !== 'allow') {
// deny → isError. ask has no permission UI yet, so degrade to deny
// (FIXME(permissions)): a forthcoming permission system turns `ask` into
// a real prompt; today it is the conservative "not allowed".
const reason = decision.kind === 'deny'
? decision.reason
: decision.reason ?? `tool "${exec.name}" requires approval (not yet supported)`
const denied: ToolExecutionResult = {
callId: exec.callId,
content: [{ type: 'text', text: `Error: ${reason}` }],
isError: true,
}
})
return await this.postExecute(exec, denied)
}
// --- Core dispatch (plain code between the waterfalls). The tool body's
// own try/catch turns a throw into an isError result so post-execute can
// inspect it; an unknown tool routes through the same catch. ---
let result: ToolExecutionResult
try {
const tool = this.store.get(exec.name)
if (!tool) throw new ToolNotFoundError(exec.name)
const content = await tool.execute(exec.arguments, exec)
result = { callId: exec.callId, content, isError: false }
} catch (error: unknown) {
result = toolErrorResult(exec.callId, error)
}
return await this.postExecute(exec, result)
} catch (error: unknown) {
// Outer backstop: a throwing pre/post-execute listener (or the waterfall
// machinery) becomes an isError result, never a turn failure.
return toolErrorResult(exec.callId, error)
}
}
/**
* Run the `tools/post-execute` waterfall over a dispatched `result` and apply
* its {@link PostToolDecision}: `accept` keeps the call successful (replacing
* `content` when given), `block` turns it into an `isError` whose content is
* the corrective `feedback`. Either decision may attach `additionalContext`,
* which is ferried on the returned result for the loop's per-step buffer.
* Runs inside `execute`'s outer try/catch (a throwing listener → isError).
*/
private async postExecute(exec: ToolExecution, result: ToolExecutionResult): Promise<ToolExecutionResult> {
const decision = await this.ctx.waterfall(
this, 'tools/post-execute', exec, result,
() => Promise.resolve<PostToolDecision>({ kind: 'accept' }),
)
const additionalContext = decision.additionalContext
if (decision.kind === 'block') {
return {
callId: result.callId,
content: decision.feedback,
isError: true,
...additionalContext ? { additionalContext } : {},
}
}
// accept: replace content if supplied, preserve the dispatched isError/error.
return {
...result,
...decision.content ? { content: decision.content } : {},
...additionalContext ? { additionalContext } : {},
}
}
}
function toolErrorResult(callId: ToolExecution['callId'], error: unknown): ToolExecutionResult {