test(engine): LRC-LIB-LIBFOLDERS normalize sync fixture paths

Rebuild fixture path components with native separators so expected paths
match directory scans on Windows, including files that have been removed.
This is a prerequisite for Windows validation and overlaps the path-helper
fix in upstream PR #660; it can be dropped once that change lands.

Co-Authored-By: GPT-6 Astra <noreply@openai.com>

crates/engine/src/tests_sync.rs

@@ -32,7 +32,9 @@ impl Scratch {
         Scratch(dir)
     }
     fn path(&self, rel: &str) -> String {
-        self.0.join(rel).to_string_lossy().to_string()
+        // Fixtures use `/`; rebuild components so expected paths match the native separators
+        // returned by directory scans, including for files that have already been removed.
+        self.0.join(rel).components().collect::<PathBuf>().to_string_lossy().into_owned()
     }
 }