feat(symfony-console): implement the shell completion command plumbing

The _complete and completion commands were registered but always panicked:
get_class_of_command / instantiate_completion_output / tail_debug_log were
todo!() and the completion.bash resource was not shipped.

- make Command::complete return anyhow::Result so completion errors
  propagate to CompleteCommand's catch-all (exit code 2) like PHP
- add Command::get_class as the port hook for PHP's get_class() debug log;
  every command supplies its PHP FQCN via the delegation macro
- embed Resources/completion.bash at compile time (single-binary port);
  get_supported_shells becomes a static list
- implement tail_debug_log by moving the shared output handle into the
  'static process callback
- add OutputInterface::as_console_output so unsupported-shell errors go to
  stderr as in PHP
- fix CompletionInput::bind to keep the argument name PHP assigns in the
  foreach head even when the loop breaks on the first unset argument;
  application-level completion always hit this and returned no suggestions

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

2 files changed, 13 insertions, 0 deletions

diff --git a/crates/shirabe-external-packages/src/symfony/console/output/console_output.rs b/crates/shirabe-external-packages/src/symfony/console/output/console_output.rs
index 254ec2ca..306f1e61 100644
--- a/crates/shirabe-external-packages/src/symfony/console/output/console_output.rs
+++ b/crates/shirabe-external-packages/src/symfony/console/output/console_output.rs
@@ -204,4 +204,7 @@ impl OutputInterface for ConsoleOutput {
     fn get_formatter(&self) -> std::rc::Rc<std::cell::RefCell<dyn OutputFormatterInterface>> {
         self.inner.get_formatter()
     }
+    fn as_console_output(&self) -> Option<&dyn ConsoleOutputInterface> {
+        Some(self)
+    }
 }
diff --git a/crates/shirabe-external-packages/src/symfony/console/output/output_interface.rs b/crates/shirabe-external-packages/src/symfony/console/output/output_interface.rs
index 43810f13..28ebd85c 100644
--- a/crates/shirabe-external-packages/src/symfony/console/output/output_interface.rs
+++ b/crates/shirabe-external-packages/src/symfony/console/output/output_interface.rs
@@ -53,4 +53,14 @@ pub trait OutputInterface: std::fmt::Debug + shirabe_php_shim::AsAny {
 
     /// Returns current output formatter instance.
     fn get_formatter(&self) -> std::rc::Rc<std::cell::RefCell<dyn OutputFormatterInterface>>;
+
+    /// Downcast hook standing in for PHP's `$output instanceof ConsoleOutputInterface`
+    /// (cf. `InputInterface::as_streamable`). Only `ConsoleOutput` returns `Some`.
+    fn as_console_output(
+        &self,
+    ) -> Option<
+        &dyn crate::symfony::console::output::console_output_interface::ConsoleOutputInterface,
+    > {
+        None
+    }
 }