logger/

Responsibility

Provides a minimal logging subsystem for TmuxAI using a process-global singleton logger.
Owns creation, configuration, and lifecycle of the application's log output file.
Exposes both instance methods ((*Logger).Info/Error/Debug) and package-level convenience functions (logger.Info/Error/Debug) for call sites.

Logger encapsulates:
- logFile *os.File (the writable destination file),
- logger *log.Logger (standard library logger with log.LstdFlags),
- mu sync.Mutex (serializes writes and close operations).
Package-level singleton state is instance *Logger with once sync.Once to guarantee one-time initialization.
Init() calls newLogger() exactly once via once.Do; GetInstance()/global helpers assume initialization may occur elsewhere.
File location strategy is deterministic: $HOME/.config/tmuxai/tmuxai.log, with MkdirAll for the directory and append/create mode for the file.
Logging calls prepend severity tags ([INFO], [ERROR], [DEBUG]) to formatted messages and delegate to log.Logger.Printf.

Init → once.Do → newLogger:
1. Resolve $HOME via os.UserHomeDir.
2. Ensure ~/.config/tmuxai exists.
3. Open tmuxai.log with append/create/write flags.
4. Construct log.Logger and assign to global instance.
GetInstance returns an error if instance == nil (not initialized).
Package-level Info/Error/Debug functions check instance != nil and forward to the singleton instance methods; otherwise they no-op.
Instance Info/Error/Debug lock mu, format+print to file-backed logger, then unlock.
Close locks mu and closes logFile.

Imported by application entrypoints/components that need runtime log emission.
Consumers should call logger.Init() during startup before first logging; after that use either:
- package-level logger.Info(...) etc. (simplest), or
- logger.GetInstance() to obtain explicit *Logger when dependency-injected usage is desired.
The log file path (~/.config/tmuxai/tmuxai.log) is the primary external integration surface for operators and diagnostics tooling.