feat(orchestration,runtime): subagent_spawn 支持指定目标角色（以该角色 instructions + 记忆域运行）

design/22 §8-2（主人 2026-10-03 拍板）：跨角色协作 = 把其他角色以子代理形式派出去，
该子代理以目标角色的 instructions 运行、并按目标角色的记忆作用域读写。

- AgentSpec / SubAgent / SubAgentResult 新增 PersonaID；Options.PersonaExists 作角色解析器
- scheduler：派发前校验角色（ErrUnknownPersona），批量 all-or-nothing；
  run ctx 经 withPersonaEnv 只覆盖 SessionEnv.PersonaID —— ActorEnv/MemWritable 原样复制
  （身份识别靠 channel 元数据，persona 决定她怎么答、不决定她能碰什么：项目红线）
- 记忆归属键改为 PersonaID 优先（回落 RoleID）→ 替班者写的是目标角色的记忆域
- spawntool：schema 顶层与 tasks[] 新增可选 persona；省略 = 与旧行为逐字节一致
- 分支根节点新增 props.persona（可观测性）；SinkMemory 移入 memory.go（守 500 行红线）
- 组合根：personaExists(agent 池)；cmd/cyrene/wire.go +5 行

契约：Docs/api-client.md -> v0.47（graph_update 新增可选 props.persona，纯增量）

验证：go build/vet ./... 绿；internal/runtime/orchestration + cmd/cyrene 测试绿；
      go test -race ./internal/runtime/orchestration -run Persona 绿；
      linux/amd64 + darwin/arm64 交叉编译绿
变异验证：① 目标角色换回父/默认角色（3 处断言 FAIL）② 关调度器侧角色校验 ③ 关工具侧预检

cmd/cyrene/subagent_tool_test.go

@@ -6,6 +6,7 @@ import (
 
 	"git.yeij.top/AskaEth/Cyrene_v2/internal/capability/registry"
 	"git.yeij.top/AskaEth/Cyrene_v2/internal/capability/restrict"
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/agent"
 	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/orchestration"
 	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/tool"
 )
@@ -76,3 +77,31 @@ func TestWireSubagentToolNilScheduler(t *testing.T) {
 		t.Fatal("the tool was registered without a scheduler")
 	}
 }
+
+// TestPersonaExistsMirrorsAgentPool locks the composition-root half of design/22 §8-2:
+// the resolver the scheduler validates a dispatched sub-agent's target persona with
+// must answer exactly like the per-role agent pool — a role is dispatchable precisely
+// when the loop has an agent carrying its instructions, and nothing else is. So a
+// persona with no agent is rejected at dispatch time rather than silently answering as
+// the default role.
+func TestPersonaExistsMirrorsAgentPool(t *testing.T) {
+	t.Parallel()
+	pool := map[string]*agent.Agent{"yuki": {}, "xilian": {}}
+	exists := personaExists(pool)
+
+	if !exists("yuki") || !exists("xilian") {
+		t.Fatal("a pooled role was reported as unrunnable")
+	}
+	if exists("nobody") || exists("") {
+		t.Fatal("an unpooled role id was accepted as runnable")
+	}
+	// The resolver is what orchestration gates the dispatch on, so wire it the same
+	// way wire.go does and check the gate agrees.
+	sched := orchestration.New(orchestration.Options{PersonaExists: personaExists(map[string]*agent.Agent{})})
+	if sched.PersonaKnown("yuki") {
+		t.Fatal("an empty pool accepted a persona; want the dispatch rejected")
+	}
+	if !sched.PersonaKnown("") {
+		t.Fatal("a persona-less dispatch was rejected by an empty pool; want it unaffected")
+	}
+}