Commands fail when currentvault names no vault (closes #156)

An empty currentvault, or one naming a vault that does not exist, made
`secret list` report an empty vault with exit 0 and `secret add` fail on a
missing directory. ResolveVaultSymlink now refuses an empty or invalid
name, or one with no directory under vaults.d, with an error that wraps
ErrVaultNotFound, names the file and says to run
`secret vault select <name>`. Every command that uses the current vault
gets it; `secret vault list` still lists the vaults.

newSizeTestVault wrote a full path into currentvault, which resolved only
because the last path element was taken as the name; it now relies on
CreateVault selecting the vault.

Model: opus-5-5

internal/cli/current_vault_test.go

@@ -0,0 +1,59 @@
+package cli_test
+
+import (
+	"bytes"
+	"path/filepath"
+	"strconv"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/spf13/cobra"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/secret/internal/cli"
+	"sneak.berlin/go/secret/internal/secret"
+	"sneak.berlin/go/secret/internal/vault"
+)
+
+// TestListFailsWhenCurrentVaultDoesNotExist is a regression test for
+// https://git.eeqj.de/sneak/secret/issues/156, where a currentvault file
+// that was empty, or named a vault that does not exist, made `secret list`
+// report an empty vault. Listing must fail with an error that names the
+// file and says to run `secret vault select`, `secret vault list` must
+// still list the vaults, and selecting a vault must make listing work
+// again.
+func TestListFailsWhenCurrentVaultDoesNotExist(t *testing.T) {
+	t.Parallel()
+
+	for _, name := range []string{"", "gone"} {
+		t.Run(strconv.Quote(name), func(t *testing.T) {
+			t.Parallel()
+
+			fs := newTwoVaultFs(t)
+			currentVaultPath := filepath.Join(testStateDir, "currentvault")
+			require.NoError(t, afero.WriteFile(fs, currentVaultPath,
+				[]byte(name), secret.FilePerms))
+
+			c := cli.NewCLIInstanceWithStateDir(fs, testStateDir)
+
+			var out bytes.Buffer
+
+			cmd := &cobra.Command{}
+			cmd.SetOut(&out)
+
+			err := c.ListSecrets(cmd, false, true, "")
+			require.ErrorIs(t, err, vault.ErrVaultNotFound)
+			require.ErrorContains(t, err, currentVaultPath)
+			require.ErrorContains(t, err, "secret vault select")
+			assert.Empty(t, out.String())
+
+			require.NoError(t, c.ListVaults(cmd, false))
+			assert.Equal(t, "Available vaults:\n  default\n  work\n", out.String())
+
+			require.NoError(t, c.SelectVault(cmd, "default"))
+			out.Reset()
+			require.NoError(t, c.ListSecrets(cmd, false, true, ""))
+			assert.Equal(t, "x\n", out.String())
+		})
+	}
+}