categorize sandbox creation failure

Author: Skgland

src/cmd/mod.rs

@@ -95,6 +95,10 @@ pub enum CommandError {
     #[error("sandbox image missing from the local system: {0}")]
     SandboxImageMissing(#[source] Box<CommandError>),
 
+    /// Failed to create the sandbox container
+    #[error("sandbox container could not be created: {0}")]
+    SandboxContainerCreate(#[source] Box<CommandError>),
+
     /// Running rustwide inside a Docker container requires the workspace directory to be mounted
     /// from the host system. This error happens if that's not true, for example if the workspace
     /// lives in a directory inside the container.

src/cmd/sandbox.rs

@@ -282,7 +282,8 @@ impl SandboxBuilder {
 
         let out = Command::new(workspace, "docker")
             .args(&args)
-            .run_capture()?;
+            .run_capture()
+            .map_err(|err| CommandError::SandboxContainerCreate(Box::new(err)))?;
         Ok(Container {
             id: out.stdout_lines()[0].clone(),
             workspace,