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/spec.go

@@ -40,6 +40,17 @@ type AgentSpec struct {
 	Goal string
 	// RoleID selects the role/persona the sub-agent is bound to.
 	RoleID string
+	// PersonaID is the role the sub-agent actually runs as (design/22 §8-2): it
+	// answers with that role's instructions and reads/writes that role's memory
+	// scope — "她以该角色身份临时替班". Spawn stamps it onto the sub-agent run's
+	// session env, which is the single input the loop resolves the prompt, the
+	// memory namespace, the emotion and the thinking knobs from, so the four can
+	// never disagree. Blank keeps the pre-existing behavior byte for byte: the
+	// sub-agent inherits the spawning turn's env, i.e. the parent session's role.
+	// The id must be one this process can run with its own agent
+	// (*Scheduler).PersonaKnown; Spawn rejects an unknown one with
+	// ErrUnknownPersona instead of silently falling back to the default role.
+	PersonaID string
 	// Mode selects the behavior mode (e.g. "engineer") for the role.
 	Mode string
 	// Context is the initial, isolated conversation context. Spawn deep-copies
@@ -107,6 +118,12 @@ var (
 	// ErrAgentNotFound is returned by Abort when the sub-agent id is unknown.
 	ErrAgentNotFound = errors.New("orchestration: sub-agent not found")
 
+	// ErrUnknownPersona is returned by Spawn when a spec names a role this process
+	// has no per-role agent for (design/22 §8-2). It is a rejection, not a
+	// fallback: running the sub-agent with the default role's prompt while the
+	// caller asked for another role would silently defeat the request.
+	ErrUnknownPersona = errors.New("orchestration: unknown persona")
+
 	// ErrNoScheduler is returned by the spawn tool when it was built without a
 	// scheduler (a wiring mistake, reported instead of panicking).
 	ErrNoScheduler = errors.New("orchestration: no scheduler configured")