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, 2 insertions, 1 deletions

diff --git a/crates/shirabe/tests/util/git_test.rs b/crates/shirabe/tests/util/git_test.rs
index 907ec38a..dbc06137 100644
--- a/crates/shirabe/tests/util/git_test.rs
+++ b/crates/shirabe/tests/util/git_test.rs
@@ -11,6 +11,7 @@ use shirabe::util::filesystem::Filesystem;
 use shirabe::util::git::Git;
 use shirabe::util::http_downloader::HttpDownloaderMockHandler;
 use shirabe::util::process_executor::{MockExpectation, MockHandler, ProcessExecutor};
+use shirabe_php_shim::Catch as _;
 use shirabe_php_shim::{PhpMixed, RuntimeException};
 
 // No-op ConfigSourceInterface, equivalent to PHPUnit's
@@ -195,7 +196,7 @@ fn test_run_command_private_git_hub_repository_not_initial_clone_not_interactive
     );
 
     let err = result.expect_err("expected a RuntimeException");
-    assert!(err.downcast_ref::<RuntimeException>().is_some());
+    assert!(err.is_instanceof::<RuntimeException>());
 }
 
 // privateGithubWithCredentialsProvider helper.