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, 8 insertions, 6 deletions

diff --git a/crates/shirabe/src/dependency_resolver/solver.rs b/crates/shirabe/src/dependency_resolver/solver.rs
index dd5bd383..a9453a3e 100644
--- a/crates/shirabe/src/dependency_resolver/solver.rs
+++ b/crates/shirabe/src/dependency_resolver/solver.rs
@@ -381,10 +381,11 @@ impl Solver {
             let (learn_literal, new_level, new_rule, why) = self.analyze(level, rule)?;
 
             if new_level <= 0 || new_level >= level {
-                return Err(anyhow::anyhow!(SolverBugException::new(format!(
+                return Err(SolverBugException::new(format!(
                     "Trying to revert to invalid level {} from level {}.",
                     new_level, level
-                ))));
+                ))
+                .into());
             }
 
             level = new_level;
@@ -505,12 +506,12 @@ impl Solver {
 
                 let inner_literal = loop {
                     if decision_id <= 0 {
-                        return Err(anyhow::anyhow!(SolverBugException::new(format!(
+                        return Err(SolverBugException::new(format!(
                             "Reached invalid decision id {} while looking through {} for a literal present in the analyzed rule {}.",
                             decision_id,
                             rule.borrow(),
                             analyzed_rule.borrow()
-                        ))));
+                        )).into());
                     }
 
                     decision_id -= 1;
@@ -587,10 +588,11 @@ impl Solver {
         let learned_literal = match learned_literal {
             Some(l) => l,
             None => {
-                return Err(anyhow::anyhow!(SolverBugException::new(format!(
+                return Err(SolverBugException::new(format!(
                     "Did not find a learnable literal in analyzed rule {}.",
                     analyzed_rule.borrow()
-                ))));
+                ))
+                .into());
             }
         };