diff --git a/crates/pu-core/src/agent_def.rs b/crates/pu-core/src/agent_def.rs
index 4a48014..614e751 100644
--- a/crates/pu-core/src/agent_def.rs
+++ b/crates/pu-core/src/agent_def.rs
@@ -144,7 +144,7 @@ mod tests {
     use tempfile::TempDir;
 
     fn isolate_home(tmp: &TempDir) {
-        unsafe { std::env::set_var("HOME", tmp.path()) };
+        paths::set_home_override(Some(tmp.path().to_path_buf()));
     }
 
     #[test]
diff --git a/crates/pu-core/src/paths.rs b/crates/pu-core/src/paths.rs
index fcf7698..3f89cf1 100644
--- a/crates/pu-core/src/paths.rs
+++ b/crates/pu-core/src/paths.rs
@@ -72,7 +72,25 @@ pub fn global_schedules_dir() -> Result<PathBuf, std::io::Error> {
     Ok(global_pu_dir()?.join("schedules"))
 }
 
+#[cfg(test)]
+thread_local! {
+    static HOME_OVERRIDE: std::cell::RefCell<Option<PathBuf>> = const { std::cell::RefCell::new(None) };
+}
+
+/// Override `home_dir()` for the current test thread. Thread-safe alternative
+/// to `unsafe { std::env::set_var("HOME", ...) }`.
+#[cfg(test)]
+pub(crate) fn set_home_override(path: Option<PathBuf>) {
+    HOME_OVERRIDE.with(|o| *o.borrow_mut() = path);
+}
+
 fn home_dir() -> Result<PathBuf, std::io::Error> {
+    #[cfg(test)]
+    {
+        if let Some(p) = HOME_OVERRIDE.with(|o| o.borrow().clone()) {
+            return Ok(p);
+        }
+    }
     std::env::var("HOME")
         .map(PathBuf::from)
         .map_err(|_| std::io::Error::new(std::io::ErrorKind::NotFound, "$HOME not set"))
diff --git a/crates/pu-core/src/schedule_def.rs b/crates/pu-core/src/schedule_def.rs
index b937a0e..4fb49c7 100644
--- a/crates/pu-core/src/schedule_def.rs
+++ b/crates/pu-core/src/schedule_def.rs
@@ -328,6 +328,10 @@ mod tests {
     use super::*;
     use tempfile::TempDir;
 
+    fn isolate_home(tmp: &TempDir) {
+        paths::set_home_override(Some(tmp.path().to_path_buf()));
+    }
+
     fn make_trigger() -> ScheduleTrigger {
         ScheduleTrigger::AgentDef {
             name: "security-review".to_string(),
@@ -504,6 +508,7 @@ created_at: "2025-06-01T00:00:00Z"
     #[test]
     fn given_local_and_global_schedule_defs_should_list_local_first() {
         let tmp = TempDir::new().unwrap();
+        isolate_home(&tmp);
         let root = tmp.path();
         let local_dir = paths::schedules_dir(root);
         std::fs::create_dir_all(&local_dir).unwrap();
@@ -538,6 +543,7 @@ created_at: "2025-06-01T00:00:00Z"
     #[test]
     fn given_no_schedule_defs_should_return_empty_list() {
         let tmp = TempDir::new().unwrap();
+        isolate_home(&tmp);
         let defs = list_schedule_defs(tmp.path());
         assert!(defs.is_empty());
     }
diff --git a/crates/pu-core/src/swarm_def.rs b/crates/pu-core/src/swarm_def.rs
index f766354..5312838 100644
--- a/crates/pu-core/src/swarm_def.rs
+++ b/crates/pu-core/src/swarm_def.rs
@@ -149,7 +149,7 @@ mod tests {
     use tempfile::TempDir;
 
     fn isolate_home(tmp: &TempDir) {
-        unsafe { std::env::set_var("HOME", tmp.path()) };
+        paths::set_home_override(Some(tmp.path().to_path_buf()));
     }
 
     #[test]
diff --git a/crates/pu-core/src/template.rs b/crates/pu-core/src/template.rs
index 582de67..b6f7ce5 100644
--- a/crates/pu-core/src/template.rs
+++ b/crates/pu-core/src/template.rs
@@ -266,7 +266,7 @@ mod tests {
 
     /// Override HOME so global_pu_dir() points to an empty temp dir.
     fn isolate_home(tmp: &TempDir) {
-        unsafe { std::env::set_var("HOME", tmp.path()) };
+        paths::set_home_override(Some(tmp.path().to_path_buf()));
     }
 
     #[test]