feat(installer): register default installers after Composer Rc is built

LibraryInstaller and PluginInstaller upgrade the Composer back-reference
in their constructors, so they could not be built inside Rc::new_cyclic
where the weak handle is not yet upgradeable. Defer create_default_
installers until after the cyclic Rc is established, where the weak
handle resolves, and implement it to register Library -> Plugin ->
Metapackage with a single shared BinaryInstaller.

To share one BinaryInstaller (as Composer does), LibraryInstaller's
binary_installer becomes Rc<RefCell<dyn BinaryInstallerInterface>>
instead of an owned Box; PluginInstaller and the __set_binary_installer
test seam follow.

This clears "Unknown installer type: metapackage". Un-ignores the six
remove tests that now pass; the remaining install/remove tests are
re-labeled for the next blocker (InstallationManager::execute_batch
still leaves the install/cleanup/repo.write promise chain as a todo!()
stub, so package operations do not actually execute).

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

1 files changed, 3 insertions, 2 deletions

diff --git a/crates/shirabe/src/installer/plugin_installer.rs b/crates/shirabe/src/installer/plugin_installer.rs
index cd4de0a..28e4e0d 100644
--- a/crates/shirabe/src/installer/plugin_installer.rs
+++ b/crates/shirabe/src/installer/plugin_installer.rs
@@ -1,7 +1,6 @@
 //! ref: composer/src/Composer/Installer/PluginInstaller.php
 
 use crate::composer::PartialComposerWeakHandle;
-use crate::installer::BinaryInstaller;
 use crate::installer::BinaryPresenceInterface;
 use crate::installer::InstallerInterface;
 use crate::installer::LibraryInstaller;
@@ -25,7 +24,9 @@ impl PluginInstaller {
         io: std::rc::Rc<std::cell::RefCell<dyn IOInterface>>,
         composer: PartialComposerWeakHandle,
         fs: Option<std::rc::Rc<std::cell::RefCell<Filesystem>>>,
-        binary_installer: Option<BinaryInstaller>,
+        binary_installer: Option<
+            std::rc::Rc<std::cell::RefCell<dyn crate::installer::BinaryInstallerInterface>>,
+        >,
     ) -> Self {
         Self {
             inner: LibraryInstaller::new(