Reject invalid secret names before any command builds a path (closes #33)

`secret rm ..` resolved to the vault directory and deleted the whole
vault; `secret rm .` and `secret rm ""` deleted every secret. rm, mv,
the version commands, encrypt and decrypt built paths from the name
without checking it; import checked it only after reading the source
file.

vault.ValidateSecretName wraps the existing name rule and its error
states the rule. Each of those commands calls it on the name as given,
before building any path; a move checks both names before switching
the current vault. AddSecret, GetSecretVersion and GetSecretObject use
it too.

The regression test copies two in-memory vaults for each rejected
command and requires the exact error and an unchanged state directory.

Model: opus-5-5

internal/cli/path_traversal_test.go

@@ -118,14 +118,32 @@ func newFsFromSnapshot(t *testing.T, tree map[string]string) afero.Fs {
 	return fs
 }
 
+// requireRejectedAndUnchanged runs a command on a copy of the state
+// directory recorded in before. It requires exactly the error
+// vault.ValidateSecretName gives for the rejected name, so that a later
+// check rejecting the name does not count, and everything under the state
+// directory as it was: the error alone proves nothing, since it could come
+// after the vault had already been deleted.
+func requireRejectedAndUnchanged(
+	t *testing.T, before map[string]string, rejected string,
+	run func(c *cli.Instance) error,
+) {
+	t.Helper()
+
+	fs := newFsFromSnapshot(t, before)
+
+	err := run(cli.NewCLIInstanceWithStateDir(fs, testStateDir))
+
+	require.Equal(t, before, snapshotStateDir(t, fs))
+	require.ErrorIs(t, err, vault.ErrInvalidSecretName)
+	require.EqualError(t, err, vault.ValidateSecretName(rejected).Error())
+}
+
 // TestInvalidSecretNameLeavesVaultsUnchanged is a regression test for
 // https://git.eeqj.de/sneak/secret/issues/33, where `secret rm ..` deleted
 // the whole vault, and `secret rm .` or `secret rm ""` every secret in it.
-// Each command must fail with exactly the error vault.ValidateSecretName
-// gives for the name, and leave everything under the state directory as it
-// was: the error alone proves nothing, since it could come after the vault
-// had already been deleted. Moves and imports use --force, so that only
-// the name check stands in the way.
+// Moves and imports use --force, so that only the name check stands in
+// the way.
 //
 //nolint:paralleltest // newTwoVaultFs uses t.Setenv
 func TestInvalidSecretNameLeavesVaultsUnchanged(t *testing.T) {
@@ -208,13 +226,7 @@ func TestInvalidSecretNameLeavesVaultsUnchanged(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.command, func(t *testing.T) {
-			fs := newFsFromSnapshot(t, before)
-
-			err := tt.run(cli.NewCLIInstanceWithStateDir(fs, testStateDir))
-
-			require.Equal(t, before, snapshotStateDir(t, fs))
-			require.ErrorIs(t, err, vault.ErrInvalidSecretName)
-			require.EqualError(t, err, vault.ValidateSecretName(tt.rejected).Error())
+			requireRejectedAndUnchanged(t, before, tt.rejected, tt.run)
 		})
 	}
 }