diff --git a/crates/spaceshd/src/lifecycle.rs b/crates/spaceshd/src/lifecycle.rs
index 3412c45..5e46db4 100644
--- a/crates/spaceshd/src/lifecycle.rs
+++ b/crates/spaceshd/src/lifecycle.rs
@@ -19,6 +19,11 @@ pub fn socket_path() -> Result<PathBuf> {
 }
 
 pub fn lock_path() -> Result<PathBuf> {
+    if let Ok(p) = std::env::var("SPACESH_LOCK") {
+        if !p.is_empty() {
+            return Ok(PathBuf::from(p));
+        }
+    }
     Ok(spacesh_dir()?.join("daemon.lock"))
 }
 
@@ -64,6 +69,11 @@ mod tests {
 
     #[test]
     fn lock_is_exclusive_within_process() {
+        let _serial = crate::test_support::serial();
+        // Use a private lock path so a real running daemon (which holds the
+        // global ~/.spacesh/daemon.lock) can't make this test flake.
+        let tmp = std::env::temp_dir().join("spacesh-lock-exclusive-test.lock");
+        std::env::set_var("SPACESH_LOCK", &tmp);
         let first = acquire_instance_lock().unwrap();
         assert!(first.is_some(), "first acquire should succeed");
         // A second attempt from the same process on the same fd path:
@@ -72,6 +82,8 @@ mod tests {
         let second = acquire_instance_lock().unwrap();
         assert!(second.is_none(), "second acquire should be blocked");
         drop(first);
+        std::env::remove_var("SPACESH_LOCK");
+        let _ = std::fs::remove_file(&tmp);
     }
 
     #[test]