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, 7 insertions, 12 deletions

diff --git a/crates/shirabe/src/io/buffer_io.rs b/crates/shirabe/src/io/buffer_io.rs
index bbe1db9f..d1224fdc 100644
--- a/crates/shirabe/src/io/buffer_io.rs
+++ b/crates/shirabe/src/io/buffer_io.rs
@@ -30,10 +30,9 @@ impl BufferIO {
         let stream = match fopen("php://memory", "rw") {
             Ok(stream) => stream,
             Err(_) => {
-                return Err(RuntimeException {
-                    message: "Unable to open memory output stream".to_string(),
-                    code: 0,
-                }
+                return Err(RuntimeException::new(
+                    "Unable to open memory output stream".to_string(),
+                )
                 .into());
             }
         };
@@ -116,10 +115,7 @@ impl BufferIO {
 
         let mut input = self.inner.input.borrow_mut();
         let Some(streamable) = input.as_streamable_mut() else {
-            return Err(RuntimeException {
-                message: "Setting the user inputs requires at least the version 3.2 of the symfony/console component.".to_string(),
-                code: 0,
-            }
+            return Err(RuntimeException::new("Setting the user inputs requires at least the version 3.2 of the symfony/console component.".to_string())
             .into());
         };
 
@@ -133,10 +129,9 @@ impl BufferIO {
         let stream = match fopen("php://memory", "r+") {
             Ok(stream) => stream,
             Err(_) => {
-                return Err(RuntimeException {
-                    message: "Unable to open memory output stream".to_string(),
-                    code: 0,
-                }
+                return Err(RuntimeException::new(
+                    "Unable to open memory output stream".to_string(),
+                )
                 .into());
             }
         };