All blocks, every cluster.

Environment detection helpers: `isWsl`, `isCi`, `isHeadlessLinux`, `hasCommand`, `detectMode`, `shouldColor`. Shared across platform and agent blocks. Auto-installed as dependency.

Open a URL in the user's default browser across macOS, Linux, Windows, WSL, SSH, and headless CI. Respects `BROWSER` env var. Fallback chain with manual print. Never throws.

Copy text to the system clipboard across macOS, Linux (X11 + Wayland), Windows, and WSL. Detects `pbcopy`, `xclip`, `xsel`, `wl-copy`, `clip.exe` automatically. Typed verdict, never throws.

Fire a system notification across macOS (`osascript`), Linux (`notify-send`), Windows and WSL (PowerShell). Silently skips in CI. Typed verdict, never throws.

Terminal styling that respects NO_COLOR and non-TTY in one place, plus the width helpers a table needs once cells contain escape codes: visibleWidth, padVisible, truncateVisible. 256-color semantic palette.

Dual-rendering output for CLIs serving humans and agents. Auto-detects TTY vs piped, enforces `stdout`/`stderr` discipline, respects `NO_COLOR`. Never calls `process.exit()`.

Post-command guidance for agents and humans. Emit structured `next-step` hints to `stderr` as NDJSON for agents, formatted block for humans. Chains with `json-mode`.

Approval gate and structured preview renderer for T2/T3 CLI actions. Handles `--yes`, T3 `--confirm`, JSON/non-TTY refusal, and machine-readable AppError failures.

Health-check pattern for CLI `doctor` commands. Run named checks sequentially with per-check error isolation. Dual output via `json-mode`: structured JSON for agents, `[OK]`/`[FAIL]` table for humans.

Interactive first-run wizard for API-key-authenticated CLIs. Masked prompt, live validation against your API, then save via your callback. Generic over validator + save — no assumption about TOML/JSON/keychain storage. Throws typed errors, never calls `process.exit`. Extracted from v0-cli.

Post-init hook that offers to install a companion agent skill (Claude Code / Cursor / MCP-aware). Clack confirm plus a subprocess spawn with inherited stdio. Returns a discriminated outcome (`installed`, `cancelled`, `skipped`, `error`). Never throws.

Read a secret from the TTY without echoing it. Raw mode, one dot per keystroke, handles backspace and Ctrl-C. Returns null when there is no TTY so the caller can fail with a structured error instead of hanging. No runtime dependency.

XDG Base Directory Spec resolver with macOS (`~/Library`) and Windows (`%APPDATA%`) fallbacks. Gives your CLI canonical `config`/`state`/`cache`/`audit`/`sessions` paths. `APP_HOME` env override for testing.

Write files atomically: temp file, `fsync`, rename. Prevents corruption from crashes or concurrent CLI processes. Windows-aware (unlink before rename). Includes `atomicWriteJson` convenience.

Append-only JSONL audit trail with per-day rotation. Every action gets a timestamped record. Mode `0o600`. Includes `tailAudit` for reading recent records. Battle-tested in hapi-cli and sunat-cli.

Two-phase append-only audit lifecycle for dangerous or retryable operations: `beginAudit()` writes pending, then `complete()` or `fail()` appends the final record with the same audit id.

Gradient ASCII wordmark for your CLI. Shown on bare invoke or `--help`. Vertical gradient between two hex colors. Respects `NO_COLOR`. Includes minimal block-letter renderer.

Profile-aware JSON config loader. Reads from the app's config directory with multi-profile support (`--profile production`). Merge precedence: defaults < profile overrides.

Auth token persistence. Load on boot, save after login, clear on logout, check expiry. Atomic writes, `0o600` permissions. The companion of every `login` command.

Typed `AppError` class with `code`, `name`, `human` message, and `hint`. Maps upstream API errors to actionable messages. `fromHttp()` maps status codes directly. Agents read the `hint` field to self-correct.

Minimal POSIX argv parser for zero-framework CLIs. Zero dependencies. Handles `--flag`, `--flag value`, `--flag=value`, `-f`, combined short flags, positional args, `--` stop, and kebab-to-camelCase normalization.

Standard global flags for agent-first CLIs: `--json`, `--dry-run`, `--profile`, `--no-input`, `--quiet`, `--verbose`. Normalizes raw argv into typed `GlobalFlags`. Includes flag definitions for any parser.

Anonymous usage tracking. Opt-out via `CLI_NO_TELEMETRY=1` or `DO_NOT_TRACK=1`. Local JSONL logging + optional remote POST. Never throws, never blocks. Disabled in CI automatically.

Binary safety gate. If `~/.app/KILLSWITCH` exists, all write operations refuse. File exists = stopped. File gone = resumed. One `existsSync` call. Battle-tested in hapi-cli for real brokerage orders.