refactor(path): build paths with Path::join

Concatenating a directory, MAIN_SEPARATOR and a component reimplements
what Path::join already does. Joining directly also drops the separator
from the intermediate values it used to be baked into, such as
ClassLoader's $pathEnd.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

2 files changed, 10 insertions, 7 deletions

diff --git a/crates/shirabe/src/downloader/gzip_downloader.rs b/crates/shirabe/src/downloader/gzip_downloader.rs
index 3ddca2a4..962c5bb8 100644
--- a/crates/shirabe/src/downloader/gzip_downloader.rs
+++ b/crates/shirabe/src/downloader/gzip_downloader.rs
@@ -90,7 +90,11 @@ impl ArchiveDownloader for GzipDownloader {
             .unwrap_or(""),
             PATHINFO_FILENAME,
         );
-        let target_filepath = format!("{}{}{}", path, std::path::MAIN_SEPARATOR, filename);
+        let target_filepath = std::path::Path::new(path)
+            .join(&filename)
+            .into_os_string()
+            .into_string()
+            .unwrap();
 
         if !Platform::is_windows() {
             let command = vec![
diff --git a/crates/shirabe/src/downloader/path_downloader.rs b/crates/shirabe/src/downloader/path_downloader.rs
index 4be835cd..6a496c6a 100644
--- a/crates/shirabe/src/downloader/path_downloader.rs
+++ b/crates/shirabe/src/downloader/path_downloader.rs
@@ -380,12 +380,11 @@ impl DownloaderInterface for PathDownloader {
                         {
                             let absolute_path =
                                 if !self.inner.filesystem.borrow_mut().is_absolute_path(&path) {
-                                    format!(
-                                        "{}{}{}",
-                                        Platform::get_cwd(false)?,
-                                        std::path::MAIN_SEPARATOR,
-                                        path
-                                    )
+                                    std::path::Path::new(&Platform::get_cwd(false)?)
+                                        .join(&path)
+                                        .into_os_string()
+                                        .into_string()
+                                        .unwrap()
                                 } else {
                                     path.clone()
                                 };