The age commands: pub, priv, encrypt and decrypt (closes #3)

keyfunc age derives an age identity at the generic path the way secret's agehd does, prints the recipient or the identity, and encrypts to or decrypts with it, the derived recipient always among encrypt's recipients. Two review rounds; the second passed with no findings, the clamping step now pinned by a fixed identity test.

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

internal/cli/age_test.go

@@ -0,0 +1,102 @@
+package cli_test
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.eeqj.de/sneak/keyfunc/internal/agekey"
+	"git.eeqj.de/sneak/keyfunc/internal/mnemonic"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTheAgeCommandsPrintTheKey(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	recipient := strings.TrimSpace(run(t, "age", "pub"))
+	require.True(t, strings.HasPrefix(recipient, "age1"))
+
+	identity := strings.TrimSpace(run(t, "age", "priv"))
+	require.True(t, strings.HasPrefix(identity, "AGE-SECRET-KEY-1"))
+}
+
+func TestAFileEncryptedByTheToolIsReadBackByIt(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+	sealed := filepath.Join(t.TempDir(), "notes.age")
+
+	run(t, "age", "encrypt", "-o", sealed, plain)
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", sealed))
+}
+
+func TestTheArmoredFormIsTextThatDecrypts(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+
+	armored := run(t, "age", "encrypt", "--armor", plain)
+	require.True(t, strings.HasPrefix(
+		armored, "-----BEGIN AGE ENCRYPTED FILE-----",
+	))
+
+	sealed := written(t, "notes.age", armored)
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", sealed))
+}
+
+func TestAnotherRecipientIsAddedAndTheDerivedOneStays(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	theirs := strings.TrimSpace(run(t, "age", "pub", "-n", "7"))
+	plain := written(t, "notes.txt", "the secret\n")
+	sealed := filepath.Join(t.TempDir(), "notes.age")
+
+	run(t, "age", "encrypt", "--to", theirs, "-o", sealed, plain)
+
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", sealed))
+	require.Equal(t,
+		"the secret\n", run(t, "age", "decrypt", "-n", "7", sealed),
+	)
+}
+
+func TestAFileForAnotherKeyIsRefused(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+	sealed := filepath.Join(t.TempDir(), "notes.age")
+
+	run(t, "age", "encrypt", "-n", "7", "-o", sealed, plain)
+
+	_, err := execute(t, "age", "decrypt", sealed)
+	require.ErrorIs(t, err, agekey.ErrNotRecipient)
+}
+
+func TestARefusedDecryptionLeavesTheOutputFileAlone(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+	sealed := filepath.Join(t.TempDir(), "notes.age")
+	existing := written(t, "notes.out", "what was already there\n")
+
+	run(t, "age", "encrypt", "-n", "7", "-o", sealed, plain)
+
+	_, err := execute(t, "age", "decrypt", "-o", existing, sealed)
+	require.ErrorIs(t, err, agekey.ErrNotRecipient)
+
+	//nolint:gosec // the test made this path itself
+	kept, err := os.ReadFile(existing)
+	require.NoError(t, err)
+	require.Equal(t, "what was already there\n", string(kept))
+}
+
+// written puts the contents in a file of that name in a directory of
+// this test's own and returns the path to it.
+func written(t *testing.T, name, contents string) string {
+	t.Helper()
+
+	path := filepath.Join(t.TempDir(), name)
+	require.NoError(t, os.WriteFile(path, []byte(contents), 0o600))
+
+	return path
+}