Give each failure one error value (closes #113)

internal/cli's copies of vault.ErrSecretNotFound, ErrVaultNotFound,
ErrVersionNotFound and ErrSecretExists are removed; the commands wrap the
vault errors. Every error of secret.ReadPassphrase wraps
ErrPassphraseNotRead, so its callers no longer add those words.
ResolveGPGKeyFingerprint returns ErrGPGKeyNotFound for a key the keyring
lacks, recognised by gpg's status line. storeInKeychain returns
errNilDataBuffer. bip85's ErrPasswordTooShort and ErrEncodedTooShort go
with their unreachable checks. Tests that matched these errors' text use
errors.Is.

Model: opus-5-5

internal/cli/path_traversal_test.go

@@ -297,18 +297,8 @@ func TestInvalidVersionLeavesVaultsUnchanged(t *testing.T) {
 	for _, tt := range commands {
 		for _, version := range []string{"", ".", "..", "../../..", "a/b"} {
 			t.Run(fmt.Sprintf("%s %q", tt.command, version), func(t *testing.T) {
-				fs := newFsFromSnapshot(t, before)
-
-				err := tt.run(cli.NewCLIInstanceWithStateDir(fs, testStateDir), version)
-
-				require.Equal(t, before, snapshotStateDir(t, fs))
-
-				// Compared as text: `version rm` and `version promote` return
-				// internal/cli's own error of this text, which errors.Is does
-				// not match to vault.ErrVersionNotFound.
-				want := fmt.Errorf("version '%s' %w '%s'",
-					version, vault.ErrVersionNotFound, "x")
-				require.EqualError(t, err, want.Error())
+				requireRejectedAndUnchanged(t, before, vault.ErrVersionNotFound,
+					func(c *cli.Instance) error { return tt.run(c, version) })
 			})
 		}
 	}