feat(phase-c): resolve reflection/downcast phase-b TODOs

Resolve category F phase-b TODOs (class-string, instanceof, get_class,
method_exists, __FILE__, Reflection API, downcast).

- VcsRepository: dispatch drivers through a VcsDriverKind enum
  (instantiate/supports/php_class_name) and add constructors to the
  concrete VCS drivers
- repository downcasts via RepositoryInterfaceHandle::downcast_rc and
  as_any (init/show commands, vcs ValidatingArrayLoader)
- BaseCommand::is_self_update_command override replaces an instanceof
- Factory::create narrows PartialComposer to ComposerHandle via as_full
- InstalledVersions gains set_self_dir/set_installed_is_local_dir,
  replacing Reflection-based static property mutation
- ClassLoader::as_array_iter ports the PHP (array) cast
- drop the unnecessary __FILE__ phar branch in self-update

application get_class(command) reclassified TODO(plugin); buffer_io
StreamableInputInterface downcast and the ValidatingArrayLoader trait
redesign left as tracked TODOs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/crates/shirabe/src/repository/handle.rs b/crates/shirabe/src/repository/handle.rs
index 0d02b83..aa79d5e 100644
--- a/crates/shirabe/src/repository/handle.rs
+++ b/crates/shirabe/src/repository/handle.rs
@@ -66,6 +66,24 @@ impl RepositoryInterfaceHandle {
         self.0.borrow().as_any().is::<T>()
     }
 
+    /// Downcasts the shared handle to a concrete repository type, preserving shared ownership.
+    pub fn downcast_rc<T: RepositoryInterface + 'static>(&self) -> Option<Rc<RefCell<T>>> {
+        if self.0.borrow().as_any().is::<T>() {
+            let rc = self.0.clone();
+            let ptr = Rc::into_raw(rc) as *const RefCell<T>;
+            // SAFETY: is::<T>() proved the value is `T`, and handles are always allocated as
+            // `Rc::new(RefCell::new(concrete))`, so the layout matches `RcBox<RefCell<T>>`.
+            Some(unsafe { Rc::from_raw(ptr) })
+        } else {
+            None
+        }
+    }
+
+    pub fn as_platform_repository(&self) -> Option<PlatformRepositoryHandle> {
+        self.downcast_rc::<PlatformRepository>()
+            .map(PlatformRepositoryHandle::from_rc)
+    }
+
     pub fn count(&self) -> i64 {
         self.0.borrow().count()
     }