Skeleton, mnemonic input, derivation, and the ssh pub and priv commands (closes #1)

The module, the script entrypoints and Makefile, Docker-only linting, the mnemonic sources in the specified order with their refusals, the BIP-85 derivation, and keyfunc ssh pub and priv with the README test vectors as tests. Two review rounds; the second passed with no findings.

Model: opus-5 (implementation and review); fable-5-1 (landing)

internal/cli/cli_test.go

@@ -0,0 +1,110 @@
+package cli_test
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"git.eeqj.de/sneak/keyfunc/internal/cli"
+	"git.eeqj.de/sneak/keyfunc/internal/derive"
+	"git.eeqj.de/sneak/keyfunc/internal/mnemonic"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/crypto/ssh"
+)
+
+// The two lines the README says the example mnemonic produces.
+const (
+	vectorZero = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIJZOtOczrc/7CQytc" +
+		"uFwt7s4r8KjkZWkwjLZWBaFKD+7"
+	vectorOne = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOEWY8+/gmHYVC4u0Y" +
+		"0I4FKs+eVUulTPHfk9VtXw1tMF"
+)
+
+// example returns the mnemonic the README gives its test vectors for:
+// eleven abandons and about.
+func example() string {
+	return strings.Repeat("abandon ", 11) + "about"
+}
+
+func TestTheReadmeTestVectors(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	require.Equal(t,
+		vectorZero+" keyfunc/ssh/0",
+		strings.TrimSpace(run(t, "ssh", "pub", "-n", "0")),
+	)
+	require.Equal(t,
+		vectorOne+" keyfunc/ssh/1",
+		strings.TrimSpace(run(t, "ssh", "pub", "-n", "1")),
+	)
+}
+
+func TestTheCommentCanBeChosen(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	line := strings.TrimSpace(run(t, "ssh", "pub", "--comment", "mine"))
+	require.Equal(t, vectorZero+" mine", line)
+}
+
+func TestThePrivateKeyMatchesThePublicOne(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	block := run(t, "ssh", "priv", "-n", "1")
+	require.True(t,
+		strings.HasPrefix(block, "-----BEGIN OPENSSH PRIVATE KEY-----"),
+	)
+
+	parsed, err := ssh.ParsePrivateKey([]byte(block))
+	require.NoError(t, err)
+
+	back := strings.TrimSpace(
+		string(ssh.MarshalAuthorizedKey(parsed.PublicKey())),
+	)
+	require.Equal(t, vectorOne, back)
+}
+
+func TestAnIndexWithNoHardenedChildIsRefused(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	out, err := execute(t, "ssh", "pub", "-n", "2147483648")
+	require.ErrorIs(t, err, derive.ErrIndexTooLarge)
+	require.Empty(t, out)
+}
+
+func TestTheMnemonicCommandIsUsed(t *testing.T) {
+	t.Setenv(mnemonic.Variable, "")
+
+	line := strings.TrimSpace(run(t,
+		"ssh", "pub",
+		"--mnemonic-command", "printf '%s\\n' '"+example()+"'",
+	))
+	require.Equal(t, vectorZero+" keyfunc/ssh/0", line)
+}
+
+// run executes the tool with the given arguments and returns what it
+// wrote to standard output.
+func run(t *testing.T, args ...string) string {
+	t.Helper()
+
+	out, err := execute(t, args...)
+	require.NoError(t, err)
+
+	return out
+}
+
+// execute runs the tool and returns both what it wrote and how it
+// ended.
+func execute(t *testing.T, args ...string) (string, error) {
+	t.Helper()
+
+	var out bytes.Buffer
+
+	root := cli.Root()
+	root.SetOut(&out)
+	root.SetErr(&out)
+	root.SetArgs(args)
+
+	err := root.ExecuteContext(t.Context())
+
+	return out.String(), err
+}