feat: add retry middleware with per-attempt governance orchestration

src/polygateway/middleware/base.py

@@ -0,0 +1,25 @@
+"""洋葱组装(D1): 把中间件序列外→内绑定到终端调用上。"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
+    from polygateway.ports import CallNext, Middleware
+
+
+def compose(middlewares: Sequence[Middleware], terminal: CallNext) -> CallNext:
+    """外→内绑定: compose([A, B], t) 的调用序为 A → B → t。"""
+    handler = terminal
+    for mw in reversed(middlewares):
+        handler = _bind(mw, handler)
+    return handler
+
+
+def _bind(mw: Middleware, nxt: CallNext) -> CallNext:
+    async def call(request):
+        return await mw(request, nxt)
+
+    return call