Keep permission regression probe independent of private checkout paths

core/archipelago/src/session_secret.rs

@@ -146,6 +146,7 @@ mod tests {
 
     #[test]
     fn unreadable_existing_key_is_not_replaced() {
+        use std::os::fd::AsRawFd;
         use std::os::unix::process::CommandExt;
         let dir = tempfile::tempdir().unwrap();
         fs::set_permissions(dir.path(), fs::Permissions::from_mode(0o755)).unwrap();
@@ -155,7 +156,11 @@ mod tests {
         if unsafe { libc::geteuid() } == 0 {
             // The isolated runner is root. Probe as an unprivileged child so
             // DAC_OVERRIDE cannot hide the exact production failure.
-            let status = std::process::Command::new(std::env::current_exe().unwrap())
+            // Execute an already-open inode: the test checkout may live under
+            // a private home directory which the probe must not traverse.
+            let executable = File::open(std::env::current_exe().unwrap()).unwrap();
+            let status =
+                std::process::Command::new(format!("/proc/self/fd/{}", executable.as_raw_fd()))
                     .args([
                         "--ignored",
                         "--exact",