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>

5 files changed, 30 insertions, 14 deletions

diff --git a/crates/shirabe/src/installer/binary_presence_interface.rs b/crates/shirabe/src/installer/binary_presence_interface.rs
index 2c4b2cc..8bc3ff9 100644
--- a/crates/shirabe/src/installer/binary_presence_interface.rs
+++ b/crates/shirabe/src/installer/binary_presence_interface.rs
@@ -3,5 +3,5 @@
 use crate::package::PackageInterfaceHandle;
 
 pub trait BinaryPresenceInterface {
-    fn ensure_binaries_presence(&self, package: PackageInterfaceHandle);
+    fn ensure_binaries_presence(&mut self, package: PackageInterfaceHandle);
 }
diff --git a/crates/shirabe/src/installer/installation_manager.rs b/crates/shirabe/src/installer/installation_manager.rs
index 073625b..8275b41 100644
--- a/crates/shirabe/src/installer/installation_manager.rs
+++ b/crates/shirabe/src/installer/installation_manager.rs
@@ -96,10 +96,9 @@ impl InstallationManager {
     /// code is ever executed.
     pub fn disable_plugins(&mut self) {
         for installer in self.installers.iter_mut() {
-            // TODO(phase-b): $installer instanceof PluginInstaller downcast
-            let plugin_installer: Option<&mut PluginInstaller> = None;
-            let _ = plugin_installer;
-            // if let Some(pi) = plugin_installer { pi.disable_plugins(); }
+            if let Some(plugin_installer) = installer.as_plugin_installer_mut() {
+                plugin_installer.disable_plugins();
+            }
         }
     }
 
@@ -161,12 +160,9 @@ impl InstallationManager {
         };
 
         // if the given installer support installing binaries
-        // TODO(phase-b): $installer instanceof BinaryPresenceInterface downcast
-        let bp: Option<&dyn BinaryPresenceInterface> = None;
-        if let Some(bp) = bp {
+        if let Some(bp) = installer.as_binary_presence_interface() {
             bp.ensure_binaries_presence(package);
         }
-        let _ = installer;
     }
 
     /// Executes solver operation.
diff --git a/crates/shirabe/src/installer/installer_interface.rs b/crates/shirabe/src/installer/installer_interface.rs
index 3056429..20fdb2c 100644
--- a/crates/shirabe/src/installer/installer_interface.rs
+++ b/crates/shirabe/src/installer/installer_interface.rs
@@ -1,5 +1,7 @@
 //! ref: composer/src/Composer/Installer/InstallerInterface.php
 
+use crate::installer::BinaryPresenceInterface;
+use crate::installer::PluginInstaller;
 use crate::package::PackageInterfaceHandle;
 use crate::repository::InstalledRepositoryInterface;
 use shirabe_php_shim::PhpMixed;
@@ -55,6 +57,14 @@ pub trait InstallerInterface: std::fmt::Debug {
 
     fn get_install_path(&self, package: PackageInterfaceHandle) -> Option<String>;
 
+    fn as_binary_presence_interface(&mut self) -> Option<&mut dyn BinaryPresenceInterface> {
+        None
+    }
+
+    fn as_plugin_installer_mut(&mut self) -> Option<&mut PluginInstaller> {
+        None
+    }
+
     fn clone_box(&self) -> Box<dyn InstallerInterface> {
         todo!()
     }
diff --git a/crates/shirabe/src/installer/library_installer.rs b/crates/shirabe/src/installer/library_installer.rs
index b4b2d20..58706d6 100644
--- a/crates/shirabe/src/installer/library_installer.rs
+++ b/crates/shirabe/src/installer/library_installer.rs
@@ -418,13 +418,14 @@ impl InstallerInterface for LibraryInstaller {
             base_path
         })
     }
+
+    fn as_binary_presence_interface(&mut self) -> Option<&mut dyn BinaryPresenceInterface> {
+        Some(self)
+    }
 }
 
 impl BinaryPresenceInterface for LibraryInstaller {
-    fn ensure_binaries_presence(&self, _package: PackageInterfaceHandle) {
-        // TODO(phase-b): trait takes &self but LibraryInstaller::ensure_binaries_presence
-        // requires &mut self due to BinaryInstaller::install_binaries(&mut self, ...).
-        // Revisit the trait or use interior mutability.
-        todo!()
+    fn ensure_binaries_presence(&mut self, package: PackageInterfaceHandle) {
+        LibraryInstaller::ensure_binaries_presence(self, package);
     }
 }
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)
+    }
 }