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, 13 deletions

diff --git a/crates/shirabe/src/command/global_command.rs b/crates/shirabe/src/command/global_command.rs
index 79037e55..78b6f3e6 100644
--- a/crates/shirabe/src/command/global_command.rs
+++ b/crates/shirabe/src/command/global_command.rs
@@ -61,11 +61,10 @@ impl GlobalCommand {
         } else if let Some(completion_input) = input_any.downcast_ref::<CompletionInput>() {
             Ok(completion_input.to_string())
         } else {
-            Err(LogicException {
-                message: "Expected an Input instance that is stringable".to_string(),
-                code: 0,
-            }
-            .into())
+            Err(
+                LogicException::new("Expected an Input instance that is stringable".to_string())
+                    .into(),
+            )
         }
     }
 
@@ -85,17 +84,14 @@ impl GlobalCommand {
             let mut fs = Filesystem::new(None);
             fs.ensure_directory_exists(&home)?;
             if !Path::new(&home).is_dir() {
-                return Err(RuntimeException {
-                    message: "Could not create home directory".to_string(),
-                    code: 0,
-                }
-                .into());
+                return Err(
+                    RuntimeException::new("Could not create home directory".to_string()).into(),
+                );
             }
         }
 
-        chdir(&home).map_err(|_e| RuntimeException {
-            message: format!("Could not switch to home directory \"{}\"", home),
-            code: 0,
+        chdir(&home).map_err(|_e| {
+            RuntimeException::new(format!("Could not switch to home directory \"{}\"", home))
         })?;
 
         if !quiet {