Files
deepseek-harness/packages/core/agent/src/dispatch.ts
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TypeScript

/**
* Fused scope-carrier dispatch for agent-subject events, plus the assembly
* context builder. The ONE sanctioned spelling for dispatching `agent/*`
* events: `agentEvents(ctx, agent).waterfall('agent/request', …)` builds the
* scope carrier ({@link scopeTarget} keyed by the agent) AND injects the
* subject as the first event argument in one move, so the correct dispatch is
* also the shortest — a dispatch site cannot pass a carrier keyed to one
* agent while naming another as the subject, which is the invariant the
* dev-mode scoped-dispatch check asserts at runtime.
*
* @module @deepseek-ai/dsh-agent/dispatch
*/
import type { Context, Events } from 'cordis'
import { scopeTarget } from '@deepseek-ai/dsh-scope'
import type { Scoped } from '@deepseek-ai/dsh-scope'
import type { AssembleContext } from '@deepseek-ai/dsh-system-prompt'
import type { Agent } from './types.ts'
/** Extract the parameter tuple from an event handler type (its `this` is not part of the tuple). */
type Params<F> = F extends (...args: infer P) => unknown ? P : never
/** Extract the return type from an event handler type. */
type Return<F> = F extends (...args: never[]) => infer R ? R : never
/**
* The event names whose subject is an agent: handler parameters start with an
* `Agent` AND the handler declares a `Scoped<Agent>` `this` (the scope-carrier
* contract). The `this` check keeps accidental first-parameter-happens-to-be-
* an-Agent events (or zero-arg events, whose parameter tuple would satisfy a
* bare rest-tuple check via callability) out of the fused-dispatch surface.
*/
export type AgentSubjectEvent = {
[K in keyof Events]: Events[K] extends (this: Scoped<Agent>, ...args: infer P) => unknown
? P extends [Agent, ...unknown[]] ? K : never
: never
}[keyof Events]
/** The event arguments AFTER the injected agent subject. */
type Tail<K extends AgentSubjectEvent> = Params<Events[K]> extends [Agent, ...infer R] ? R : never
/**
* The fused dispatcher {@link agentEvents} returns: each method dispatches the
* named agent-subject event with the agent's scope carrier as `thisArg` and
* the agent itself injected as the first event argument.
*/
export interface AgentEventDispatch {
/**
* Fire-and-forget notification in the agent's scope. Every listener is
* invoked; synchronous throws and returned-promise rejections are logged and
* contained per listener, so a notification cannot veto lifecycle progress
* or starve a later observer.
* @param name - the agent-subject event to emit.
* @param rest - the event's arguments after the injected agent.
*/
emit<K extends AgentSubjectEvent>(name: K, ...rest: Tail<K>): void
/**
* Awaited in-order dispatch (Cordis `serial`) in the agent's scope.
* @param name - the agent-subject event to dispatch.
* @param rest - the event's arguments after the injected agent.
* @returns the serial chain's result (the first bail value, if any).
*/
serial<K extends AgentSubjectEvent>(name: K, ...rest: Tail<K>): Promise<Awaited<Return<Events[K]>>>
/**
* Await listeners in order and return the first value other than `undefined`.
* Unlike Cordis `serial`, this does not silently treat `null` or `false` as
* abstentions. Use it for a runtime-validated public boundary whose declared
* abstention is exactly `undefined` (currently `agent/turn-stop`).
* @param name - the agent-subject event to dispatch.
* @param rest - the event's arguments after the injected agent.
* @returns the first non-undefined listener result, or undefined.
*/
strictSerial<K extends AgentSubjectEvent>(name: K, ...rest: Tail<K>): Promise<Awaited<Return<Events[K]>>>
/**
* Around-middleware dispatch (Cordis `waterfall`) in the agent's scope. The
* declared event parameters already end with the `next` callback, so `rest`
* is exactly the event's arguments after the injected agent — the final
* element being the innermost `next` (the default the listener chain wraps).
* @param name - the agent-subject event to dispatch.
* @param rest - the event's arguments after the injected agent.
* @returns the waterfall's composed result.
*/
waterfall<K extends AgentSubjectEvent>(name: K, ...rest: Tail<K>): Return<Events[K]>
}
/**
* Build the fused dispatcher for `agent`'s events (see the module doc). Cheap
* (one carrier + one small object) — dispatch sites create it per run/turn
* rather than caching it on the agent.
* @param ctx - the context to dispatch through (any context of the app).
* @param agent - the subject agent; also the scope-carrier key.
* @returns the fused dispatcher.
*/
export function agentEvents(ctx: Context, agent: Agent): AgentEventDispatch {
const carrier: Scoped<Agent> = scopeTarget(agent, agent)
// The ordinary dispatch methods forward through Cordis' variadic mixins. The
// fused (carrier, name, agent, ...rest) tuple is provably a valid argument
// list for the matching thisArg overload, but TypeScript cannot relate the
// generic Tail<K> spread back to that overload's conditional parameter
// tuple — hence one contained, shape-preserving cast per method.
return {
emit(name, ...rest) {
// Cordis emit invokes callbacks through Array.map: one synchronous throw
// starves later listeners, and returned promises are discarded. Agent
// notifications are non-vetoing, so resolve the same filtered callback
// set ourselves and contain both failure modes independently.
const args: unknown[] = [carrier, name, agent, ...rest]
const callbacks = ctx.events.dispatch('emit', args)
for (const callback of callbacks) {
try {
const returned: unknown = callback(...args)
void Promise.resolve(returned).catch((error: unknown) => {
ctx.logger.warn(`agent event "${name}" listener rejected: ${renderThrown(error)}`)
})
} catch (error: unknown) {
ctx.logger.warn(`agent event "${name}" listener threw: ${renderThrown(error)}`)
}
}
},
async serial(name, ...rest) {
// eslint-disable-next-line @typescript-eslint/unbound-method -- the events mixin accessor returns a pre-bound function
const serial = ctx.serial as (thisArg: Scoped<Agent>, name: string, ...args: unknown[]) => Promise<never>
return await serial(carrier, name, agent, ...rest)
},
strictSerial(name, ...rest) {
return (async (): Promise<unknown> => {
// EventsService.dispatch applies the carrier filter and emits the same
// internal/dispatch instrumentation as ctx.serial, then mutates `args`
// down to the actual listener parameters. Invoke those callbacks in order
// ourselves so every non-undefined value reaches the caller's validator;
// Cordis serial would discard null/false before validation could see them.
const args: unknown[] = [carrier, name, agent, ...rest]
const callbacks = ctx.events.dispatch('serial', args)
for (const callback of callbacks) {
const result: unknown = await callback(...args)
if (result !== undefined) return result
}
return undefined
})() as Promise<Awaited<Return<Events[typeof name]>>>
},
waterfall(name, ...rest) {
// eslint-disable-next-line @typescript-eslint/unbound-method -- the events mixin accessor returns a pre-bound function
const waterfall = ctx.waterfall as (thisArg: Scoped<Agent>, name: string, ...args: unknown[]) => never
return waterfall(carrier, name, agent, ...rest)
},
}
}
/** Render an arbitrary thrown value without allowing coercion to throw again. */
function renderThrown(value: unknown): string {
try {
return value instanceof Error ? `${value.name}: ${value.message}` : String(value)
} catch {
return '<unrenderable thrown value>'
}
}
/**
* The assembly context for one agent's prompt: the typed `agent` DX field and
* the `scope` layer selector, set together (setting `agent` without `scope`
* silently drops the agent's scoped sections/tools from the assembly — the
* dev invariants flag it). THE way the loop (and any custom driver) builds
* its per-step `ctx.systemPrompt.assemble(…)` input.
* @param agent - the agent the assembly is for.
* @returns the context to pass to `assemble()`.
*/
export function assembleContextFor(agent: Agent): AssembleContext {
return { agent, scope: agent }
}