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, 3 insertions, 2 deletions

diff --git a/crates/shirabe/tests/util/auth_helper_test.rs b/crates/shirabe/tests/util/auth_helper_test.rs
index ef5daaf7..6b376f97 100644
--- a/crates/shirabe/tests/util/auth_helper_test.rs
+++ b/crates/shirabe/tests/util/auth_helper_test.rs
@@ -7,6 +7,7 @@ use shirabe::config::ConfigSourceInterface;
 use shirabe::io::IOInterface;
 use shirabe::io::io_interface;
 use shirabe::util::{AuthHelper, Bitbucket, StoreAuth};
+use shirabe_php_shim::Catch as _;
 use shirabe_php_shim::{PhpMixed, base64_encode, json_encode};
 
 // Mirrors AuthHelperTest::setUp: a DEBUG-verbosity IOMock plus a real Config, both
@@ -560,7 +561,7 @@ fn test_store_auth_with_prompt_invalid_answer() {
     let err = auth_helper
         .store_auth(origin, StoreAuth::Prompt)
         .expect_err("expected a RuntimeException");
-    assert!(err.downcast_ref::<RuntimeException>().is_some());
+    assert!(err.is_instanceof::<RuntimeException>());
 
     // Mirrors PHP's `->with('Do you want to store credentials for '.$origin.' in '.
     // $configSourceName.' ? [Yn] ', $this->anything(), null, 'y')` verification on askAndValidate.
@@ -639,7 +640,7 @@ fn test_prompt_auth_if_needed_git_lab_no_auth_change() {
     );
 
     let err = result.expect_err("expected a TransportException");
-    assert!(err.downcast_ref::<TransportException>().is_some());
+    assert!(err.is_instanceof::<TransportException>());
 
     assert_eq!(
         vec![(