feat: initialize governed postbox module

src/govoplan_postbox/backend/runtime.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+from govoplan_core.core.registry import PlatformRegistry
+
+
+_registry: PlatformRegistry | None = None
+_service: object | None = None
+
+
+def configure_runtime(*, registry: object) -> None:
+    global _registry, _service
+    if not isinstance(registry, PlatformRegistry):
+        raise RuntimeError("Postbox requires a platform registry")
+    if registry is not _registry:
+        _registry = registry
+        _service = None
+
+
+def get_registry() -> PlatformRegistry:
+    if _registry is None:
+        raise RuntimeError("Postbox runtime has not been configured")
+    return _registry
+
+
+def get_service():
+    global _service
+    if _service is None:
+        from govoplan_postbox.backend.service import PostboxService
+
+        _service = PostboxService.from_registry(get_registry())
+    return _service