refactor(downloader): take &self across the downloader hierarchy

Concurrent package operations call into the same downloader instances
through Rc<RefCell<dyn DownloaderInterface>>; with &mut self methods
every call holds a RefMut across its awaits, which panics with
'already mutably borrowed' the moment two operations overlap. This is
groundwork for fanning out InstallationManager's download/install
loops (same rework HttpDownloader/CurlDownloader already got).

- DownloaderInterface/ChangeReportInterface/ArchiveDownloader/
  VcsDownloader methods now take &self; as_change_report_interface
  returns &dyn instead of &mut dyn.
- Implementors move their genuinely mutable state behind cells:
  FileDownloader.additional_cleanup_paths, the archive downloaders'
  cleanup_executed, ZipDownloader.zip_archive_object,
  VcsDownloaderBase.has_cleaned_changes, GitDownloader's stash/discard/
  cache maps and GitUtil, SvnDownloader.cache_credentials,
  PerforceDownloader.perforce. FileDownloader.io gains a RefCell layer
  so get_local_changes can keep PHP's NullIO swap under &self.
- ProcessExecutor::execute_async now returns a future that captures
  everything up front instead of borrowing the executor, and call
  sites build the future before awaiting, so no borrow on the shared
  executor is held while a subprocess runs.
- Filesystem::remove_directory_async becomes remove_directory_async_via
  taking the Rc handle: the Filesystem is only borrowed for the sync
  head/tail, never across the rm subprocess await (sync borrow_mut
  users like rename/ensure_directory_exists would otherwise collide).
- DownloadManager async call sites hold shared borrows only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

1 files changed, 12 insertions, 22 deletions

diff --git a/crates/shirabe/src/downloader/gzip_downloader.rs b/crates/shirabe/src/downloader/gzip_downloader.rs
index 4ea2a327..4ea8f3b9 100644
--- a/crates/shirabe/src/downloader/gzip_downloader.rs
+++ b/crates/shirabe/src/downloader/gzip_downloader.rs
@@ -22,7 +22,7 @@ use shirabe_php_shim::{
 #[derive(Debug)]
 pub struct GzipDownloader {
     inner: FileDownloader,
-    cleanup_executed: IndexMap<String, bool>,
+    cleanup_executed: std::cell::RefCell<IndexMap<String, bool>>,
 }
 
 impl GzipDownloader {
@@ -45,7 +45,7 @@ impl GzipDownloader {
                 Some(filesystem),
                 Some(process),
             ),
-            cleanup_executed: IndexMap::new(),
+            cleanup_executed: std::cell::RefCell::new(IndexMap::new()),
         }
     }
 
@@ -69,20 +69,12 @@ impl ArchiveDownloader for GzipDownloader {
         &self.inner
     }
 
-    fn inner_mut(&mut self) -> &mut FileDownloader {
-        &mut self.inner
-    }
-
-    fn cleanup_executed(&self) -> &IndexMap<String, bool> {
+    fn cleanup_executed(&self) -> &std::cell::RefCell<IndexMap<String, bool>> {
         &self.cleanup_executed
     }
 
-    fn cleanup_executed_mut(&mut self) -> &mut IndexMap<String, bool> {
-        &mut self.cleanup_executed
-    }
-
     async fn extract(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         file: &str,
         path: &str,
@@ -149,7 +141,7 @@ impl ArchiveDownloader for GzipDownloader {
 
 impl ChangeReportInterface for GzipDownloader {
     fn get_local_changes(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
     ) -> anyhow::Result<Option<String>> {
@@ -163,14 +155,12 @@ impl crate::downloader::DownloaderInterface for GzipDownloader {
         self.inner.get_installation_source()
     }
 
-    fn as_change_report_interface(
-        &mut self,
-    ) -> Option<&mut dyn crate::downloader::ChangeReportInterface> {
+    fn as_change_report_interface(&self) -> Option<&dyn crate::downloader::ChangeReportInterface> {
         Some(self)
     }
 
     async fn download(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         prev_package: Option<PackageInterfaceHandle>,
@@ -182,7 +172,7 @@ impl crate::downloader::DownloaderInterface for GzipDownloader {
     }
 
     async fn prepare(
-        &mut self,
+        &self,
         r#type: &str,
         package: PackageInterfaceHandle,
         path: &str,
@@ -192,7 +182,7 @@ impl crate::downloader::DownloaderInterface for GzipDownloader {
     }
 
     async fn install(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         output: bool,
@@ -201,7 +191,7 @@ impl crate::downloader::DownloaderInterface for GzipDownloader {
     }
 
     async fn update(
-        &mut self,
+        &self,
         initial: PackageInterfaceHandle,
         target: PackageInterfaceHandle,
         path: &str,
@@ -210,7 +200,7 @@ impl crate::downloader::DownloaderInterface for GzipDownloader {
     }
 
     async fn remove(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         output: bool,
@@ -219,7 +209,7 @@ impl crate::downloader::DownloaderInterface for GzipDownloader {
     }
 
     async fn cleanup(
-        &mut self,
+        &self,
         r#type: &str,
         package: PackageInterfaceHandle,
         path: &str,