State-of-the-art CLI and developer-tool UX guidance (2026) covering command and flag design, output and interaction (stdout/stderr, --json, TTY detection, exit codes, prompts), runtime behavior and lifecycle (signals, dry-run, idempotency, XDG paths, completions, telemetry), and distribution (packag
State-of-the-art CLI and developer-tool UX guidance (2026) covering command and flag design, output and interaction (stdout/stderr, --json, TTY detection, exit codes, prompts), runtime behavior and lifecycle (signals, dry-run, idempotency, XDG paths, completions, telemetry), and distribution (packaging, checksums, docs). Use when designing or building any command line tool, subcommand, TUI, or dev