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>

2 files changed, 12 insertions, 8 deletions

diff --git a/crates/shirabe/src/exception/irrecoverable_download_exception.rs b/crates/shirabe/src/exception/irrecoverable_download_exception.rs
index a8d2dbb4..ed424eff 100644
--- a/crates/shirabe/src/exception/irrecoverable_download_exception.rs
+++ b/crates/shirabe/src/exception/irrecoverable_download_exception.rs
@@ -5,10 +5,14 @@ use shirabe_php_shim::RuntimeException;
 #[derive(Debug)]
 pub struct IrrecoverableDownloadException(pub RuntimeException);
 
-impl std::fmt::Display for IrrecoverableDownloadException {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.0.fmt(f)
+impl IrrecoverableDownloadException {
+    pub fn new(message: String) -> Self {
+        Self(RuntimeException::new(message))
     }
 }
 
-impl std::error::Error for IrrecoverableDownloadException {}
+shirabe_php_shim::impl_php_exception!(
+    IrrecoverableDownloadException,
+    0,
+    r"Composer\Exception\IrrecoverableDownloadException"
+);
diff --git a/crates/shirabe/src/exception/no_ssl_exception.rs b/crates/shirabe/src/exception/no_ssl_exception.rs
index 968ecfd7..b0470e58 100644
--- a/crates/shirabe/src/exception/no_ssl_exception.rs
+++ b/crates/shirabe/src/exception/no_ssl_exception.rs
@@ -6,10 +6,10 @@ use shirabe_php_shim::RuntimeException;
 #[derive(Debug)]
 pub struct NoSslException(pub RuntimeException);
 
-impl std::fmt::Display for NoSslException {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.0.fmt(f)
+impl NoSslException {
+    pub fn new(message: String) -> Self {
+        Self(RuntimeException::new(message))
     }
 }
 
-impl std::error::Error for NoSslException {}
+shirabe_php_shim::impl_php_exception!(NoSslException, 0, r"Composer\Exception\NoSslException");