2 files changed, 80 insertions, 5 deletions
diff --git a/crates/shirabe-php-rpc/php/runtime/Shirabe/MaterializedThrowable.php b/crates/shirabe-php-rpc/php/runtime/Shirabe/MaterializedThrowable.php
new file mode 100644
index 00000000..7227a5f3
--- /dev/null
+++ b/crates/shirabe-php-rpc/php/runtime/Shirabe/MaterializedThrowable.php
@@ -0,0 +1,70 @@
+<?php
+
+// The PHP half of the Throw frame's exception codec. A Rust-side failure carries the class it
+// was thrown as, so `catch (TransportException $e)` in plugin code catches what it would catch
+// under Composer, plus the state that class declares beyond message and code.
+
+namespace Shirabe;
+
+final class MaterializedThrowable
+{
+    /**
+     * Rebuilds the exception a Throw frame describes. A class the child cannot construct from a
+     * message and a code keeps the RuntimeException shape, which is all the frame guarantees.
+     *
+     * @param array<string, mixed> $properties
+     */
+    public static function revive(string $class, string $message, int $code, array $properties): \Throwable
+    {
+        $exception = self::instantiate($class, $message, $code);
+        foreach ($properties as $name => $value) {
+            // A name the class does not declare is a Shirabe bug rather than a plugin one, and
+            // ReflectionProperty reports it as such instead of dropping the state silently.
+            $property = new \ReflectionProperty($exception, $name);
+            $property->setAccessible(true);
+            $property->setValue($exception, $value);
+        }
+
+        return $exception;
+    }
+
+    private static function instantiate(string $class, string $message, int $code): \Throwable
+    {
+        if ($class === '' || !class_exists($class) || !is_a($class, \Throwable::class, true)) {
+            return new \RuntimeException($message, $code);
+        }
+        $constructor = (new \ReflectionClass($class))->getConstructor();
+        if ($constructor === null || !self::acceptsMessageAndCode($constructor)) {
+            return new \RuntimeException($message, $code);
+        }
+
+        return new $class($message, $code);
+    }
+
+    /**
+     * Whether the constructor has \Exception's shape as far as the frame fills it in: a string
+     * message, an int code, and nothing else required.
+     */
+    private static function acceptsMessageAndCode(\ReflectionMethod $constructor): bool
+    {
+        $parameters = $constructor->getParameters();
+        if (count($parameters) < 2) {
+            return false;
+        }
+        foreach ($parameters as $position => $parameter) {
+            $type = $parameter->getType();
+            $name = $type instanceof \ReflectionNamedType ? $type->getName() : null;
+            if ($position === 0 && $name !== 'string') {
+                return false;
+            }
+            if ($position === 1 && $name !== 'int') {
+                return false;
+            }
+            if ($position >= 2 && !$parameter->isOptional()) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}
diff --git a/crates/shirabe-php-rpc/php/worker.php b/crates/shirabe-php-rpc/php/worker.php
index bc10c2de..defa4fb5 100644
--- a/crates/shirabe-php-rpc/php/worker.php
+++ b/crates/shirabe-php-rpc/php/worker.php
@@ -337,10 +337,13 @@ final class ShirabeRpcRuntime
                     $outParams = self::fromWire($fields[1] ?? []);
                     return self::fromWire($fields[0]);
                 }
-                [$class, $message, $code] = $fields;
-                // TODO(plugin): reconstruct the original exception class instead of collapsing
-                // everything to RuntimeException.
-                throw new RuntimeException($message, (int) $code);
+                [$class, $message, $code, $properties] = $fields;
+                throw \Shirabe\MaterializedThrowable::revive(
+                    $class,
+                    $message,
+                    (int) $code,
+                    self::fromWire($properties)
+                );
             }
             self::dispatchRequest($tag, $inId, $payload);
         }
@@ -435,7 +438,9 @@ final class ShirabeRpcRuntime
             self::writeFrame(
                 SHIRABE_TAG_THROW,
                 $corrId,
-                serialize([get_class($e), $e->getMessage(), (int) $e->getCode()])
+                // TODO(plugin): the properties field is empty in this direction; no Rust-side
+                // consumer rebuilds a ported exception from a Throw frame yet.
+                serialize([get_class($e), $e->getMessage(), (int) $e->getCode(), []])
             );
         }
     }