feat: add retry middleware with per-attempt governance orchestration

src/polygateway/middleware/breaker.py

@@ -0,0 +1,58 @@
+"""熔断门封装: 后端故障必须报错而非放行(降级方向铁律,与 QuotaGate 同构)。"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from polygateway.errors import GovernanceBackendError
+
+if TYPE_CHECKING:
+    from polygateway.ports import GateDecision, GateUpdate, ProviderGate
+    from polygateway.types import SourceConfig
+
+
+class BreakerGate:
+    """RetryMW 面向熔断后端的唯一入口;包装一切后端异常。"""
+
+    def __init__(self, gate: ProviderGate) -> None:
+        self._gate = gate
+
+    async def try_enter(self, source: SourceConfig, owner: str) -> GateDecision:
+        try:
+            return await self._gate.try_enter(source.name, owner)
+        except GovernanceBackendError:
+            raise
+        except Exception as exc:
+            raise GovernanceBackendError(f"熔断后端故障(try_enter): {exc}") from exc
+
+    async def record_success(self, entry: GateDecision) -> GateUpdate:
+        try:
+            return await self._gate.record_success(entry)
+        except GovernanceBackendError:
+            raise
+        except Exception as exc:
+            raise GovernanceBackendError(f"熔断后端故障(record_success): {exc}") from exc
+
+    async def record_failure(self, entry: GateDecision, reason: str, force_open: bool) -> GateUpdate:
+        try:
+            return await self._gate.record_failure(entry, reason, force_open)
+        except GovernanceBackendError:
+            raise
+        except Exception as exc:
+            raise GovernanceBackendError(f"熔断后端故障(record_failure): {exc}") from exc
+
+    async def release_probe(self, entry: GateDecision) -> GateUpdate:
+        try:
+            return await self._gate.release_probe(entry)
+        except GovernanceBackendError:
+            raise
+        except Exception as exc:
+            raise GovernanceBackendError(f"熔断后端故障(release_probe): {exc}") from exc
+
+    async def retry_after_s(self, sources: tuple[str, ...]) -> float:
+        try:
+            return await self._gate.retry_after_s(sources)
+        except GovernanceBackendError:
+            raise
+        except Exception as exc:
+            raise GovernanceBackendError(f"熔断后端故障(retry_after_s): {exc}") from exc