feat(io): add as_any downcast shims for IOInterface and OutputInterface

Introduce the cross-cutting downcast base for PHP `instanceof` checks on
io/output trait objects: `IOInterface::as_any` (ConsoleIO/NullIO/BufferIO)
and `OutputInterface::as_console_output_interface` (promoting ConsoleOutput
to a proper ConsoleOutputInterface). Wire the resolved downcasts in
ConsoleIO error output, Auditor table format, and the event dispatcher.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

6 files changed, 25 insertions, 22 deletions

diff --git a/crates/shirabe/src/advisory/auditor.rs b/crates/shirabe/src/advisory/auditor.rs
index 18af0f3..af54d06 100644
--- a/crates/shirabe/src/advisory/auditor.rs
+++ b/crates/shirabe/src/advisory/auditor.rs
@@ -434,8 +434,7 @@ impl Auditor {
     ) -> Result<()> {
         match format {
             Self::FORMAT_TABLE => {
-                // TODO(phase-b): `$io instanceof ConsoleIO` downcast from &dyn IOInterface
-                let io_as_console: Option<&ConsoleIO> = None;
+                let io_as_console = io.as_any().downcast_ref::<ConsoleIO>();
                 if io_as_console.is_none() {
                     return Err(InvalidArgumentException {
                         message: format!(
@@ -610,8 +609,7 @@ impl Auditor {
             return Ok(());
         }
 
-        // TODO(phase-b): `$io instanceof ConsoleIO` downcast from &dyn IOInterface
-        let io_as_console: Option<&ConsoleIO> = None;
+        let io_as_console = io.as_any().downcast_ref::<ConsoleIO>();
         if io_as_console.is_none() {
             return Err(InvalidArgumentException {
                 message: format!(
diff --git a/crates/shirabe/src/event_dispatcher/event_dispatcher.rs b/crates/shirabe/src/event_dispatcher/event_dispatcher.rs
index 237fad4..175b689 100644
--- a/crates/shirabe/src/event_dispatcher/event_dispatcher.rs
+++ b/crates/shirabe/src/event_dispatcher/event_dispatcher.rs
@@ -609,11 +609,8 @@ impl EventDispatcher {
                                 .join(" ");
                             // reusing the output from $this->io is mostly needed for tests, but generally speaking
                             // it does not hurt to keep the same stream as the current Application
-                            // TODO(phase-b): IOInterface needs an `as_any` shim before
-                            // `instanceof ConsoleIO` can be expressed; treat io as a
-                            // generic IOInterface for now.
-                            let downcast: Option<&ConsoleIO> = None;
-                            let output: ConsoleOutput = if let Some(_console_io) = downcast {
+                            let is_console_io = self.io.borrow().as_any().is::<ConsoleIO>();
+                            let output: ConsoleOutput = if is_console_io {
                                 // TODO(plugin): \ReflectionProperty to read private `output` from ConsoleIO
                                 // is required by the original PHP — needs user-decided porting strategy.
                                 let _refl_php_version_gate = PHP_VERSION_ID < 80100;
diff --git a/crates/shirabe/src/io/buffer_io.rs b/crates/shirabe/src/io/buffer_io.rs
index ed87b71..291b64b 100644
--- a/crates/shirabe/src/io/buffer_io.rs
+++ b/crates/shirabe/src/io/buffer_io.rs
@@ -245,7 +245,11 @@ impl crate::io::IOInterfaceMutable for BufferIO {
     }
 }
 
-impl crate::io::IOInterface for BufferIO {}
+impl crate::io::IOInterface for BufferIO {
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+}
 
 impl crate::io::BaseIO for BufferIO {
     fn authentications(
diff --git a/crates/shirabe/src/io/console_io.rs b/crates/shirabe/src/io/console_io.rs
index 2b1c334..b69b68b 100644
--- a/crates/shirabe/src/io/console_io.rs
+++ b/crates/shirabe/src/io/console_io.rs
@@ -142,10 +142,7 @@ impl ConsoleIO {
             messages
         };
 
-        if true == stderr && self.output.is_console_output_interface() {
-            // TODO(phase-b): downcast Box<dyn OutputInterface> to ConsoleOutputInterface
-            let console_output: &dyn ConsoleOutputInterface =
-                todo!("downcast self.output to ConsoleOutputInterface");
+        if stderr && let Some(console_output) = self.output.as_console_output_interface() {
             console_output.get_error_output().write(
                 &Self::to_string_list(&messages).join(if newline { "\n" } else { "" }),
                 newline,
@@ -263,11 +260,8 @@ impl ConsoleIO {
     }
 
     fn get_error_output(&self) -> &dyn OutputInterface {
-        if self.output.is_console_output_interface() {
-            // TODO(phase-b): downcast Box<dyn OutputInterface> to ConsoleOutputInterface
-            return todo!(
-                "downcast self.output to ConsoleOutputInterface and call get_error_output()"
-            );
+        if let Some(console_output) = self.output.as_console_output_interface() {
+            return console_output.get_error_output();
         }
 
         &*self.output
@@ -677,7 +671,11 @@ impl IOInterfaceMutable for ConsoleIO {
     }
 }
 
-impl IOInterface for ConsoleIO {}
+impl IOInterface for ConsoleIO {
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+}
 
 impl BaseIO for ConsoleIO {
     fn authentications(
diff --git a/crates/shirabe/src/io/io_interface.rs b/crates/shirabe/src/io/io_interface.rs
index aac1488..e48f9ce 100644
--- a/crates/shirabe/src/io/io_interface.rs
+++ b/crates/shirabe/src/io/io_interface.rs
@@ -149,7 +149,9 @@ pub trait IOInterfaceMutable {
 
 // PHP `IOInterface`. This is the type used for the shared trait object
 // `dyn IOInterface`; its vtable carries both the immutable and mutable methods.
-pub trait IOInterface: IOInterfaceImmutable + IOInterfaceMutable {}
+pub trait IOInterface: IOInterfaceImmutable + IOInterfaceMutable {
+    fn as_any(&self) -> &dyn std::any::Any;
+}
 
 // Shared-ownership handle for a PHP IO instance (reference semantics). It
 // exposes only the immutable surface; mutating methods (`set_authentication`,
diff --git a/crates/shirabe/src/io/null_io.rs b/crates/shirabe/src/io/null_io.rs
index b0e11f1..85a5fa5 100644
--- a/crates/shirabe/src/io/null_io.rs
+++ b/crates/shirabe/src/io/null_io.rs
@@ -138,7 +138,11 @@ impl IOInterfaceMutable for NullIO {
     }
 }
 
-impl IOInterface for NullIO {}
+impl IOInterface for NullIO {
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+}
 
 impl BaseIO for NullIO {
     fn authentications(