feat: Add guest execution agent and vsock support

- Introduced a standalone guest execution agent to facilitate command execution within the guest VM over Firecracker's vsock.
- Enhanced FirecrackerClient to support vsock configuration, validating guest CID and UDS path.
- Updated configuration to include vsock settings by default.
- Refactored FirecrackerProcessManager to manage runtime sockets more effectively.
- Implemented guest agent installation and provisioning in the image store.
- Added API endpoints for executing commands in the VM and installing the guest agent.
- Improved error handling for guest execution failures and agent availability.

uvm/server.py

@@ -9,7 +9,10 @@ import ssl
 from typing import Any
 
 from .app import Application, build_application
-from .errors import ConfigurationError, ConflictError, NotFoundError, UvmError, ValidationError
+from .errors import (
+    ConfigurationError, ConflictError, GuestAgentUnavailableError, GuestExecutionError,
+    NotFoundError, UvmError, ValidationError,
+)
 
 
 def create_api(application: Application | None = None, *, host: str | None = None) -> Any:
@@ -49,9 +52,12 @@ def create_api(application: Application | None = None, *, host: str | None = Non
 
     @api.exception_handler(UvmError)
     async def handle_uvm_error(_request: Any, error: UvmError) -> Any:
+        detail: dict[str, Any] = {"message": str(error)}
+        if isinstance(error, GuestExecutionError):
+            detail["outcome_unknown"] = error.outcome_unknown
         return JSONResponse(
             status_code=_http_status_for(error),
-            content={"error": {"message": str(error)}},
+            content={"error": detail},
         )
 
     api.include_router(health_router)
@@ -130,6 +136,10 @@ def _validate_server_settings(
 
 
 def _http_status_for(error: UvmError) -> int:
+    if isinstance(error, GuestAgentUnavailableError):
+        return 503
+    if isinstance(error, GuestExecutionError):
+        return 502
     if isinstance(error, NotFoundError):
         return 404
     if isinstance(error, ConflictError):