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/json/composer_schema_test.rs b/crates/shirabe/tests/json/composer_schema_test.rs
index 9cbea150..f2a5da44 100644
--- a/crates/shirabe/tests/json/composer_schema_test.rs
+++ b/crates/shirabe/tests/json/composer_schema_test.rs
@@ -9,6 +9,7 @@
 //! which property) is identical to upstream.
 
 use shirabe::json::{JsonFile, JsonValidationException};
+use shirabe_php_shim::Catch as _;
 use shirabe_php_shim::json_decode;
 
 const NAME_PATTERN: &str = r#"^[a-z0-9]([_.-]?[a-z0-9]+)*/[a-z0-9](([_.]|-{1,2})?[a-z0-9]+)*$"#;
@@ -22,7 +23,7 @@ fn check(json: &str) -> Vec<String> {
     match JsonFile::validate_json_schema("test", &data, JsonFile::LAX_SCHEMA, None) {
         Ok(_) => Vec::new(),
         Err(e) => e
-            .downcast_ref::<JsonValidationException>()
+            .catch::<JsonValidationException>()
             .unwrap()
             .get_errors()
             .clone(),