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

internal/runtime/orchestration/subagent.go

@@ -11,10 +11,10 @@ import (
 )
 
 // SubAgent is a single spawned sub-agent instance. The identity fields (ID, Goal,
-// RoleID, Mode, AttachInfo, ParentSession, Data, Context, WorkingMemory) are set
-// once at Spawn and never mutated. The lifecycle fields (Status, Summary, Result,
-// Err) are written by the sub-agent's background goroutine and read through the
-// synchronized accessors below, so reading them before the sub-agent finishes is
+// RoleID, PersonaID, Mode, AttachInfo, ParentSession, Data, Context, WorkingMemory)
+// are set once at Spawn and never mutated. The lifecycle fields (Status, Summary,
+// Result, Err) are written by the sub-agent's background goroutine and read through
+// the synchronized accessors below, so reading them before the sub-agent finishes is
 // safe. A sub-agent is terminal exactly once its Done reports true; Join returns
 // once every sub-agent is terminal, Wait once the named ids are.
 //
@@ -26,6 +26,11 @@ type SubAgent struct {
 	Goal string
 	// RoleID is the bound role/persona.
 	RoleID string
+	// PersonaID is the target role the sub-agent runs as: its instructions and its
+	// memory scope (design/22 §8-2). Blank means "run as the spawning turn's role",
+	// the pre-existing behavior. The dispatch tool fills it (validated against the
+	// per-role agent pool) and Spawn stamps it onto the run's session env.
+	PersonaID string
 	// Mode is the bound behavior mode.
 	Mode string
 	// AttachInfo is the free-form attachment text supplied at spawn.
@@ -130,6 +135,7 @@ func (s *SubAgent) Snapshot() SubAgentResult {
 		ID:         s.ID,
 		Goal:       s.Goal,
 		RoleID:     s.RoleID,
+		PersonaID:  s.PersonaID,
 		Mode:       s.Mode,
 		AttachInfo: s.AttachInfo,
 		Status:     s.status,