feat(installer): wire InstallerInterface marker-trait downcasts

Add as_binary_presence_interface and as_plugin_installer_mut to
InstallerInterface following the downloader marker-trait downcast
pattern, so InstallationManager can model the PHP instanceof checks in
ensureBinariesPresence and disablePlugins. Make BinaryPresenceInterface
take &mut self, resolving LibraryInstaller's stubbed trait impl.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/crates/shirabe/src/installer/plugin_installer.rs b/crates/shirabe/src/installer/plugin_installer.rs
index 38fcb0d..00b2210 100644
--- a/crates/shirabe/src/installer/plugin_installer.rs
+++ b/crates/shirabe/src/installer/plugin_installer.rs
@@ -2,6 +2,7 @@
 
 use crate::composer::PartialComposerWeakHandle;
 use crate::installer::BinaryInstaller;
+use crate::installer::BinaryPresenceInterface;
 use crate::installer::InstallerInterface;
 use crate::installer::LibraryInstaller;
 use crate::io::IOInterface;
@@ -176,4 +177,12 @@ impl InstallerInterface for PluginInstaller {
     fn get_install_path(&self, package: PackageInterfaceHandle) -> Option<String> {
         self.inner.get_install_path(package)
     }
+
+    fn as_binary_presence_interface(&mut self) -> Option<&mut dyn BinaryPresenceInterface> {
+        Some(&mut self.inner)
+    }
+
+    fn as_plugin_installer_mut(&mut self) -> Option<&mut PluginInstaller> {
+        Some(self)
+    }
 }