feat: remove docker container on shutdown

Add automatic cleanup of Docker containers when the application exits.
Uses a singleton runtime pattern and spawns a detached subprocess for
cleanup to ensure fast exit without blocking the UI.

strix/runtime/__init__.py

@@ -12,17 +12,32 @@ class SandboxInitializationError(Exception):
         self.details = details
 
 
+_global_runtime: AbstractRuntime | None = None
+
+
 def get_runtime() -> AbstractRuntime:
+    global _global_runtime  # noqa: PLW0603
+
     runtime_backend = Config.get("strix_runtime_backend")
 
     if runtime_backend == "docker":
         from .docker_runtime import DockerRuntime
 
-        return DockerRuntime()
+        if _global_runtime is None:
+            _global_runtime = DockerRuntime()
+        return _global_runtime
 
     raise ValueError(
         f"Unsupported runtime backend: {runtime_backend}. Only 'docker' is supported for now."
     )
 
 
-__all__ = ["AbstractRuntime", "SandboxInitializationError", "get_runtime"]
+def cleanup_runtime() -> None:
+    global _global_runtime  # noqa: PLW0603
+
+    if _global_runtime is not None:
+        _global_runtime.cleanup()
+        _global_runtime = None
+
+
+__all__ = ["AbstractRuntime", "SandboxInitializationError", "cleanup_runtime", "get_runtime"]