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, 15 deletions

diff --git a/crates/shirabe/src/self_update/versions.rs b/crates/shirabe/src/self_update/versions.rs
index 14ad10d8..d3611ede 100644
--- a/crates/shirabe/src/self_update/versions.rs
+++ b/crates/shirabe/src/self_update/versions.rs
@@ -73,14 +73,11 @@ impl Versions {
         io: Option<std::rc::Rc<std::cell::RefCell<dyn IOInterface>>>,
     ) -> anyhow::Result<Result<(), InvalidArgumentException>> {
         if !Self::CHANNELS.contains(&channel.as_str()) {
-            return Ok(Err(InvalidArgumentException {
-                message: format!(
-                    "Invalid channel {}, must be one of: {}",
-                    channel,
-                    Self::CHANNELS.join(", ")
-                ),
-                code: 0,
-            }));
+            return Ok(Err(InvalidArgumentException::new(format!(
+                "Invalid channel {}, must be one of: {}",
+                channel,
+                Self::CHANNELS.join(", ")
+            ))));
         }
 
         let channel_file = format!(
@@ -146,13 +143,10 @@ impl Versions {
             }
         }
 
-        Ok(Err(UnexpectedValueException {
-            message: format!(
-                "There is no version of Composer available for your PHP version ({})",
-                PHP_VERSION
-            ),
-            code: 0,
-        }))
+        Ok(Err(UnexpectedValueException::new(format!(
+            "There is no version of Composer available for your PHP version ({})",
+            PHP_VERSION
+        ))))
     }
 
     fn get_versions_data(&mut self) -> anyhow::Result<PhpMixed> {