[codex] Fix playback dependency handling and bump version

[thepushkarp]

Summary

• fail fast when playback is requested without mpv
• stop the TUI from claiming playback started when mpv startup fails
• document Brew vs cargo install runtime dependency expectations
• bump the crate version from 0.0.2 to 0.0.3

Why

A fresh install could reach playback code without a working player backend. In the CLI, mls play discovered that late during process spawn. In the TUI, playback start errors were swallowed and the UI could report Playing: ... even though nothing started.

This change makes missing mpv explicit and actionable for the runtime paths that need it while keeping browse/list features usable without playback.

What changed

• return dependency exit code 4 with Playback requires mpv. Install: brew install mpv for mls play when mpv is absent
• normalize playback startup errors into a user-facing message
• only update TUI playback state after a successful start, including triage mode
• add a CLI regression test for missing mpv and a TUI unit test for failed playback startup state
• update install docs so Homebrew and cargo install paths describe different runtime provisioning

Validation

• cargo test
• cargo clippy --all-targets --all-features -- -D warnings
• cargo fmt --check
• PATH="$(pwd)/tests/fixtures/mock_bin" target/debug/mls --quiet play README.md -> exit 4 with install hint

Companion change

A companion PR in thepushkarp/homebrew-tap adds mpv to the Brew formula and verifies the dependency stays declared. These two PRs should merge together.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the robustness and user experience of the media-ls application by addressing issues related to missing playback dependencies. It ensures that users are immediately informed if the mpv player is not available when attempting to play media, both in the command-line interface and the terminal user interface. The changes also streamline error reporting for playback failures and provide clearer installation instructions for runtime dependencies across different installation methods.

Highlights

• Dependency Handling: Implemented fail-fast behavior for the play command when the mpv player is not installed, returning an explicit error code and message.
• TUI Playback Error Handling: Prevented the TUI from incorrectly indicating playback has started when mpv fails to launch, and now displays user-friendly error messages for playback failures.
• Documentation Updates: Clarified runtime dependency expectations in README.md for Homebrew versus cargo install and source builds, detailing the need for ffmpeg, mpv, and trash.
• Version Bump: Bumped the crate version from 0.0.2 to 0.0.3.

Changelog

• Cargo.lock
  • Updated media-ls package version to 0.0.3.
• Cargo.toml
  • Updated media-ls crate version to 0.0.3.
• README.md
  • Updated installation instructions for Homebrew, Cargo, and source builds to clarify runtime dependencies for ffmpeg, mpv, and trash.
• src/deps.rs
  • Added constants for mpv dependency error and warning messages.
• src/main.rs
  • Implemented early exit with an error code if mpv is missing for the play command and updated warning messages.
• src/playback.rs
  • Added a utility function playback_error_message to format user-friendly error messages for playback failures.
• src/tui/mod.rs
  • Refactored TUI playback state management with new helper functions, improved error handling for playback startup, and added a unit test for playback failure.
• src/tui/triage.rs
  • Modified triage mode playback initiation to use the new apply_playback_start_result function for consistent error handling.
• tests/cli.rs
  • Added a new CLI test case to verify the correct exit code and error message when attempting playback without mpv.

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[gemini-code-assist]

Code Review

This pull request effectively improves the handling of the mpv playback dependency. It introduces a 'fail fast' mechanism for the CLI, prevents the TUI from displaying misleading playback status on startup failure, and enhances the documentation regarding installation dependencies. The addition of regression and unit tests is a great way to ensure these fixes are robust. I have one suggestion to slightly refactor the new error handling function for better readability, aligning with our guidelines on reducing code duplication.