M0：灵台 Kernel 骨架（事件溯源/命台席位/瀑布总线/插件注册）与神识客户端边界，新增 POST /runs 占位闭环与测试，Alembic 基线合并为单一起点

backend/app/kernel/seat.py

@@ -0,0 +1,44 @@
+"""命台席位控制：同一人物同一时刻只有一条前台意识流。
+
+M0 为进程内实现（单人物粒度 asyncio 锁 + 等待计数）；多副本部署在标准档
+切换 Redis 租约（lingtai-runtime.md §8），接口保持不变。
+"""
+
+from __future__ import annotations
+
+from collections import defaultdict
+from contextlib import asynccontextmanager
+from collections.abc import AsyncIterator
+import asyncio
+
+
+class SeatManager:
+    """人物粒度的前台席位。后台受托 Run（kind=background_task）不占席位。"""
+
+    def __init__(self) -> None:
+        self._locks: dict[str, asyncio.Lock] = {}
+        self._waiting: dict[str, int] = defaultdict(int)
+
+    def _lock(self, character_id: str) -> asyncio.Lock:
+        if character_id not in self._locks:
+            self._locks[character_id] = asyncio.Lock()
+        return self._locks[character_id]
+
+    @asynccontextmanager
+    async def foreground(self, character_id: str) -> AsyncIterator[None]:
+        """占用前台席位；同人物并发请求在此排队（Kernel 不变量 2）。"""
+        lock = self._lock(character_id)
+        if lock.locked():
+            self._waiting[character_id] += 1
+            try:
+                async with lock:
+                    yield
+            finally:
+                self._waiting[character_id] -= 1
+        else:
+            async with lock:
+                yield
+
+    def queue_depth(self, character_id: str) -> int:
+        """该人物当前排队等待前台席位的请求数（HJ-1101 附带信息）。"""
+        return self._waiting.get(character_id, 0)