M9 补丁：启动冒烟修复——镜树列表 str 属性访问、内置能力平台作用域与种子提交缺失

真实进程冒烟（灵台+神识起进程 → 登录 → 能力目录 → 授契 → 调用）抓到三处缺陷，全量测试因分支未覆盖而漏网：
① mirror_tree.list_trees：select(Character.id).scalars() 已返回 id 字符串，c.id 属性访问在有 character 的 owner 上必炸（M2a 引入，测试只走了无 character 分支）——改为直接收集
② 内置能力种子写死 owner_scope=local-user，真实用户（UUID owner）查不到能力目录——引入 PLATFORM_SCOPE：builtin 能力挂平台域全局可见可授契，自定义能力仍按 owner 隔离
③ ensure_governance_seed 缺 session.commit——种子数据未提交即随启动 session 回滚（直调误读为成功因同 session 可见未提交数据）
冒烟证据：未授契调用 403 HJ-1303 留痕 → 授行契 → 调用 ok 返回观察标证；能力目录 4 项（builtin.datetime/echo/qiankun.shell/web.fetch）；全量回归 349 passed 不变
另：本地 .env 补入神识段（SHENSHI_BASE_URL=127.0.0.1:8080 接真神识）

backend/app/domains/baigong/service.py

@@ -26,10 +26,20 @@ from app.models.safety import AuditEvent, PendingConfirmationRecord
 from app.schemas.auth import CurrentUser
 
 
+# 内置能力挂平台作用域（全局可见可授契；自定义能力按 owner 隔离）
+PLATFORM_SCOPE = "__platform__"
+
+
+def _capability_visible(cap: Capability, owner_scope: str) -> bool:
+    return cap.owner_scope == owner_scope or (
+        cap.owner_scope == PLATFORM_SCOPE and cap.source == "builtin"
+    )
+
+
 async def _get_capability(capability_id: str, owner_scope: str) -> Capability:
     async with AsyncSessionLocal() as session:
         cap = await session.get(Capability, capability_id)
-        if cap is None or cap.owner_scope != owner_scope:
+        if cap is None or not _capability_visible(cap, owner_scope):
             raise AppError("not_found", "能力不存在。", status_code=404)
         session.expunge(cap)
         return cap
@@ -300,15 +310,24 @@ async def resolve_petition(petition_id: str, approved: bool) -> dict[str, Any]:
 
 async def list_capabilities(owner_scope: str) -> list[dict[str, Any]]:
     async with AsyncSessionLocal() as session:
-        caps = (
-            (
-                await session.execute(
-                    select(Capability).where(Capability.owner_scope == owner_scope)
+        caps = [
+            c
+            for c in (
+                (
+                    await session.execute(
+                        select(Capability).where(
+                            (Capability.owner_scope == owner_scope)
+                            | (
+                                (Capability.owner_scope == PLATFORM_SCOPE)
+                                & (Capability.source == "builtin")
+                            )
+                        )
+                    )
                 )
+                .scalars()
+                .all()
             )
-            .scalars()
-            .all()
-        )
+        ]
         mandates = (
             (
                 await session.execute(

backend/app/domains/mirror_tree/service.py

@@ -120,14 +120,15 @@ async def create_tree(*, character_id: str, owner_scope: str, title: str, defaul
 
 async def list_trees(owner_scope: str, character_id: str | None = None) -> list[MirrorTree]:
     async with AsyncSessionLocal() as session:
-        character_ids = [
-            c.id
-            for c in (
+        character_ids = list(
+            (
                 await session.execute(
                     select(Character.id).where(Character.owner_scope == owner_scope)
                 )
-            ).scalars()
-        ]
+            )
+            .scalars()
+            .all()
+        )
         if not character_ids:
             return []
         stmt = select(MirrorTree).where(