diff --git a/crates/fbuild-core/src/file_lock.rs b/crates/fbuild-core/src/file_lock.rs
index 60800344..8b243d74 100644
--- a/crates/fbuild-core/src/file_lock.rs
+++ b/crates/fbuild-core/src/file_lock.rs
@@ -20,6 +20,16 @@ pub struct FileLockGuard {
     _file: File,
 }
 
+impl Drop for FileLockGuard {
+    fn drop(&mut self) {
+        // Unlock explicitly instead of relying on close: macOS can transiently
+        // report contention for a re-acquire racing the close-release
+        // (FastLED/fbuild#1340). Explicit LOCK_UN is the deterministic release;
+        // soldr's lifecycle guard unlocks the same way.
+        let _ = self._file.unlock();
+    }
+}
+
 /// Try to acquire an OS-released lock on `path`.
 ///
 /// Returns `Ok(None)` when another process holds a conflicting lock. The lock
@@ -122,6 +132,26 @@ pub async fn acquire(
 mod tests {
     use super::*;
 
+    /// Post-release re-acquires poll through a short deadline instead of
+    /// asserting single-shot availability: macOS can transiently report
+    /// contention just after close-release (FastLED/fbuild#1340). The
+    /// production contract is poll-and-retry, so the property under test is
+    /// eventual availability.
+    fn reacquire_within(path: &Path, mode: FileLockMode) -> FileLockGuard {
+        let deadline = Instant::now() + Duration::from_secs(1);
+        loop {
+            if let Some(guard) = try_acquire(path, mode).unwrap() {
+                return guard;
+            }
+            assert!(
+                Instant::now() < deadline,
+                "lock at {} did not become available within 1s of release",
+                path.display()
+            );
+            std::thread::sleep(Duration::from_millis(10));
+        }
+    }
+
     #[test]
     fn shared_holders_block_exclusive_until_all_release() {
         let temp = tempfile::tempdir().unwrap();
@@ -145,11 +175,7 @@ mod tests {
                 .is_none()
         );
         drop(second);
-        assert!(
-            try_acquire(&path, FileLockMode::Exclusive)
-                .unwrap()
-                .is_some()
-        );
+        let _third = reacquire_within(&path, FileLockMode::Exclusive);
     }
 
     #[test]
@@ -162,7 +188,7 @@ mod tests {
 
         assert!(try_acquire(&path, FileLockMode::Shared).unwrap().is_none());
         drop(exclusive);
-        assert!(try_acquire(&path, FileLockMode::Shared).unwrap().is_some());
+        let _shared = reacquire_within(&path, FileLockMode::Shared);
     }
 
     #[tokio::test]
diff --git a/crates/fbuild-paths/src/daemon_ownership.rs b/crates/fbuild-paths/src/daemon_ownership.rs
index 07e0a586..ea015504 100644
--- a/crates/fbuild-paths/src/daemon_ownership.rs
+++ b/crates/fbuild-paths/src/daemon_ownership.rs
@@ -186,6 +186,28 @@ mod tests {
     use super::*;
     use tempfile::TempDir;
 
+    /// Post-release re-acquires poll through a short deadline instead of
+    /// asserting single-shot availability: the kernel can transiently report
+    /// contention just after close-release on macOS (FastLED/fbuild#1340), and
+    /// the production contract is poll-and-retry, so the property under test is
+    /// eventual availability. Hard I/O errors still fail immediately.
+    fn reacquire_within<T>(
+        io_context: &str,
+        mut acquire: impl FnMut() -> std::io::Result<Option<T>>,
+    ) -> T {
+        let deadline = std::time::Instant::now() + std::time::Duration::from_secs(1);
+        loop {
+            match acquire().unwrap_or_else(|error| panic!("{io_context}: {error}")) {
+                Some(guard) => return guard,
+                None => assert!(
+                    std::time::Instant::now() < deadline,
+                    "{io_context}: lock did not become available within 1s of release"
+                ),
+            }
+            std::thread::sleep(std::time::Duration::from_millis(10));
+        }
+    }
+
     #[test]
     fn root_ownership_is_exclusive_within_process() {
         let temp = TempDir::new().expect("tempdir");
@@ -200,9 +222,9 @@ mod tests {
             "a second exclusive acquire while the first is held must return None"
         );
         drop(first);
-        let third = RootOwnershipGuard::try_acquire_at(&path)
-            .expect("third acquire io")
-            .expect("lock must be available again after the holder drops");
+        let third = reacquire_within("third acquire io", || {
+            RootOwnershipGuard::try_acquire_at(&path)
+        });
         drop(third);
     }
 
@@ -221,9 +243,9 @@ mod tests {
         let second = try_acquire_spawn_lock_result_at(&path).expect("second acquire io");
         assert!(second.is_none(), "second acquire while held must be None");
         drop(first);
-        let third = try_acquire_spawn_lock_result_at(&path)
-            .expect("third acquire io")
-            .expect("lock must be available after release");
+        let third = reacquire_within("third acquire io", || {
+            try_acquire_spawn_lock_result_at(&path)
+        });
         drop(third);
     }
 
@@ -249,9 +271,7 @@ mod tests {
             "second acquire while held must be None"
         );
         drop(first);
-        try_acquire_spawn_lock_result_at(&path)
-            .expect("re-acquire io")
-            .expect("lock must be available after release");
+        reacquire_within("re-acquire io", || try_acquire_spawn_lock_result_at(&path));
     }
 
     /// Soldr pattern (`spawn_lock_serializes_concurrent_threads`): fire a
diff --git a/dylints/ban_std_pathbuf/src/allowlist.txt b/dylints/ban_std_pathbuf/src/allowlist.txt
index 30f04010..e197b1cf 100644
--- a/dylints/ban_std_pathbuf/src/allowlist.txt
+++ b/dylints/ban_std_pathbuf/src/allowlist.txt
@@ -168,6 +168,9 @@ crates/fbuild-library/src/library/arduino_mbed_core.rs
 crates/fbuild-library/src/library/attiny_core.rs
 crates/fbuild-library/src/library/avr_framework.rs
 crates/fbuild-library/src/library/ch32v_core.rs
+# New-file entry per allowlist policy: clearcore_core.rs (#1333) implements the
+# shared Package/core traits typed in PathBuf; migration is repo-wide (FastLED/fbuild#1339).
+crates/fbuild-library/src/library/clearcore_core.rs
 crates/fbuild-library/src/library/cmsis_atmel.rs
 crates/fbuild-library/src/library/cmsis_framework.rs
 crates/fbuild-library/src/library/esp32_framework/fs_utils.rs