feat(agent): unify send(target × wakeup), coalesce context/message into user/message

Replace send/steer/inject with one Agent.send primitive over the
(target × wakeup) matrix; followup/steer/inject become fixed-preset
alias methods on the now-abstract Agent class. Coalesce context/message
into user/message (injected context is a non-user source). Replace
agent/queued with agent/inbox/enqueue/dequeue/discard, add cancel
keepInbox, and add a FIFO-conservation invariant.

packages/goal/command-goal/tests/command-goal.spec.ts

@@ -2,7 +2,7 @@ import { describe, expect, it, vi } from 'vitest'
 import { Context } from 'cordis'
 import Loader from '@cordisjs/plugin-loader'
 import AgentRegistry from '@deepseek-ai/dsh-agent'
-import type { Agent, AgentStatus, InjectOptions } from '@deepseek-ai/dsh-agent'
+import type { Agent, AgentStatus, AliasSendOptions } from '@deepseek-ai/dsh-agent'
 import CommandService from '@deepseek-ai/dsh-commands'
 import GoalService from '@deepseek-ai/dsh-goal'
 import type { GoalRef } from '@deepseek-ai/dsh-goal'
@@ -26,11 +26,11 @@ function nextTurn(session: Session): number {
 }
 
 /** Append one idle injection using the public Agent contract's balanced shape. */
-function appendInjection(session: Session, content: ContentBlock[], options?: InjectOptions): void {
-  const source: MessageSource = options?.source ?? { kind: 'user' }
+function appendInjection(session: Session, content: ContentBlock[], options?: AliasSendOptions): void {
+  const source: MessageSource = options?.source ?? { kind: 'plugin', plugin: '' }
   const turn = nextTurn(session)
   session.append('turn/start', { turn, trigger: { kind: 'injection', source } })
-  session.append('context/message', {
+  session.append('user/message', {
     content,
     source,
     ...options?.meta === undefined ? {} : { meta: options.meta },
@@ -49,6 +49,7 @@ function stubAgent(id: string): { agent: Agent; session: Session } {
     ctx: new Context(),
     get status() { return status },
     send() {},
+    followup() {},
     steer() {},
     inject(content, options) { appendInjection(session, content, options) },
     cancel() { status = 'idle' },
@@ -125,7 +126,7 @@ describe('/goal human command', () => {
     expect(created.text).toContain('Rounds: 0/256')
     expect(created.text).toContain('Activation: armed')
     expect(test.ctx.goals.get(test.agent)?.objective).toBe('finish the release')
-    expect(test.session.events.map(event => event.type)).toEqual(['turn/start', 'context/message', 'turn/end'])
+    expect(test.session.events.map(event => event.type)).toEqual(['turn/start', 'user/message', 'turn/end'])
 
     const count = test.session.events.length
     await expect(run(test, ' replacement')).resolves.toEqual({