Optionally back /tmp and /var/tmp with stable host directories

src/errors.rs

@@ -33,6 +33,7 @@ pub enum SandboxError {
     NoCommand,
     Seccomp(String),
     SeccompUnsupportedArch(String),
+    PersistentTmpDir(PathBuf, String),
 }
 
 impl std::fmt::Display for SandboxError {
@@ -107,6 +108,9 @@ impl std::fmt::Display for SandboxError {
                 f,
                 "seccomp filtering is not supported on this architecture: {arch} (use --no-seccomp to disable)"
             ),
+            Self::PersistentTmpDir(path, reason) => {
+                write!(f, "persistent-tmp directory '{}': {reason}", path.display())
+            }
         }
     }
 }