feat: golang-cli v1.0.0 — generic command-tree CLI library

Reusable, generics-based CLI extracted from vpp-evpn's cmd/evpnc:
a declarative command tree (Node[C]) from which dispatch, '?'-help and
TAB-completion are derived, an interactive Shell[C], dynamic slot
resolvers (context-dependent via captured args), text-or-JSON output
(Emit), and color helpers (Paint/Label/KV). Builds on Linux and OpenBSD
(readline termios override). Includes a self-contained example and a
design proposal under docs/.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

term_openbsd.go

@@ -0,0 +1,68 @@
+// SPDX-FileCopyrightText: (C) Copyright 2026 Pim van Pelt <pim@ipng.ch>
+// SPDX-License-Identifier: Apache-2.0
+
+//go:build openbsd
+
+package cli
+
+import (
+	"os"
+
+	"github.com/chzyer/readline"
+	"golang.org/x/sys/unix"
+)
+
+// applyTermFuncs makes readline drive the terminal through golang.org/x/sys/unix.
+//
+// chzyer/readline's own termios handling (term_bsd.go) issues raw
+// syscall.Syscall6(SYS_IOCTL, ...) calls. OpenBSD forbids direct syscalls from
+// outside libc, so those return ENOSYS: readline's IsTerminal() then reports
+// false and the REPL silently degrades to a dumb line reader -- no prompt, no
+// tab completion. x/sys/unix performs the same ioctls through libc.
+//
+// The raw-mode flag set below is copied verbatim from readline's own MakeRaw
+// (term.go), and that match matters: it deliberately leaves OPOST enabled, so a
+// command's "\n" output is still translated to "\r\n". A full cfmakeraw (e.g.
+// golang.org/x/term.MakeRaw) clears OPOST and staircases multi-line output.
+// Only OpenBSD needs this; every other platform keeps readline's native path.
+func applyTermFuncs(cfg *readline.Config) {
+	stdin := int(os.Stdin.Fd())
+	stdout := int(os.Stdout.Fd())
+	var saved *unix.Termios
+
+	cfg.FuncIsTerminal = func() bool {
+		_, err := unix.IoctlGetTermios(stdin, unix.TIOCGETA)
+		return err == nil
+	}
+	cfg.FuncMakeRaw = func() error {
+		old, err := unix.IoctlGetTermios(stdin, unix.TIOCGETA)
+		if err != nil {
+			return err
+		}
+		saved = old
+		raw := *old
+		raw.Iflag &^= unix.IGNBRK | unix.BRKINT | unix.PARMRK | unix.ISTRIP | unix.INLCR | unix.IGNCR | unix.ICRNL | unix.IXON
+		// OPOST is intentionally left set (see the doc comment above).
+		raw.Lflag &^= unix.ECHO | unix.ECHONL | unix.ICANON | unix.ISIG | unix.IEXTEN
+		raw.Cflag &^= unix.CSIZE | unix.PARENB
+		raw.Cflag |= unix.CS8
+		raw.Cc[unix.VMIN] = 1
+		raw.Cc[unix.VTIME] = 0
+		return unix.IoctlSetTermios(stdin, unix.TIOCSETA, &raw)
+	}
+	cfg.FuncExitRaw = func() error {
+		if saved == nil {
+			return nil
+		}
+		err := unix.IoctlSetTermios(stdin, unix.TIOCSETA, saved)
+		saved = nil
+		return err
+	}
+	cfg.FuncGetWidth = func() int {
+		ws, err := unix.IoctlGetWinsize(stdout, unix.TIOCGWINSZ)
+		if err != nil || ws.Col == 0 {
+			return 80 // sane default when the width can't be read
+		}
+		return int(ws.Col)
+	}
+}