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, 6 deletions

diff --git a/crates/shirabe-class-map-generator/src/php_file_parser.rs b/crates/shirabe-class-map-generator/src/php_file_parser.rs
index cf30c240..88676407 100644
--- a/crates/shirabe-class-map-generator/src/php_file_parser.rs
+++ b/crates/shirabe-class-map-generator/src/php_file_parser.rs
@@ -1,7 +1,6 @@
 //! ref: composer/vendor/composer/class-map-generator/src/PhpFileParser.php
 
 use crate::php_file_cleaner::PhpFileCleaner;
-use anyhow::anyhow;
 use indexmap::IndexMap;
 use shirabe_external_packages::composer::pcre::{CaptureKey, Preg};
 use shirabe_php_shim::{
@@ -18,10 +17,7 @@ impl PhpFileParser {
         let extra_types = Self::get_extra_types();
 
         if !function_exists("php_strip_whitespace") {
-            return Err(anyhow!(RuntimeException {
-                message: "Classmap generation relies on the php_strip_whitespace function, but it has been disabled by the disable_functions directive.".to_string(),
-                code: 0,
-            }));
+            return Err(RuntimeException::new("Classmap generation relies on the php_strip_whitespace function, but it has been disabled by the disable_functions directive.".to_string()).into());
         }
 
         // Use @ here instead of Silencer to actively suppress 'unhelpful' output
@@ -63,7 +59,7 @@ impl PhpFileParser {
                 );
             }
 
-            return Err(anyhow!(RuntimeException { message, code: 0 }));
+            return Err(RuntimeException::new(message).into());
         }
 
         // return early if there is no chance of matching anything in this file