feat(plugin): carry an exception's class and state across the boundary

A Rust-side failure reached plugin code as a RuntimeException whose message
carried the name of the call that failed, so `catch (TransportException $e)`
never matched and the status code the plugin branches on was gone.

The Throw frame now names the class the exception was thrown as and carries
the state that class declares beyond message and code.
\Shirabe\MaterializedThrowable rebuilds it in the child: `new $class($message,
$code)` for a class whose constructor has \Exception's shape, then the
properties by reflection. A class the child cannot build that way keeps the
RuntimeException shape.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

2 files changed, 85 insertions, 0 deletions

diff --git a/crates/shirabe-php-rpc/src/frame.rs b/crates/shirabe-php-rpc/src/frame.rs
index 3a355c86..fe7752bd 100644
--- a/crates/shirabe-php-rpc/src/frame.rs
+++ b/crates/shirabe-php-rpc/src/frame.rs
@@ -66,6 +66,9 @@ pub enum Frame {
         exception_class: String,
         message: String,
         code: i64,
+        /// The state the exception carries beyond `message` and `code`, keyed by the property
+        /// names its class declares. Empty for an exception that carries none.
+        properties: IndexMap<String, PluginValue>,
     },
     ReleaseRustHandle {
         rhandle: u64,
@@ -180,11 +183,18 @@ impl Frame {
                 exception_class,
                 message,
                 code,
+                properties,
                 ..
             } => vec![
                 PluginValue::string(exception_class.clone()),
                 PluginValue::string(message.clone()),
                 PluginValue::Int(*code),
+                PluginValue::Array(
+                    properties
+                        .iter()
+                        .map(|(name, v)| (name.clone().into_bytes(), v.clone()))
+                        .collect(),
+                ),
             ],
             Frame::ReleaseRustHandle { rhandle } => vec![int_value(*rhandle)],
             Frame::ReleasePhpHandle { phandle } => vec![int_value(*phandle)],
@@ -302,6 +312,7 @@ fn decode_frame(tag: u8, corr_id: u64, payload: &[u8]) -> Frame {
                     panic!("PHP RPC: protocol violation — Throw code is not an int: {other:?}")
                 }
             },
+            properties: expect_properties(next()),
         },
         TAG_RELEASE_RUST_HANDLE => Frame::ReleaseRustHandle {
             rhandle: expect_id(next()),
@@ -354,6 +365,27 @@ fn expect_positions(value: PluginValue) -> Vec<u32> {
         .collect()
 }
 
+fn expect_properties(value: PluginValue) -> IndexMap<String, PluginValue> {
+    match value {
+        PluginValue::List(items) if items.is_empty() => IndexMap::new(),
+        PluginValue::Array(map) => map
+            .into_iter()
+            .map(|(key, item)| {
+                let name = String::from_utf8(key).unwrap_or_else(|error| {
+                    panic!(
+                        "PHP RPC: protocol violation — exception property name is not UTF-8: {:?}",
+                        String::from_utf8_lossy(error.as_bytes())
+                    )
+                });
+                (name, item)
+            })
+            .collect(),
+        other => {
+            panic!("PHP RPC: protocol violation — exception properties is not an array: {other:?}")
+        }
+    }
+}
+
 fn expect_out_params(value: PluginValue) -> IndexMap<u32, PluginValue> {
     match value {
         PluginValue::List(items) if items.is_empty() => IndexMap::new(),
@@ -416,6 +448,42 @@ mod tests {
     }
 
     #[test]
+    fn frame_roundtrip_throw_with_properties() {
+        let frame = roundtrip(Frame::Throw {
+            corr_id: 11,
+            exception_class: "Composer\\Downloader\\TransportException".to_string(),
+            message: "The \"https://example.org\" file could not be downloaded".to_string(),
+            code: 401,
+            properties: [
+                ("statusCode".to_string(), PluginValue::Int(401)),
+                ("response".to_string(), PluginValue::Null),
+            ]
+            .into_iter()
+            .collect(),
+        });
+        match frame {
+            Frame::Throw {
+                corr_id,
+                exception_class,
+                message,
+                code,
+                properties,
+            } => {
+                assert_eq!(corr_id, 11);
+                assert_eq!(exception_class, "Composer\\Downloader\\TransportException");
+                assert_eq!(
+                    message,
+                    "The \"https://example.org\" file could not be downloaded"
+                );
+                assert_eq!(code, 401);
+                assert_eq!(properties.get("statusCode"), Some(&PluginValue::Int(401)));
+                assert_eq!(properties.get("response"), Some(&PluginValue::Null));
+            }
+            other => panic!("unexpected frame: {other:?}"),
+        }
+    }
+
+    #[test]
     fn frame_roundtrip_return_with_out_params() {
         let frame = roundtrip(Frame::Return {
             corr_id: 9,
diff --git a/crates/shirabe-php-rpc/src/lib.rs b/crates/shirabe-php-rpc/src/lib.rs
index dfd8fa67..c898fb82 100644
--- a/crates/shirabe-php-rpc/src/lib.rs
+++ b/crates/shirabe-php-rpc/src/lib.rs
@@ -621,6 +621,15 @@ pub struct PhpThrow {
     pub exception_class: String,
     pub message: String,
     pub code: i64,
+    /// The state the exception carries beyond `message` and `code`, keyed by the property names
+    /// its class declares. The child revives them onto the instance it rebuilds.
+    ///
+    /// TODO(plugin): populated only Rust to PHP. An exception a plugin throws crosses with its
+    /// class, message and code alone, because no Rust-side consumer rebuilds a ported exception
+    /// from a `PhpThrow` yet.
+    ///
+    /// Boxed so a `Result<_, PhpThrow>` stays small; every dispatcher returns one.
+    pub properties: Box<IndexMap<String, PluginValue>>,
 }
 
 impl PhpThrow {
@@ -629,6 +638,7 @@ impl PhpThrow {
             exception_class: "RuntimeException".to_string(),
             message,
             code: 0,
+            properties: Box::new(IndexMap::new()),
         }
     }
 }
@@ -805,11 +815,13 @@ fn rpc_call(
                 exception_class,
                 message,
                 code,
+                properties,
             } if corr_id == my_id => {
                 return Ok(Err(PhpThrow {
                     exception_class,
                     message,
                     code,
+                    properties: Box::new(properties),
                 }));
             }
             Frame::CallRustMethod {
@@ -846,6 +858,7 @@ fn rpc_call(
                         exception_class: throw.exception_class,
                         message: throw.message,
                         code: throw.code,
+                        properties: *throw.properties,
                     },
                 };
                 send_frame(&reply)?;
@@ -1042,6 +1055,10 @@ const RUNTIME_FILES: &[(&str, &str)] = &[
         include_str!("../php/runtime/Composer/EventDispatcher/Event.php"),
     ),
     (
+        "Shirabe/MaterializedThrowable.php",
+        include_str!("../php/runtime/Shirabe/MaterializedThrowable.php"),
+    ),
+    (
         "Shirabe/MaterializedValue.php",
         include_str!("../php/runtime/Shirabe/MaterializedValue.php"),
     ),