feat(dependency-resolver): share policy via Rc, drop clone_box

PolicyInterface::clone_box (a todo!() trait-object clone stub) is removed
in favor of Rc<dyn PolicyInterface> shared ownership, matching PHP's
by-reference sharing of the single $policy object across Solver,
RuleSetGenerator and PoolOptimizer. With PoolOptimizer::new now taking an
Rc, Installer::create_pool_optimizer is implemented faithfully
(return new PoolOptimizer($policy)); create_policy returns the shared Rc.

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

1 files changed, 4 insertions, 2 deletions

diff --git a/crates/shirabe/src/dependency_resolver/pool_optimizer.rs b/crates/shirabe/src/dependency_resolver/pool_optimizer.rs
index 7cba910..446ff56 100644
--- a/crates/shirabe/src/dependency_resolver/pool_optimizer.rs
+++ b/crates/shirabe/src/dependency_resolver/pool_optimizer.rs
@@ -1,5 +1,7 @@
 //! ref: composer/src/Composer/DependencyResolver/PoolOptimizer.php
 
+use std::rc::Rc;
+
 use anyhow::Result;
 use indexmap::IndexMap;
 use shirabe_php_shim::{LogicException, PhpMixed, implode, ksort};
@@ -20,7 +22,7 @@ use crate::package::version::VersionParser;
 #[derive(Debug)]
 pub struct PoolOptimizer {
     /// @var PolicyInterface
-    policy: Box<dyn PolicyInterface>,
+    policy: Rc<dyn PolicyInterface>,
 
     /// @var array<int, true>
     irremovable_packages: IndexMap<i64, bool>,
@@ -48,7 +50,7 @@ struct IdenticalDefinitionPointers {
 }
 
 impl PoolOptimizer {
-    pub fn new(policy: Box<dyn PolicyInterface>) -> Self {
+    pub fn new(policy: Rc<dyn PolicyInterface>) -> Self {
         Self {
             policy,
             irremovable_packages: IndexMap::new(),