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, 13 insertions, 19 deletions

diff --git a/crates/shirabe/src/downloader/fossil_downloader.rs b/crates/shirabe/src/downloader/fossil_downloader.rs
index 7f610463..9442e87c 100644
--- a/crates/shirabe/src/downloader/fossil_downloader.rs
+++ b/crates/shirabe/src/downloader/fossil_downloader.rs
@@ -76,16 +76,12 @@ impl VcsDownloader for FossilDownloader {
         &self.inner.filesystem
     }
 
-    fn has_cleaned_changes(&self) -> &IndexMap<String, bool> {
+    fn has_cleaned_changes(&self) -> &std::cell::RefCell<IndexMap<String, bool>> {
         &self.inner.has_cleaned_changes
     }
 
-    fn has_cleaned_changes_mut(&mut self) -> &mut IndexMap<String, bool> {
-        &mut self.inner.has_cleaned_changes
-    }
-
     async fn do_download(
-        &mut self,
+        &self,
         _package: PackageInterfaceHandle,
         _path: &str,
         _url: &str,
@@ -95,7 +91,7 @@ impl VcsDownloader for FossilDownloader {
     }
 
     async fn do_install(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         url: &str,
@@ -155,7 +151,7 @@ impl VcsDownloader for FossilDownloader {
     }
 
     async fn do_update(
-        &mut self,
+        &self,
         _initial: PackageInterfaceHandle,
         target: PackageInterfaceHandle,
         path: &str,
@@ -207,7 +203,7 @@ impl VcsDownloader for FossilDownloader {
     }
 
     fn get_commit_logs(
-        &mut self,
+        &self,
         _from_reference: &str,
         to_reference: &str,
         path: &str,
@@ -258,7 +254,7 @@ impl VcsDownloader for FossilDownloader {
 
 impl ChangeReportInterface for FossilDownloader {
     fn get_local_changes(
-        &mut self,
+        &self,
         _package: PackageInterfaceHandle,
         path: &str,
     ) -> anyhow::Result<Option<String>> {
@@ -291,9 +287,7 @@ impl VcsCapableDownloaderInterface for FossilDownloader {
 
 #[async_trait::async_trait(?Send)]
 impl DownloaderInterface for FossilDownloader {
-    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)
     }
 
@@ -308,7 +302,7 @@ impl DownloaderInterface for FossilDownloader {
     }
 
     async fn download(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         prev_package: Option<PackageInterfaceHandle>,
@@ -318,7 +312,7 @@ impl DownloaderInterface for FossilDownloader {
     }
 
     async fn prepare(
-        &mut self,
+        &self,
         r#type: &str,
         package: PackageInterfaceHandle,
         path: &str,
@@ -328,7 +322,7 @@ impl DownloaderInterface for FossilDownloader {
     }
 
     async fn install(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         _output: bool,
@@ -337,7 +331,7 @@ impl DownloaderInterface for FossilDownloader {
     }
 
     async fn update(
-        &mut self,
+        &self,
         initial: PackageInterfaceHandle,
         target: PackageInterfaceHandle,
         path: &str,
@@ -346,7 +340,7 @@ impl DownloaderInterface for FossilDownloader {
     }
 
     async fn remove(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         _output: bool,
@@ -355,7 +349,7 @@ impl DownloaderInterface for FossilDownloader {
     }
 
     async fn cleanup(
-        &mut self,
+        &self,
         r#type: &str,
         package: PackageInterfaceHandle,
         path: &str,