feat(php-shim): give ported exceptions PHP's class hierarchy

Ported exceptions were flat structs reached with `downcast_ref`, so
Composer's `catch (\RuntimeException $e)` only matched the exact leaf
type and `get_class($e)` had nothing to report. Each exception now
embeds an instance of the class it extends and travels inside an
`AnyThrowable`; `Catch::catch`/`catch_mut` walk that chain, and
`PhpClass::php_class_name` yields the PHP FQCN.

Dropping the `std::error::Error` impls from the exception types leaves
`AnyThrowable` as the only route into an `anyhow::Error`, so the walk
cannot be bypassed. A `no_exception_downcast` linter catches the
`downcast::<X>()` calls that would now silently answer `None`.

Three sites change behavior as a result: the `TransportException`
exit-code override reaches `MaxFileSizeExceededException`, the
`catch (\LogicException)` in findSimilar() reaches its subclasses, and
rendered exception titles carry the real class name rather than a
guess. `get_class_err()` is no longer a `todo!()`, which re-enables
FilesystemRepositoryTest::testCorruptedRepositoryFile.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 6 insertions, 14 deletions

diff --git a/crates/shirabe/src/installer/project_installer.rs b/crates/shirabe/src/installer/project_installer.rs
index 59d44410..8b878352 100644
--- a/crates/shirabe/src/installer/project_installer.rs
+++ b/crates/shirabe/src/installer/project_installer.rs
@@ -52,10 +52,10 @@ impl InstallerInterface for ProjectInstaller {
         if std::path::Path::new(install_path).exists()
             && !self.filesystem.borrow().is_dir_empty(install_path)
         {
-            return Err(InvalidArgumentException {
-                message: format!("Project directory {} is not empty.", install_path),
-                code: 0,
-            }
+            return Err(InvalidArgumentException::new(format!(
+                "Project directory {} is not empty.",
+                install_path
+            ))
             .into());
         }
         if !std::path::Path::new(install_path).is_dir() {
@@ -109,11 +109,7 @@ impl InstallerInterface for ProjectInstaller {
         _initial: PackageInterfaceHandle,
         _target: PackageInterfaceHandle,
     ) -> anyhow::Result<Option<PhpMixed>> {
-        Err(InvalidArgumentException {
-            message: "not supported".to_string(),
-            code: 0,
-        }
-        .into())
+        Err(InvalidArgumentException::new("not supported".to_string()).into())
     }
 
     async fn uninstall(
@@ -121,11 +117,7 @@ impl InstallerInterface for ProjectInstaller {
         _repo: &InstalledRepositoryInterfaceHandle,
         _package: PackageInterfaceHandle,
     ) -> anyhow::Result<Option<PhpMixed>> {
-        Err(InvalidArgumentException {
-            message: "not supported".to_string(),
-            code: 0,
-        }
-        .into())
+        Err(InvalidArgumentException::new("not supported".to_string()).into())
     }
 
     fn get_install_path(&self, _package: PackageInterfaceHandle) -> Option<String> {