Define standardized exit codes

[joelhooks]

Problem

CLI currently uses generic exit codes. Agents and scripts can't distinguish between different failure modes.

Pattern from Go CLI Books

Standard Unix exit code conventions:

const (
    ExitSuccess           = 0   // Operation succeeded
    ExitGenericError      = 1   // Generic error
    ExitMisuse            = 2   // Wrong arguments, invalid flags
    ExitDataError         = 64  // Invalid input data format
    ExitTimeout           = 65  // Operation timed out
    ExitIOError           = 66  // Can't write to socket/file
    ExitProtocolError     = 67  // Invalid RPC response
    ExitDaemonUnavailable = 69  // Daemon not running
    ExitInternalError     = 70  // Panic, unexpected condition
)

Action Items

• Create internal/types/exitcodes.go with constants
• Update all command handlers to use specific exit codes
• Document exit codes in README and --help output
• Add exit code to JSON error output

Book References

• Search: pdf-brain search "exit code convention" --fts --expand 2000
• Search: pdf-brain search "os.Exit error handling" --fts --expand 2000

Priority

P1 - Important for agentic workflows