refactor(composer): unify Composer/PartialComposer via Rc handles

Model PHP's `Composer extends PartialComposer` as a PartialOrFullComposer
enum and merge partial_composer.rs into composer.rs. Introduce
ComposerHandle / PartialComposerHandle (plus their Weak variants) so the
graph can be shared, and build it at once with Rc::new_cyclic in the
factory to resolve the back-reference cycles.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2 files changed, 7 insertions, 5 deletions

diff --git a/crates/shirabe/src/util/http_downloader.rs b/crates/shirabe/src/util/http_downloader.rs
index 8c8b8ef..b5a4923 100644
--- a/crates/shirabe/src/util/http_downloader.rs
+++ b/crates/shirabe/src/util/http_downloader.rs
@@ -14,7 +14,8 @@ use shirabe_php_shim::{
 };
 use shirabe_semver::constraint::Constraint;
 
-use crate::composer::Composer;
+use crate::composer;
+use crate::composer::ComposerHandle;
 use crate::config::Config;
 use crate::downloader::TransportException;
 use crate::exception::IrrecoverableDownloadException;
@@ -595,7 +596,7 @@ impl HttpDownloader {
                         .parse_constraints(versions_value.as_string().unwrap_or(""))?;
                     let composer_constraint = Constraint::new(
                         "==",
-                        &version_parser.normalize(&Composer::get_version(), None)?,
+                        &version_parser.normalize(&composer::get_version(), None)?,
                     );
                     if !constraint.matches(&composer_constraint) {
                         continue;
@@ -633,7 +634,7 @@ impl HttpDownloader {
                         )?;
                         let composer_constraint = Constraint::new(
                             "==",
-                            &version_parser.normalize(&Composer::get_version(), None)?,
+                            &version_parser.normalize(&composer::get_version(), None)?,
                         );
                         if !constraint.matches(&composer_constraint) {
                             continue;
diff --git a/crates/shirabe/src/util/stream_context_factory.rs b/crates/shirabe/src/util/stream_context_factory.rs
index bb1948e..48949c8 100644
--- a/crates/shirabe/src/util/stream_context_factory.rs
+++ b/crates/shirabe/src/util/stream_context_factory.rs
@@ -9,7 +9,8 @@ use shirabe_php_shim::{
     php_uname, stream_context_create, stripos, uasort,
 };
 
-use crate::composer::Composer;
+use crate::composer;
+use crate::composer::ComposerHandle;
 use crate::downloader::TransportException;
 use crate::repository::PlatformRepository;
 use crate::util::Filesystem;
@@ -203,7 +204,7 @@ impl StreamContextFactory {
             let platform_php_version = PlatformRepository::get_platform_php_version();
             let user_agent = format!(
                 "User-Agent: Composer/{} ({os}; {release}; {php_version}; {http_version}{platform}{ci})",
-                Composer::get_version(),
+                composer::get_version(),
                 os = if function_exists("php_uname") {
                     php_uname("s")
                 } else {