fix(agent): route loop dispatches through prebuilt fused dispatcher

Address review feedback on PR #1738:
- ReactLoopAgent builds its AgentEventDispatch once in the constructor and
  routes every emit/serial/waterfall through it, so hot-path dispatches no
  longer allocate a carrier and dispatcher per call; the public carrier
  field is gone (fused dispatcher is private).
- agentEvents accepts an optional prebuilt carrier.
- The fused payload builder spreads the payload before the injected agent
  so a structurally acceptable payload carrying an agent field can never
  override the subject.
- Regenerate doc graphs; re-record core + architecture + affected Agent
  Note translation pairs; add payload-object event contract Agent Note.

packages/core/agent-loop/src/agent.ts

@@ -7,6 +7,7 @@
 import type {
   Agent,
   AgentCancelCause,
+  AgentEventDispatch,
   AgentOptions,
   AgentStatus,
   CancelOptions,
@@ -14,7 +15,7 @@ import type {
   PreStepDecision,
   RequestErrorAction,
 } from '@deepseek-ai/dsh-agent'
-import { Inbox, agentCarrier, assembleContextFor, emitAgentEvent } from '@deepseek-ai/dsh-agent'
+import { Inbox, agentEvents, assembleContextFor } from '@deepseek-ai/dsh-agent'
 import type { GenerateOptions, LlmCallConfig, Message, PreparedLlmCall } from '@deepseek-ai/dsh-llm'
 import {
   BlockAssembler,
@@ -24,7 +25,7 @@ import {
   errorChain,
   markAgentLoopRequest,
 } from '@deepseek-ai/dsh-llm'
-import type { Scope, Scoped } from '@deepseek-ai/dsh-scope'
+import type { Scope } from '@deepseek-ai/dsh-scope'
 import { createScope } from '@deepseek-ai/dsh-scope'
 import type { EpochHeader, RequestContext, Session, SessionId, TurnEndReason, UserMessage } from '@deepseek-ai/dsh-session'
 import { canonicalHeader, headerEquals } from '@deepseek-ai/dsh-session'
@@ -69,8 +70,8 @@ export class ReactLoopAgent implements Agent {
   readonly scope: Scope
   readonly ctx: Context
 
-  /** Fused scope carrier, built once in the constructor for every dispatch. */
-  readonly carrier: Scoped<Agent>
+  /** Fused dispatcher, built once in the constructor so hot-path dispatches never allocate. */
+  private readonly dispatch: AgentEventDispatch
 
   /** Whether this loop instance has appended its initial/resume request anchor. */
   private requestHeaderLogged = false
@@ -82,11 +83,11 @@ export class ReactLoopAgent implements Agent {
     public readonly options: AgentOptions,
     public readonly session: Session,
   ) {
-    this.carrier = agentCarrier(this)
+    this.dispatch = agentEvents(loopCtx, this)
     this.inbox = new Inbox(session, {
-      inserted: (message) => { emitAgentEvent(loopCtx, this, 'agent/inbox/inserted', { message }) },
-      discarded: (message) => { emitAgentEvent(loopCtx, this, 'agent/inbox/discarded', { message }) },
-      claimed: (message, turn) => { emitAgentEvent(loopCtx, this, 'agent/inbox/claimed', { message, turn }) },
+      inserted: (message) => { this.dispatch.emit('agent/inbox/inserted', { message }) },
+      discarded: (message) => { this.dispatch.emit('agent/inbox/discarded', { message }) },
+      claimed: (message, turn) => { this.dispatch.emit('agent/inbox/claimed', { message, turn }) },
     })
     const lastTurn = session.events.findLast(event => event.type === 'turn/start')?.data.turn ?? 0
     this.phase = { kind: 'idle', lastTurn }
@@ -105,7 +106,7 @@ export class ReactLoopAgent implements Agent {
     this.phase = next
     const status = this.status
     if (status !== previousStatus) {
-      emitAgentEvent(this.loopCtx, this, 'agent/status', { status })
+      this.dispatch.emit('agent/status', { status })
     }
   }
 
@@ -183,7 +184,7 @@ export class ReactLoopAgent implements Agent {
   private throwError(error: unknown): never {
     const turn = this.phase.kind === 'running' ? this.phase.turn : this.phase.lastTurn
     const step = this.phase.kind === 'running' ? this.phase.step : 0
-    emitAgentEvent(this.loopCtx, this, 'agent/error', { turn, step, error })
+    this.dispatch.emit('agent/error', { turn, step, error })
     throw error
   }
 
@@ -209,8 +210,8 @@ export class ReactLoopAgent implements Agent {
     signal.throwIfAborted()
     const sections = renderContextSections(assembly)
     const context = this.runtimeContext.project(joinContextSections(sections), sections)
-    const decision = await this.loopCtx.waterfall(
-      this.carrier, 'agent/pre-step', { agent: this, messages: claimed, ...position, signal },
+    const decision = await this.dispatch.waterfall(
+      'agent/pre-step', { messages: claimed, ...position, signal },
       (): Promise<PreStepDecision> => Promise.resolve<PreStepDecision>({
         kind: 'enter',
         messages: context === undefined ? claimed : [...claimed, context],
@@ -271,7 +272,7 @@ export class ReactLoopAgent implements Agent {
         }
         signal.throwIfAborted()
         if (turnEnds && this.inbox.nextStep.length === 0) {
-          await this.loopCtx.serial(this.carrier, 'agent/turn-stopping', { agent: this, turn, signal })
+          await this.dispatch.serial('agent/turn-stopping', { turn, signal })
           signal.throwIfAborted()
         }
         if (turnEnds && this.inbox.nextStep.length === 0) break
@@ -328,9 +329,8 @@ export class ReactLoopAgent implements Agent {
       signal.throwIfAborted()
       const finish = assembler.finish
       if (finish.kind === 'error' || finish.kind === 'aborted') {
-        const action = await this.loopCtx.waterfall(
-          this.carrier, 'agent/request-error', {
-            agent: this,
+        const action = await this.dispatch.waterfall(
+          'agent/request-error', {
             turn,
             step,
             provider: request.provider,
@@ -412,8 +412,8 @@ export class ReactLoopAgent implements Agent {
           ...maxTokens === undefined ? {} : { maxTokens },
         },
     ))
-    const proposedConfig = await this.loopCtx.waterfall(
-      this.carrier, 'agent/request', { agent: this, turn, step, signal },
+    const proposedConfig = await this.dispatch.waterfall(
+      'agent/request', { turn, step, signal },
       () => Promise.resolve(seedConfig),
     )
     signal.throwIfAborted()