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, 9 insertions, 18 deletions

diff --git a/crates/shirabe/src/downloader/rar_downloader.rs b/crates/shirabe/src/downloader/rar_downloader.rs
index ee0148c7..f4f601bc 100644
--- a/crates/shirabe/src/downloader/rar_downloader.rs
+++ b/crates/shirabe/src/downloader/rar_downloader.rs
@@ -114,39 +114,30 @@ impl ArchiveDownloader for RarDownloader {
                     process_error.as_deref().unwrap_or(""),
                 )
             };
-            return Err(RuntimeException {
-                message: error,
-                code: 0,
-            }
-            .into());
+            return Err(RuntimeException::new(error).into());
         }
 
         let rar_archive = RarArchive::open(file);
         if rar_archive.is_none() {
-            return Err(UnexpectedValueException {
-                message: format!("Could not open RAR archive: {}", file),
-                code: 0,
-            }
+            return Err(UnexpectedValueException::new(format!(
+                "Could not open RAR archive: {}",
+                file
+            ))
             .into());
         }
         let rar_archive = rar_archive.unwrap();
 
         let entries = rar_archive.get_entries();
         if entries.is_none() {
-            return Err(RuntimeException {
-                message: "Could not retrieve RAR archive entries".to_string(),
-                code: 0,
-            }
+            return Err(RuntimeException::new(
+                "Could not retrieve RAR archive entries".to_string(),
+            )
             .into());
         }
 
         for entry in entries.unwrap() {
             if !entry.extract(path) {
-                return Err(RuntimeException {
-                    message: "Could not extract entry".to_string(),
-                    code: 0,
-                }
-                .into());
+                return Err(RuntimeException::new("Could not extract entry".to_string()).into());
             }
         }