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>

4 files changed, 9 insertions, 12 deletions

diff --git a/crates/shirabe/src/dependency_resolver/policy_interface.rs b/crates/shirabe/src/dependency_resolver/policy_interface.rs
index 0b37dc5..b2d1263 100644
--- a/crates/shirabe/src/dependency_resolver/policy_interface.rs
+++ b/crates/shirabe/src/dependency_resolver/policy_interface.rs
@@ -12,8 +12,4 @@ pub trait PolicyInterface: std::fmt::Debug {
         literals: Vec<i64>,
         required_package: Option<String>,
     ) -> Vec<i64>;
-
-    fn clone_box(&self) -> Box<dyn PolicyInterface> {
-        todo!()
-    }
 }
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(),
diff --git a/crates/shirabe/src/dependency_resolver/rule_set_generator.rs b/crates/shirabe/src/dependency_resolver/rule_set_generator.rs
index 5979f63..6aabd6a 100644
--- a/crates/shirabe/src/dependency_resolver/rule_set_generator.rs
+++ b/crates/shirabe/src/dependency_resolver/rule_set_generator.rs
@@ -23,7 +23,7 @@ use crate::package::PackageInterfaceHandle;
 
 #[derive(Debug)]
 pub struct RuleSetGenerator {
-    pub(crate) policy: Box<dyn PolicyInterface>,
+    pub(crate) policy: Rc<dyn PolicyInterface>,
     pub(crate) pool: std::rc::Rc<std::cell::RefCell<Pool>>,
     pub(crate) rules: RuleSet,
     pub(crate) added_map: IndexMap<i64, PackageInterfaceHandle>,
@@ -32,7 +32,7 @@ pub struct RuleSetGenerator {
 
 impl RuleSetGenerator {
     pub fn new(
-        policy: Box<dyn PolicyInterface>,
+        policy: Rc<dyn PolicyInterface>,
         pool: std::rc::Rc<std::cell::RefCell<Pool>>,
     ) -> Self {
         Self {
diff --git a/crates/shirabe/src/dependency_resolver/solver.rs b/crates/shirabe/src/dependency_resolver/solver.rs
index 4f8d91d..1fbc3ec 100644
--- a/crates/shirabe/src/dependency_resolver/solver.rs
+++ b/crates/shirabe/src/dependency_resolver/solver.rs
@@ -34,7 +34,7 @@ use crate::package::BasePackageHandle;
 
 #[derive(Debug)]
 pub struct Solver {
-    pub(crate) policy: Box<dyn PolicyInterface>,
+    pub(crate) policy: Rc<dyn PolicyInterface>,
     pub(crate) pool: std::rc::Rc<std::cell::RefCell<Pool>>,
 
     pub(crate) rules: RuleSet,
@@ -60,7 +60,7 @@ impl Solver {
     const BRANCH_LEVEL: usize = 1;
 
     pub fn new(
-        policy: Box<dyn PolicyInterface>,
+        policy: Rc<dyn PolicyInterface>,
         pool: std::rc::Rc<std::cell::RefCell<Pool>>,
         io: std::rc::Rc<std::cell::RefCell<dyn IOInterface>>,
     ) -> Self {
@@ -249,8 +249,7 @@ impl Solver {
 
         self.io
             .write_error3("Generating rules", true, crate::io::DEBUG);
-        let mut rule_set_generator =
-            RuleSetGenerator::new(self.policy.clone_box(), self.pool.clone());
+        let mut rule_set_generator = RuleSetGenerator::new(self.policy.clone(), self.pool.clone());
         // TODO(phase-b): get_rules_for takes Option<Box<dyn PlatformRequirementFilterInterface>>;
         // PHP passes the filter directly. Forwarding `None` here keeps the call typecheckable.
         let _ = platform_requirement_filter.as_ref();