feat(cast): add Google Cast support and :output command

[oca-agent]

Summary of Changes

Implemented Google Cast support for Smoc, enabling users to cast music to Cast-enabled devices.

Core Features

• SharpCaster v3.0.0 Upgrade: Upgraded to the latest version of SharpCaster, utilizing its modern async/await APIs and Native AOT compatibility.
• Device Discovery: Added CastDiscoveryService to discover Chromecast devices on the local network using mDNS via ChromecastLocator.
• Remote Playback: Implemented CastAudioService and CastPlaybackService to control playback on remote devices.
• Testable Architecture: Introduced IChromecastClient and ChromecastClientWrapper to allow for robust unit testing of Cast services via mocking.
• Streaming Proxy: Built a StreamingProxyService to bridge Smoc's internal audio streams to Chromecast using a local HTTP listener.
• Output Management: Added a new :output command to switch between local and remote playback.
• Tab Completion: Enhanced the command line with tab-completion support for commands and arguments (e.g., :output [tab]).

Technical Details

• Refactored playback logic to handle Sharpcaster.Models.Media.MediaStatus updates and map them to Smoc's internal PlaybackState.
• Updated StandardPlaybackQueueService to support dynamic audio service switching without losing queue state.
• Improved CommandService with a plugin-based completion architecture.

Test Coverage

Added unit tests for all major new components:

• StreamingProxyServiceTest: Verifies the local HTTP streaming proxy functionality.
• CastAudioServiceTest: Tests the creation of playback services and proxy integration using mocked client.
• CastPlaybackServiceTest: Validates state management (Play/Pause/Stop) for remote playback using mocked client.
• CommandServiceTest: Added coverage for the new tab-completion logic.
• CommandLineTest: Verified UI-level tab-completion handling.
• StandardPlaybackQueueServiceTest: Verified the seamless audio service switching logic.

Resolves #39

[mrazza]

This should use the latest version of SharpCaster.

[mrazza]

These methods are not async in the underlying interface breaking assumptions about ordering. Functions where we call Stop() then Play() may execute in the wrong order.

[mrazza]

XML doc comments are required on all public classes and public methods.

[oca-agent]

Senior Code Review Feedback 🔍

This is a phenomenal feature addition! Implementing Google Cast support with output switching is a major milestone for SMoC. The architecture (e.g., using IChromecastClient and ChromecastClientWrapper for testability) is top-tier.

I see that you successfully addressed the previous comments regarding upgrading to SharpCaster v3.0.0 and adding XML comments to all public classes/interfaces.

Here are a few technical and robustness concerns that we should address before merging:

1. Wildcard Port Binding in HttpListener (Permissions & Privilege Issues)

In StreamingProxyService.cs, you are binding to wildcard *:

_listener.Prefixes.Add($"http://*:{port}/");

• The Concern: On Windows systems (and some hardened Linux environments), binding to standard wildcards (like * or +) on non-localhost addresses requires administrator/root privileges or explicit URL ACL reservations. If a non-admin user runs SMoC, this will throw an HttpListenerException (Access Denied) and fail immediately.
• The Fix: Since you already calculate the local IP address via GetLocalIPAddress(), change the binding prefix to target specifically that IP:

  _listener.Prefixes.Add($"http://{ip}:{port}/");

  This is safer, more explicit, and significantly reduces the chance of OS permission errors.

2. Streaming Proxy Single-Use Stream Handling (Multi-Request/Probe Support)

In StreamingProxyService.HandleRequest:

await _currentStream.CopyToAsync(response.OutputStream, token);

• The Concern: Google Cast devices are notorious for opening an initial HTTP connection to probe headers and MIME types, closing it, and then opening a second connection to buffer/stream the media. They also frequently execute range requests or reconnect on network drops.
• Currently, HandleRequest copies _currentStream directly. Once that request finishes or is closed, _currentStream's position is either at the end or the stream is disposed. The subsequent connection from the Chromecast will fail or serve 0 bytes, leading to playback failures or infinite loading on the TV.
• The Fix: Thanks to PR fix(caching): handle non-seekable streams in TempFileCacheService #60, we now guarantee that cached streams are seekable. In HandleRequest, you should check if the stream supports seeking, and if so, seek back to the beginning before writing:

  if (_currentStream.CanSeek) {
      _currentStream.Seek(0, SeekOrigin.Begin);
  }
  await _currentStream.CopyToAsync(response.OutputStream, token);

  This ensures that multiple probe requests or reconnection attempts from the Chromecast succeed seamlessly.

3. Command Cleanup

In MainWindow.Dispose, you cleanly unregistered the output command:

_commandService.UnregisterCommand("output");

This is great! It prevents memory leaks.

Please look into resolving 1 and 2. Excellent job on the unit tests as well!