Create a vault whole in a temporary directory, then select it (closes #105)

vault.CreateVault takes the unlocker passphrase and writes the vault
directory, its metadata, long-term public key and passphrase unlocker
into a temporary directory, renames that into vaults.d once complete,
and only then makes the vault current. secret init and secret vault
create call it once instead of adding the unlocker afterwards, so a
kill part-way leaves either no vault, whose temporary directory the
next command that takes the lock deletes, or a complete one. A test
records the state directory before every change the call makes and
checks each state, and the command run again from it.

Model: opus-5-5

TODO.md

@@ -18,6 +18,19 @@ https://git.eeqj.de/sneak/secret/milestone/12
 
 # Completed Steps
 
+- 2026-10-04: `secret init` and `secret vault create` create a vault whole or
+  not at all (https://git.eeqj.de/sneak/secret/issues/105).
+  `vault.CreateVault` now takes the unlocker passphrase too, writes the vault
+  directory with its metadata, long-term public key and passphrase unlocker,
+  `longterm.age` included, into a temporary directory, renames that into
+  `vaults.d` once it is complete, and only then makes the vault current.
+  Before, either command killed after the passphrase prompt but before the
+  unlocker was written left a vault with no unlocker, which `vault create` had
+  already made current and which neither command would create again. Killed
+  part-way now, it leaves no vault, and the next command that takes the lock
+  deletes the temporary directory; or, killed between the rename and making
+  the vault current, a complete vault that is not current, which
+  `secret vault select` makes current.
 - 2026-10-04: What a command killed part-way left under a `.tmp-` name
   (https://git.eeqj.de/sneak/secret/issues/75), the temporary directories
   of `secret.TempDirFor` and the temporary files of
@@ -242,11 +255,7 @@ https://git.eeqj.de/sneak/secret/milestone/12
   `current-unlocker` never go missing. New versions, new secrets and
   cross-vault copies are built in a temporary directory and renamed
   into place, and removals rename out of the way first, so a version
-  or secret is never half-added and never half-removed. An
-  interrupted command can still leave, from `init` or `vault create`
-  killed after the passphrase prompt but before the unlocker is
-  written, a vault with no unlocker, which `vault create` has already
-  made the current vault.
+  or secret is never half-added and never half-removed.
 - 2026-10-03: The checks run before changing a vault now stop with an
   error naming the path and cause when they cannot read what they
   inspect, instead of reading the failure as "nothing there": the

internal/cli/confirm_test.go

@@ -63,10 +63,10 @@ func newConfirmTestVaults(
 	fs := &afero.MemMapFs{}
 	mnemonic := testMnemonicBuffer(t)
 
-	_, err := vault.CreateVault(fs, testStateDir, "other", mnemonic)
+	_, err := vault.CreateVault(fs, testStateDir, "other", mnemonic, nil)
 	require.NoError(t, err)
 
-	vlt, err := vault.CreateVault(fs, testStateDir, "work", mnemonic)
+	vlt, err := vault.CreateVault(fs, testStateDir, "work", mnemonic, nil)
 	require.NoError(t, err)
 
 	addTestSecret(t, vlt, []byte("older"), false)

internal/cli/create_vault_test.go

@@ -2,7 +2,11 @@ package cli_test
 
 import (
 	"bytes"
+	"io"
+	"maps"
 	"os"
+	"slices"
+	"strings"
 	"testing"
 
 	"git.eeqj.de/sneak/secret/internal/cli"
@@ -155,7 +159,7 @@ func TestStopAtPassphrasePromptLeavesNothing(t *testing.T) {
 	require.NoError(t, empty.MkdirAll(testStateDir, secret.DirPerms))
 
 	withDefault := afero.NewMemMapFs()
-	_, err := vault.CreateVault(withDefault, testStateDir, "default", mnemonic)
+	_, err := vault.CreateVault(withDefault, testStateDir, "default", mnemonic, nil)
 	require.NoError(t, err)
 
 	cmd := &cobra.Command{}
@@ -193,3 +197,192 @@ func TestStopAtPassphrasePromptLeavesNothing(t *testing.T) {
 		})
 	}
 }
+
+// TestStopDuringCreateLeavesWholeVaultOrNone is a regression test for
+// https://git.eeqj.de/sneak/secret/issues/105: `secret init` or `secret vault
+// create` killed after the passphrase prompt but before the unlocker was
+// written left a vault with no unlocker, which neither command would then
+// create again. After the prompt, each command changes the state directory
+// only through vault.CreateVault. The test makes that call as the command
+// does and records the state directory before each change it makes, and once
+// after it returns: what a stop at that point leaves. Each must hold either
+// no vault, and not name it current, or exactly the finished vault, which
+// opens with the passphrase through its current unlocker. The command run
+// again after a stop first takes the lock, which must delete what the stop
+// left under a temporary name. Running the command is slow, so it runs once
+// on each different state the lock leaves, and must create the vault there,
+// or refuse the one there.
+//
+//nolint:paralleltest // commands on the in-memory filesystem share one lock
+func TestStopDuringCreateLeavesWholeVaultOrNone(t *testing.T) {
+	mnemonic := testMnemonicBuffer(t)
+	passphrase := memguard.NewBufferFromBytes([]byte(testPassphrase))
+	t.Cleanup(passphrase.Destroy)
+
+	cmd := &cobra.Command{}
+	cmd.SetOut(io.Discard)
+
+	t.Run("init", func(t *testing.T) {
+		// From an empty state directory
+		fs := afero.NewMemMapFs()
+		require.NoError(t, fs.MkdirAll(testStateDir, secret.DirPerms))
+
+		requireStopsLeaveWholeVaultOrNone(t, fs, "default",
+			"failed to create default vault: vault default already exists",
+			mnemonic, passphrase,
+			func(c *cli.Instance) error { return c.Init(cmd) })
+	})
+
+	t.Run("vault create work", func(t *testing.T) {
+		// From a state directory holding the vault "default"
+		fs := afero.NewMemMapFs()
+		_, err := vault.CreateVault(fs, testStateDir, "default", mnemonic, nil)
+		require.NoError(t, err)
+
+		requireStopsLeaveWholeVaultOrNone(t, fs, "work", "vault work already exists",
+			mnemonic, passphrase,
+			func(c *cli.Instance) error { return c.CreateVault(cmd, "work") })
+	})
+}
+
+// requireStopsLeaveWholeVaultOrNone checks, as
+// TestStopDuringCreateLeavesWholeVaultOrNone describes, the stops of the
+// command run, creating the vault name on fs with mnemonic and passphrase.
+// Run again where the vault is there, the command must fail with exists.
+func requireStopsLeaveWholeVaultOrNone(
+	t *testing.T, fs afero.Fs, name, exists string,
+	mnemonic, passphrase *memguard.LockedBuffer,
+	run func(c *cli.Instance) error,
+) {
+	t.Helper()
+
+	var stops []map[string]string
+
+	record := func() { stops = append(stops, snapshotStateDir(t, fs)) }
+
+	_, err := vault.CreateVault(hookFs{Fs: fs, before: record},
+		testStateDir, name, mnemonic, passphrase)
+	require.NoError(t, err)
+	record()
+
+	vaultDir := testStateDir + "/vaults.d/" + name
+	require.NotContains(t, stops[0], vaultDir+"/", "no stop before the vault")
+
+	finished := entriesUnder(stops[len(stops)-1], vaultDir)
+
+	opener := vault.NewVault(fs, testStateDir, name)
+	opener.UnlockPassphrase = passphrase
+
+	key, err := opener.UnlockVault()
+	require.NoError(t, err)
+	require.Equal(t, finished[vaultDir+"/pub.age"], key.Recipient().String())
+
+	// Each different state the command run again finds once it holds the lock
+	var locked []map[string]string
+
+	for i, stop := range stops {
+		if _, there := stop[vaultDir+"/"]; there {
+			require.Equal(t, finished, entriesUnder(stop, vaultDir),
+				"stop %d left a partial vault", i)
+		} else {
+			require.NotEqual(t, name, stop[testStateDir+"/currentvault"],
+				"stop %d made a missing vault current", i)
+		}
+
+		stopped := newFsFromSnapshot(t, stop)
+		release, err := vault.LockStateDir(stopped, testStateDir)
+		require.NoError(t, err)
+		release()
+
+		state := snapshotStateDir(t, stopped)
+		for path := range state {
+			require.NotContains(t, path, ".tmp-", "stop %d", i)
+		}
+
+		if !slices.ContainsFunc(locked, func(s map[string]string) bool {
+			return maps.Equal(s, state)
+		}) {
+			locked = append(locked, state)
+		}
+	}
+
+	for _, state := range locked {
+		c := cli.NewCLIInstanceWithStateDir(newFsFromSnapshot(t, state), testStateDir)
+		c.Mnemonic = mnemonic
+		c.UnlockPassphrase = passphrase
+
+		if _, there := state[vaultDir+"/"]; there {
+			require.EqualError(t, run(c), exists)
+		} else {
+			require.NoError(t, run(c))
+		}
+	}
+}
+
+// entriesUnder returns the entries of a tree recorded by snapshotStateDir
+// that are under dir.
+func entriesUnder(tree map[string]string, dir string) map[string]string {
+	entries := map[string]string{}
+
+	for path, content := range tree {
+		if strings.HasPrefix(path, dir+"/") {
+			entries[path] = content
+		}
+	}
+
+	return entries
+}
+
+// hookFs passes every call through to Fs, but first calls before for each
+// call that can change the filesystem.
+type hookFs struct {
+	afero.Fs
+
+	before func()
+}
+
+//nolint:ireturn // implements afero.Fs
+func (h hookFs) Create(name string) (afero.File, error) {
+	h.before()
+
+	return h.Fs.Create(name)
+}
+
+//nolint:ireturn // implements afero.Fs
+func (h hookFs) OpenFile(
+	name string, flag int, perm os.FileMode,
+) (afero.File, error) {
+	h.before()
+
+	return h.Fs.OpenFile(name, flag, perm)
+}
+
+func (h hookFs) Mkdir(name string, perm os.FileMode) error {
+	h.before()
+
+	return h.Fs.Mkdir(name, perm)
+}
+
+func (h hookFs) MkdirAll(path string, perm os.FileMode) error {
+	h.before()
+
+	return h.Fs.MkdirAll(path, perm)
+}
+
+func (h hookFs) Remove(name string) error {
+	h.before()
+
+	return h.Fs.Remove(name)
+}
+
+func (h hookFs) RemoveAll(path string) error {
+	h.before()
+
+	return h.Fs.RemoveAll(path)
+}
+
+func (h hookFs) Rename(oldname, newname string) error {
+	h.before()
+
+	return h.Fs.Rename(oldname, newname)
+}

internal/cli/init.go

@@ -6,13 +6,10 @@ import (
 	"log"
 	"log/slog"
 	"os"
-	"path/filepath"
 	"strings"
 
-	"filippo.io/age"
 	"git.eeqj.de/sneak/secret/internal/secret"
 	"git.eeqj.de/sneak/secret/internal/vault"
-	"git.eeqj.de/sneak/secret/pkg/agehd"
 	"github.com/awnumar/memguard"
 	"github.com/spf13/cobra"
 	"github.com/tyler-smith/go-bip39"
@@ -70,43 +67,6 @@ func (cli *Instance) promptMnemonic() (*memguard.LockedBuffer, func(), error) {
 	return mnemonicBuffer, mnemonicBuffer.Destroy, nil
 }
 
-// setupDefaultVault creates the default vault and derives its long-term
-// identity from the mnemonic
-func (cli *Instance) setupDefaultVault(
-	stateDir string, mnemonic *memguard.LockedBuffer,
-) (*vault.Vault, *age.X25519Identity, error) {
-	// Create the default vault - it will handle key derivation internally
-	secret.Debug("Creating default vault")
-
-	vlt, err := vault.CreateVault(cli.fs, cli.stateDir, "default", mnemonic)
-	if err != nil {
-		secret.Debug("Failed to create default vault", "error", err)
-
-		return nil, nil, fmt.Errorf("failed to create default vault: %w", err)
-	}
-
-	// Get the vault metadata to retrieve the derivation index
-	vaultDir := filepath.Join(stateDir, "vaults.d", "default")
-
-	metadata, err := vault.LoadVaultMetadata(cli.fs, vaultDir)
-	if err != nil {
-		secret.Debug("Failed to load vault metadata", "error", err)
-
-		return nil, nil, fmt.Errorf("failed to load vault metadata: %w", err)
-	}
-
-	// Derive the long-term key using the same index that CreateVault used
-	ltIdentity, err := agehd.DeriveIdentity(mnemonic.String(), metadata.DerivationIndex)
-	if err != nil {
-		secret.Debug("Failed to derive long-term key", "error", err)
-
-		return nil, nil, fmt.Errorf(
-			"failed to derive long-term key from mnemonic: %w", err)
-	}
-
-	return vlt, ltIdentity, nil
-}
-
 // Init initializes the secret manager, holding the state directory lock
 // while initialize runs
 func (cli *Instance) Init(cmd *cobra.Command) error {
@@ -173,34 +133,31 @@ func (cli *Instance) initialize(cmd *cobra.Command) error {
 	}
 	defer cleanupPassphrase()
 
-	// Create the default vault and derive its long-term key
-	vlt, ltIdentity, err := cli.setupDefaultVault(stateDir, mnemonic)
+	// Create the default vault with its passphrase unlocker
+	secret.Debug("Creating default vault")
+
+	vlt, err := vault.CreateVault(cli.fs, cli.stateDir, "default",
+		mnemonic, passphraseBuffer)
+	if err != nil {
+		secret.Debug("Failed to create default vault", "error", err)
+
+		return fmt.Errorf("failed to create default vault: %w", err)
+	}
+
+	ltIdentity, err := vlt.GetOrDeriveLongTermKey()
+	if err != nil {
+		return fmt.Errorf("failed to get long-term key: %w", err)
+	}
+
+	unlocker, err := vlt.GetCurrentUnlocker()
 	if err != nil {
 		return err
 	}
 
-	ltPubKey := ltIdentity.Recipient().String()
-
-	// Unlock the vault with the derived long-term key
-	vlt.Unlock(ltIdentity)
-
-	// Create passphrase-protected unlocker
-	secret.Debug("Creating passphrase-protected unlocker")
-
-	passphraseUnlocker, err := vlt.CreatePassphraseUnlocker(passphraseBuffer)
-	if err != nil {
-		secret.Debug("Failed to create unlocker", "error", err)
-
-		return fmt.Errorf("failed to create unlocker: %w", err)
-	}
-
-	// Note: CreatePassphraseUnlocker already encrypts and writes the long-term
-	// private key to longterm.age, so no need to do it again here.
-
 	if cmd != nil {
 		cmd.Printf("\nDefault vault created and configured\n")
-		cmd.Printf("Long-term public key: %s\n", ltPubKey)
-		cmd.Printf("Unlocker ID: %s\n", passphraseUnlocker.GetID())
+		cmd.Printf("Long-term public key: %s\n", ltIdentity.Recipient().String())
+		cmd.Printf("Unlocker ID: %s\n", unlocker.GetID())
 		cmd.Println("\nYour secret manager is ready to use!")
 		cmd.Println("Note: When using SB_SECRET_MNEMONIC environment variable,")
 		cmd.Println("unlockers are not required for secret operations.")

internal/cli/integration_test.go

@@ -2563,7 +2563,7 @@ func secretRmCommand(ctx context.Context, t *testing.T) (*exec.Cmd, string) {
 	mnemonic := memguard.NewBufferFromBytes([]byte(testMnemonic))
 	defer mnemonic.Destroy()
 
-	vlt, err := vault.CreateVault(afero.NewOsFs(), stateDir, "default", mnemonic)
+	vlt, err := vault.CreateVault(afero.NewOsFs(), stateDir, "default", mnemonic, nil)
 	require.NoError(t, err)
 
 	value := memguard.NewBufferFromBytes([]byte("value"))

internal/cli/leftovers_test.go

@@ -28,7 +28,7 @@ func TestLeftoversRemovedByNextChangingCommand(t *testing.T) {
 
 	fs := newTwoVaultFs(t)
 
-	_, err := vault.CreateVault(fs, testStateDir, ".tmp-0", nil)
+	_, err := vault.CreateVault(fs, testStateDir, ".tmp-0", nil, nil)
 	require.NoError(t, err)
 	require.NoError(t, vault.SelectVault(fs, testStateDir, "default"))
 

internal/cli/lock_test.go

@@ -110,7 +110,7 @@ func TestConcurrentAddsKeepEveryVersion(t *testing.T) {
 		{"real", afero.NewOsFs(), t.TempDir()},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			_, err := vault.CreateVault(tc.fs, tc.stateDir, "default", mnemonic)
+			_, err := vault.CreateVault(tc.fs, tc.stateDir, "default", mnemonic, nil)
 			require.NoError(t, err)
 
 			// One add creates the secret; the others find that it exists
@@ -185,7 +185,7 @@ func (r *readNotifier) Read(p []byte) (int, error) {
 //nolint:paralleltest // times commands against the in-memory lock all tests share
 func TestEncryptPipedIntoAdd(t *testing.T) {
 	fs := afero.NewMemMapFs()
-	_, err := vault.CreateVault(fs, testStateDir, "default", testMnemonicBuffer(t))
+	_, err := vault.CreateVault(fs, testStateDir, "default", testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 	require.NoError(t, afero.WriteFile(fs, testInput, []byte("piped"), 0o600))
 
@@ -292,14 +292,14 @@ func setupEveryCommand(
 
 	mnemonic := testMnemonicBuffer(t)
 
-	other, err := vault.CreateVault(fs, testStateDir, "other", mnemonic)
+	other, err := vault.CreateVault(fs, testStateDir, "other", mnemonic, nil)
 	require.NoError(t, err)
 
 	otherDir, err := other.GetDirectory()
 	require.NoError(t, err)
 	require.NoError(t, fs.Remove(filepath.Join(otherDir, "pub.age")))
 
-	vlt, err := vault.CreateVault(fs, testStateDir, "work", mnemonic)
+	vlt, err := vault.CreateVault(fs, testStateDir, "work", mnemonic, nil)
 	require.NoError(t, err)
 
 	addTestSecret(t, vlt, []byte("older"), false)
@@ -487,7 +487,7 @@ func TestEncryptWithExistingKeyTakesNoLock(t *testing.T) {
 	mnemonic := testMnemonicBuffer(t)
 
 	fs := afero.NewMemMapFs()
-	_, err := vault.CreateVault(fs, testStateDir, "default", mnemonic)
+	_, err := vault.CreateVault(fs, testStateDir, "default", mnemonic, nil)
 	require.NoError(t, err)
 	require.NoError(t, afero.WriteFile(fs, testInput, []byte("input"), 0o600))
 
@@ -525,7 +525,7 @@ func TestEncryptWithExistingKeyTakesNoLock(t *testing.T) {
 //nolint:paralleltest // times commands against the in-memory lock all tests share
 func TestEncryptStreamsUnlocked(t *testing.T) {
 	fs := afero.NewMemMapFs()
-	_, err := vault.CreateVault(fs, testStateDir, "default", testMnemonicBuffer(t))
+	_, err := vault.CreateVault(fs, testStateDir, "default", testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 	require.NoError(t, afero.WriteFile(fs, testInput, []byte("streamed"), 0o600))
 

internal/cli/move_test.go

@@ -156,10 +156,10 @@ func TestMoveOntoSameSecretUnderAnotherNameIsRejected(t *testing.T) {
 			vaultsDir := filepath.Join(stateDir, "vaults.d")
 
 			// "default" is created last, so it is the current vault.
-			_, err := vault.CreateVault(fs, stateDir, "other", testMnemonicBuffer(t))
+			_, err := vault.CreateVault(fs, stateDir, "other", testMnemonicBuffer(t), nil)
 			require.NoError(t, err)
 
-			vlt, err := vault.CreateVault(fs, stateDir, "default", testMnemonicBuffer(t))
+			vlt, err := vault.CreateVault(fs, stateDir, "default", testMnemonicBuffer(t), nil)
 			require.NoError(t, err)
 
 			err = vlt.AddSecret("x", memguard.NewBufferFromBytes([]byte("value")), false)
@@ -205,7 +205,7 @@ func TestForcedCaseOnlyMoveOnCaseSensitiveFilesystem(t *testing.T) {
 	fs := afero.NewOsFs()
 	stateDir := t.TempDir()
 
-	vlt, err := vault.CreateVault(fs, stateDir, "default", testMnemonicBuffer(t))
+	vlt, err := vault.CreateVault(fs, stateDir, "default", testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	err = vlt.AddSecret("Foo", memguard.NewBufferFromBytes([]byte("upper")), false)

internal/cli/path_traversal_test.go

@@ -68,7 +68,7 @@ func newTwoVaultFs(t *testing.T) afero.Fs {
 		mnemonic := testMnemonicBuffer(t)
 
 		for _, name := range []string{"work", "default"} {
-			vlt, err := vault.CreateVault(fs, testStateDir, name, mnemonic)
+			vlt, err := vault.CreateVault(fs, testStateDir, name, mnemonic, nil)
 			require.NoError(t, err)
 
 			err = vlt.AddSecret("x", memguard.NewBufferFromBytes([]byte("value")), false)

internal/cli/secrets_size_test.go

@@ -71,7 +71,8 @@ func newSizeTestVault(t *testing.T) (afero.Fs, *vault.Vault) {
 	fs := afero.NewMemMapFs()
 
 	// Create vault
-	_, err := vault.CreateVault(fs, testStateDir, testVaultName, testMnemonicBuffer(t))
+	_, err := vault.CreateVault(fs, testStateDir, testVaultName,
+		testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	// Set current vault

internal/cli/unlockers_add_test.go

@@ -47,7 +47,7 @@ func TestAddPGPUnlocker(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			fs := afero.NewMemMapFs()
 			vlt, err := vault.CreateVault(fs, listTestStateDir, listTestVaultName,
-				testMnemonicBuffer(t))
+				testMnemonicBuffer(t), nil)
 			require.NoError(t, err)
 
 			err = vlt.AddSecret(addTestSecretName,

internal/cli/vault.go

@@ -293,40 +293,26 @@ func (cli *Instance) CreateVault(cmd *cobra.Command, name string) error {
 	}
 	defer cleanupPassphrase()
 
-	// Create the vault - it will handle key derivation internally
-	vlt, err := vault.CreateVault(cli.fs, cli.stateDir, name, mnemonic)
+	// Create the vault with its passphrase unlocker
+	vlt, err := vault.CreateVault(cli.fs, cli.stateDir, name,
+		mnemonic, passphraseBuffer)
 	if err != nil {
 		return err
 	}
 
-	// Get the vault metadata to retrieve the derivation index
-	vaultDir := filepath.Join(cli.stateDir, "vaults.d", name)
-
-	metadata, err := vault.LoadVaultMetadata(cli.fs, vaultDir)
+	ltIdentity, err := vlt.GetOrDeriveLongTermKey()
 	if err != nil {
-		return fmt.Errorf("failed to load vault metadata: %w", err)
+		return fmt.Errorf("failed to get long-term key: %w", err)
 	}
 
-	// Derive the long-term key using the same index that CreateVault used
-	ltIdentity, err := agehd.DeriveIdentity(mnemonicStr, metadata.DerivationIndex)
+	unlocker, err := vlt.GetCurrentUnlocker()
 	if err != nil {
-		return fmt.Errorf("failed to derive long-term key from mnemonic: %w", err)
-	}
-
-	// Unlock the vault with the derived long-term key
-	vlt.Unlock(ltIdentity)
-
-	// Create passphrase-protected unlocker
-	secret.Debug("Creating passphrase-protected unlocker")
-
-	passphraseUnlocker, err := vlt.CreatePassphraseUnlocker(passphraseBuffer)
-	if err != nil {
-		return fmt.Errorf("failed to create unlocker: %w", err)
+		return err
 	}
 
 	cmd.Printf("Created vault '%s'\n", vlt.GetName())
 	cmd.Printf("Long-term public key: %s\n", ltIdentity.Recipient().String())
-	cmd.Printf("Unlocker ID: %s\n", passphraseUnlocker.GetID())
+	cmd.Printf("Unlocker ID: %s\n", unlocker.GetID())
 
 	return nil
 }

internal/cli/version_test.go

@@ -73,7 +73,8 @@ func setupTestVault(t *testing.T, fs afero.Fs) {
 	t.Helper()
 
 	// Create vault
-	vlt, err := vault.CreateVault(fs, testStateDir, "default", testMnemonicBuffer(t))
+	vlt, err := vault.CreateVault(fs, testStateDir, "default",
+		testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	// Derive and store long-term key from mnemonic

internal/secret/atomic_test.go

@@ -235,7 +235,7 @@ func newVaultWithSecret(
 ) *vault.Vault {
 	t.Helper()
 
-	vlt, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t))
+	vlt, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	buffer := memguard.NewBufferFromBytes([]byte(value))
@@ -352,7 +352,7 @@ func TestLongestNames(t *testing.T) {
 	fs := afero.NewOsFs()
 	name := strings.Repeat("a", longestName)
 
-	vlt, err := vault.CreateVault(fs, t.TempDir(), name, testMnemonicBuffer(t))
+	vlt, err := vault.CreateVault(fs, t.TempDir(), name, testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	value := memguard.NewBufferFromBytes([]byte("long"))
@@ -646,7 +646,7 @@ func TestPassphraseUnlockerGetsKeyFirst(t *testing.T) {
 
 	// No mnemonic, and no current unlocker to get the key from
 	base := afero.NewMemMapFs()
-	_, err := vault.CreateVault(base, testVaultStateDir, testVaultName, nil)
+	_, err := vault.CreateVault(base, testVaultStateDir, testVaultName, nil, nil)
 	require.NoError(t, err)
 
 	fs := hookFs{Fs: base, before: func(_, path string) error {
@@ -678,7 +678,7 @@ func TestPassphraseUnlockerIsWholeOrAbsent(t *testing.T) {
 
 			base, stateDir := tfs.open(t)
 			vlt, err := vault.CreateVault(base, stateDir, testVaultName,
-				testMnemonicBuffer(t))
+				testMnemonicBuffer(t), nil)
 			require.NoError(t, err)
 
 			vaultDir, err := vlt.GetDirectory()
@@ -727,7 +727,7 @@ func TestPassphraseUnlockerReplacementKeepsVaultOpen(t *testing.T) {
 
 			base, stateDir := tfs.open(t)
 			vlt, err := vault.CreateVault(base, stateDir, testVaultName,
-				testMnemonicBuffer(t))
+				testMnemonicBuffer(t), nil)
 			require.NoError(t, err)
 
 			ltIdentity, err := vlt.GetOrDeriveLongTermKey()

internal/secret/pgpunlock_test.go

@@ -330,7 +330,7 @@ func testCreatePGPUnlocker(
 	mnemonic := testMnemonicBuffer(t)
 
 	// Create a test vault directory structure
-	vlt, err := vault.CreateVault(fs, stateDir, vaultName, mnemonic)
+	vlt, err := vault.CreateVault(fs, stateDir, vaultName, mnemonic, nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault: %v", err)
 	}

internal/secret/pgpunlocker_test.go

@@ -48,7 +48,7 @@ func TestCreatePGPUnlockerFailureWritesNothing(t *testing.T) {
 	installFakeGPG(t)
 
 	base := afero.NewMemMapFs()
-	vlt, err := vault.CreateVault(base, testVaultStateDir, testVaultName, nil)
+	vlt, err := vault.CreateVault(base, testVaultStateDir, testVaultName, nil, nil)
 	require.NoError(t, err)
 
 	fs := hookFs{Fs: base, before: func(_, path string) error {
@@ -87,7 +87,7 @@ func TestPGPUnlockerAddedTwiceKeepsFirst(t *testing.T) {
 
 	fs := afero.NewMemMapFs()
 	mnemonic := testMnemonicBuffer(t)
-	_, err := vault.CreateVault(fs, testVaultStateDir, testVaultName, mnemonic)
+	_, err := vault.CreateVault(fs, testVaultStateDir, testVaultName, mnemonic, nil)
 	require.NoError(t, err)
 
 	first, err := secret.CreatePGPUnlocker(

internal/vault/errors.go

@@ -31,6 +31,11 @@ var (
 	// Composed as "vault <name> already exists".
 	ErrVaultExists = errors.New("already exists")
 
+	// ErrUnlockerWithoutMnemonic indicates that CreateVault was given a
+	// passphrase for an unlocker but no mnemonic to derive the long-term key
+	// it unlocks. Composed as "vault <name> needs a mnemonic for an unlocker".
+	ErrUnlockerWithoutMnemonic = errors.New("needs a mnemonic for an unlocker")
+
 	// ErrNilValueBuffer indicates a nil value buffer was supplied.
 	ErrNilValueBuffer = errors.New("value buffer is nil")
 

internal/vault/integration_test.go

@@ -99,7 +99,7 @@ func testCurrentVaultFileHandling(t *testing.T, fs afero.Fs, tempDir string) {
 
 	// Create a test vault
 	vlt, err := vault.CreateVault(fs, stateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault: %v", err)
 	}
@@ -147,7 +147,7 @@ func testDeepPathSecrets(t *testing.T, fs afero.Fs, tempDir string) {
 	// Create a test vault - CreateVault writes the public key derived from
 	// the mnemonic
 	vlt, err := vault.CreateVault(fs, stateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault: %v", err)
 	}
@@ -223,7 +223,7 @@ func testKeyCaching(t *testing.T, fs afero.Fs, tempDir string) {
 	// Create a test vault - CreateVault writes the public key derived from
 	// the mnemonic
 	vlt, err := vault.CreateVault(fs, stateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault: %v", err)
 	}
@@ -324,7 +324,7 @@ func testVaultNameValidation(t *testing.T, fs afero.Fs, tempDir string) {
 	}
 
 	for _, name := range validNames {
-		_, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t))
+		_, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t), nil)
 		if err != nil {
 			t.Errorf("Failed to create vault with valid name %q: %v", name, err)
 		}
@@ -340,7 +340,7 @@ func testVaultNameValidation(t *testing.T, fs afero.Fs, tempDir string) {
 	}
 
 	for _, name := range invalidNames {
-		_, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t))
+		_, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t), nil)
 		if err == nil {
 			t.Errorf("Expected error creating vault with invalid name %q, "+
 				"but got none", name)
@@ -361,7 +361,7 @@ func testMultipleVaults(t *testing.T, fs afero.Fs, tempDir string) {
 	// Create three vaults
 	vaultNames := []string{"vault1", "vault2", "vault3"}
 	for _, name := range vaultNames {
-		_, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t))
+		_, err := vault.CreateVault(fs, stateDir, name, testMnemonicBuffer(t), nil)
 		if err != nil {
 			t.Fatalf("Failed to create vault %s: %v", name, err)
 		}
@@ -411,12 +411,12 @@ func testVaultIsolation(t *testing.T, fs afero.Fs, tempDir string) {
 
 	// Create two vaults - CreateVault writes the public key derived from
 	// the mnemonic
-	vault1, err := vault.CreateVault(fs, stateDir, "vault1", testMnemonicBuffer(t))
+	vault1, err := vault.CreateVault(fs, stateDir, "vault1", testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault1: %v", err)
 	}
 
-	vault2, err := vault.CreateVault(fs, stateDir, "vault2", testMnemonicBuffer(t))
+	vault2, err := vault.CreateVault(fs, stateDir, "vault2", testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault2: %v", err)
 	}

internal/vault/integration_version_test.go

@@ -49,7 +49,7 @@ func TestVersionIntegrationWorkflow(t *testing.T) {
 	fs := afero.NewMemMapFs()
 
 	// Create vault without a long-term key, which is set up below
-	vault, err := CreateVault(fs, testStateDir, "test", nil)
+	vault, err := CreateVault(fs, testStateDir, "test", nil, nil)
 	require.NoError(t, err)
 
 	// Derive and store long-term key from mnemonic

internal/vault/management.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 	"time"
 
+	"filippo.io/age"
 	"git.eeqj.de/sneak/secret/internal/secret"
 	"git.eeqj.de/sneak/secret/pkg/agehd"
 	"github.com/awnumar/memguard"
@@ -152,16 +153,17 @@ func ListVaults(fs afero.Fs, stateDir string) ([]string, error) {
 }
 
 // processMnemonicForVault handles mnemonic processing for vault creation.
-// It returns the derivation index, public key hash, and family hash.
+// It returns the long-term key, nil when there is no mnemonic, and the
+// derivation index, public key hash, and family hash.
 func processMnemonicForVault(
 	fs afero.Fs, stateDir, vaultDir, vaultName string,
 	mnemonicBuffer *memguard.LockedBuffer,
-) (uint32, string, string, error) {
+) (*age.X25519Identity, uint32, string, string, error) {
 	if mnemonicBuffer == nil {
 		secret.Debug("No mnemonic given, vault created without long-term key",
 			"vault", vaultName)
 		// Use 0 for derivation index when no mnemonic is provided
-		return 0, "", "", nil
+		return nil, 0, "", "", nil
 	}
 
 	mnemonic := mnemonicBuffer.String()
@@ -171,13 +173,14 @@ func processMnemonicForVault(
 	// Get the next available derivation index for this mnemonic
 	derivationIndex, err := GetNextDerivationIndex(fs, stateDir, mnemonic)
 	if err != nil {
-		return 0, "", "", fmt.Errorf("failed to get next derivation index: %w", err)
+		return nil, 0, "", "",
+			fmt.Errorf("failed to get next derivation index: %w", err)
 	}
 
 	// Derive the long-term key using the actual derivation index
 	ltIdentity, err := agehd.DeriveIdentity(mnemonic, derivationIndex)
 	if err != nil {
-		return 0, "", "", fmt.Errorf("failed to derive long-term key: %w", err)
+		return nil, 0, "", "", fmt.Errorf("failed to derive long-term key: %w", err)
 	}
 
 	// Write the public key
@@ -187,7 +190,8 @@ func processMnemonicForVault(
 
 	err = secret.WriteFileAtomic(fs, ltPubKeyPath, []byte(ltPubKey))
 	if err != nil {
-		return 0, "", "", fmt.Errorf("failed to write long-term public key: %w", err)
+		return nil, 0, "", "",
+			fmt.Errorf("failed to write long-term public key: %w", err)
 	}
 
 	secret.Debug("Wrote long-term public key", "path", ltPubKeyPath)
@@ -199,24 +203,33 @@ func processMnemonicForVault(
 	// This is used to identify which vaults belong to the same mnemonic family
 	identity0, err := agehd.DeriveIdentity(mnemonic, 0)
 	if err != nil {
-		return 0, "", "", fmt.Errorf("failed to derive identity for index 0: %w", err)
+		return nil, 0, "", "",
+			fmt.Errorf("failed to derive identity for index 0: %w", err)
 	}
 
 	familyHash := ComputeDoubleSHA256([]byte(identity0.Recipient().String()))
 
-	return derivationIndex, publicKeyHash, familyHash, nil
+	return ltIdentity, derivationIndex, publicKeyHash, familyHash, nil
 }
 
 // CreateVault creates a new vault and selects it as the current vault. When
 // mnemonic is not nil, the vault's long-term key is derived from it, and the
 // returned vault has it as its Mnemonic; when it is nil, the vault has no
-// long-term key until one is imported. It refuses a vault that already
-// exists before writing anything: creating it again would replace its keys,
-// and its secrets could no longer be decrypted. The commands that call it
-// hold the state directory lock, so no other command can create the vault
-// between the check and the writes.
+// long-term key until one is imported. When passphrase is not nil, the vault
+// gets a passphrase unlocker protected by it, as its current unlocker; that
+// needs a mnemonic. It refuses a vault that already exists before writing
+// anything: creating it again would replace its keys, and its secrets could
+// no longer be decrypted. The commands that call it hold the state directory
+// lock, so no other command can create the vault between the check and the
+// writes.
+//
+// The vault is written whole into a temporary directory, which is renamed
+// into vaults.d only once complete, and only then selected: a crash at any
+// point leaves either no vault or a complete one. The next command that
+// takes the lock deletes what the crash left under a temporary name.
 func CreateVault(
-	fs afero.Fs, stateDir string, name string, mnemonic *memguard.LockedBuffer,
+	fs afero.Fs, stateDir string, name string,
+	mnemonic, passphrase *memguard.LockedBuffer,
 ) (*Vault, error) {
 	secret.Debug("Creating new vault", "name", name, "state_dir", stateDir)
 
@@ -240,51 +253,19 @@ func CreateVault(
 		return nil, fmt.Errorf("vault %s %w", name, ErrVaultExists)
 	}
 
-	// Create vault directory structure
+	if passphrase != nil && mnemonic == nil {
+		return nil, fmt.Errorf("vault %s %w", name, ErrUnlockerWithoutMnemonic)
+	}
+
 	secret.Debug("Creating vault directory structure", "vault_dir", vaultDir)
 
-	// Create main vault directory
-	err = fs.MkdirAll(vaultDir, secret.DirPerms)
-	if err != nil {
-		return nil, fmt.Errorf("failed to create vault directory: %w", err)
-	}
-
-	// Create secrets directory
-	secretsDir := filepath.Join(vaultDir, "secrets.d")
-
-	err = fs.MkdirAll(secretsDir, secret.DirPerms)
-	if err != nil {
-		return nil, fmt.Errorf("failed to create secrets directory: %w", err)
-	}
-
-	// Create unlockers directory
-	unlockersDir := filepath.Join(vaultDir, "unlockers.d")
-
-	err = fs.MkdirAll(unlockersDir, secret.DirPerms)
-	if err != nil {
-		return nil, fmt.Errorf("failed to create unlockers directory: %w", err)
-	}
-
-	// Process mnemonic if available
-	derivationIndex, publicKeyHash, familyHash, err := processMnemonicForVault(
-		fs, stateDir, vaultDir, name, mnemonic)
+	err = secret.WriteDir(fs, vaultDir, func(dir string) error {
+		return writeVaultFiles(fs, stateDir, dir, name, mnemonic, passphrase)
+	})
 	if err != nil {
 		return nil, err
 	}
 
-	// Save vault metadata
-	metadata := &Metadata{
-		CreatedAt:          time.Now(),
-		DerivationIndex:    derivationIndex,
-		PublicKeyHash:      publicKeyHash,
-		MnemonicFamilyHash: familyHash,
-	}
-
-	err = SaveVaultMetadata(fs, vaultDir, metadata)
-	if err != nil {
-		return nil, fmt.Errorf("failed to save vault metadata: %w", err)
-	}
-
 	// Select the newly created vault as current
 	secret.Debug("Selecting newly created vault as current", "name", name)
 
@@ -302,6 +283,47 @@ func CreateVault(
 	return vlt, nil
 }
 
+// writeVaultFiles writes the files of the new vault name into vaultDir: its
+// secrets and unlockers directories, its long-term public key and metadata,
+// and, when passphrase is not nil, a passphrase unlocker as its current one.
+func writeVaultFiles(
+	fs afero.Fs, stateDir, vaultDir, name string,
+	mnemonic, passphrase *memguard.LockedBuffer,
+) error {
+	for _, subdir := range []string{"secrets.d", "unlockers.d"} {
+		err := fs.MkdirAll(filepath.Join(vaultDir, subdir), secret.DirPerms)
+		if err != nil {
+			return fmt.Errorf("failed to create %s directory: %w", subdir, err)
+		}
+	}
+
+	ltIdentity, derivationIndex, publicKeyHash, familyHash, err :=
+		processMnemonicForVault(fs, stateDir, vaultDir, name, mnemonic)
+	if err != nil {
+		return err
+	}
+
+	metadata := &Metadata{
+		CreatedAt:          time.Now(),
+		DerivationIndex:    derivationIndex,
+		PublicKeyHash:      publicKeyHash,
+		MnemonicFamilyHash: familyHash,
+	}
+
+	err = SaveVaultMetadata(fs, vaultDir, metadata)
+	if err != nil {
+		return fmt.Errorf("failed to save vault metadata: %w", err)
+	}
+
+	if passphrase == nil {
+		return nil
+	}
+
+	_, err = writePassphraseUnlocker(fs, vaultDir, ltIdentity, passphrase)
+
+	return err
+}
+
 // SelectVault selects the given vault as the current vault
 func SelectVault(fs afero.Fs, stateDir string, name string) error {
 	secret.Debug("Selecting vault", "vault_name", name, "state_dir", stateDir)

internal/vault/metadata_test.go

@@ -304,7 +304,7 @@ func TestWorkflowMismatch(t *testing.T) {
 	fs := afero.NewOsFs()
 
 	// Test Case 1: Create vault WITH mnemonic (like init command)
-	_, err := vault.CreateVault(fs, tempDir, "default", testMnemonicBuffer(t))
+	_, err := vault.CreateVault(fs, tempDir, "default", testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault with mnemonic: %v", err)
 	}
@@ -321,7 +321,7 @@ func TestWorkflowMismatch(t *testing.T) {
 		metadata1.DerivationIndex, metadata1.PublicKeyHash)
 
 	// Test Case 2: Create vault WITHOUT mnemonic, then import (work vault)
-	_, err = vault.CreateVault(fs, tempDir, "work", nil)
+	_, err = vault.CreateVault(fs, tempDir, "work", nil, nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault without mnemonic: %v", err)
 	}

internal/vault/path_traversal_test.go

@@ -18,7 +18,7 @@ func TestGetSecretVersionRejectsPathTraversal(t *testing.T) {
 	fs := afero.NewMemMapFs()
 
 	vlt, err := vault.CreateVault(fs, testStateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	// Add a legitimate secret so the vault is set up
@@ -57,7 +57,7 @@ func TestGetSecretRejectsPathTraversal(t *testing.T) {
 	fs := afero.NewMemMapFs()
 
 	vlt, err := vault.CreateVault(fs, testStateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	_, err = vlt.GetSecret("../../../etc/passwd")
@@ -73,7 +73,7 @@ func TestGetSecretObjectRejectsPathTraversal(t *testing.T) {
 	fs := afero.NewMemMapFs()
 
 	vlt, err := vault.CreateVault(fs, testStateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	require.NoError(t, err)
 
 	maliciousNames := []string{

internal/vault/secrets_version_test.go

@@ -66,7 +66,7 @@ func createTestVaultWithKey(t *testing.T, fs afero.Fs) *Vault {
 	t.Helper()
 
 	// Create vault without a long-term key, which is set up below
-	vault, err := CreateVault(fs, testStateDir, "test", nil)
+	vault, err := CreateVault(fs, testStateDir, "test", nil, nil)
 	require.NoError(t, err)
 
 	// Derive and store long-term key from mnemonic

internal/vault/unlockers.go

@@ -390,8 +390,31 @@ func (v *Vault) CreatePassphraseUnlocker(
 		return nil, err
 	}
 
+	unlocker, err := writePassphraseUnlocker(v.fs, vaultDir, ltIdentity, passphrase)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, oldDir := range oldDirs {
+		err = secret.RemoveDirAtomic(v.fs, oldDir)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"created and selected the new passphrase unlocker: %w", err)
+		}
+	}
+
+	return unlocker, nil
+}
+
+// writePassphraseUnlocker writes a new passphrase unlocker of the long-term
+// key ltIdentity into the vault directory vaultDir, in a directory of its own,
+// and makes it the vault's current unlocker.
+func writePassphraseUnlocker(
+	fs afero.Fs, vaultDir string, ltIdentity *age.X25519Identity,
+	passphrase *memguard.LockedBuffer,
+) (*secret.PassphraseUnlocker, error) {
 	createdAt := time.Now()
-	unlockerDir := filepath.Join(unlockersDir, unlockerTypePassphrase+"-"+
+	unlockerDir := filepath.Join(vaultDir, "unlockers.d", unlockerTypePassphrase+"-"+
 		createdAt.UTC().Format(secret.UnlockerTimeFormat))
 
 	// Generate new age keypair for unlocker
@@ -422,8 +445,8 @@ func (v *Vault) CreatePassphraseUnlocker(
 	}
 
 	// Write the unlocker's files, the metadata last
-	err = secret.WriteDir(v.fs, unlockerDir, func(dir string) error {
-		return v.writeUnlockerFiles(dir, unlockerIdentity, passphrase,
+	err = secret.WriteDir(fs, unlockerDir, func(dir string) error {
+		return writeUnlockerFiles(fs, dir, unlockerIdentity, passphrase,
 			encryptedLtPrivKey, metadataBytes)
 	})
 	if err != nil {
@@ -434,21 +457,13 @@ func (v *Vault) CreatePassphraseUnlocker(
 	// passphrase unlocker created in the same minute has the same ID.
 	currentUnlockerPath := filepath.Join(vaultDir, "current-unlocker")
 
-	err = secret.WriteFileAtomic(v.fs, currentUnlockerPath,
+	err = secret.WriteFileAtomic(fs, currentUnlockerPath,
 		[]byte(filepath.Base(unlockerDir)))
 	if err != nil {
 		return nil, fmt.Errorf("failed to select new unlocker: %w", err)
 	}
 
-	for _, oldDir := range oldDirs {
-		err = secret.RemoveDirAtomic(v.fs, oldDir)
-		if err != nil {
-			return nil, fmt.Errorf(
-				"created and selected the new passphrase unlocker: %w", err)
-		}
-	}
-
-	return secret.NewPassphraseUnlocker(v.fs, unlockerDir, metadata), nil
+	return secret.NewPassphraseUnlocker(fs, unlockerDir, metadata), nil
 }
 
 // passphraseUnlockerDirs returns the directories in unlockersDir that hold
@@ -514,7 +529,8 @@ func (v *Vault) readUnlockerMetadata(unlockerDir string) (UnlockerMetadata, erro
 // writeUnlockerFiles writes the files of a passphrase unlocker into
 // unlockerDir: its public key, its passphrase-encrypted private key, the
 // long-term private key encrypted to it, and its metadata, last.
-func (v *Vault) writeUnlockerFiles(
+func writeUnlockerFiles(
+	fs afero.Fs,
 	unlockerDir string,
 	unlockerIdentity *age.X25519Identity,
 	passphrase *memguard.LockedBuffer,
@@ -523,7 +539,7 @@ func (v *Vault) writeUnlockerFiles(
 	// Write public key
 	pubKeyPath := filepath.Join(unlockerDir, "pub.age")
 
-	err := secret.WriteFileAtomic(v.fs, pubKeyPath,
+	err := secret.WriteFileAtomic(fs, pubKeyPath,
 		[]byte(unlockerIdentity.Recipient().String()))
 	if err != nil {
 		return fmt.Errorf("failed to write unlocker public key: %w", err)
@@ -541,18 +557,18 @@ func (v *Vault) writeUnlockerFiles(
 	// Write encrypted private key
 	privKeyPath := filepath.Join(unlockerDir, "priv.age")
 
-	err = secret.WriteFileAtomic(v.fs, privKeyPath, encryptedPrivKey)
+	err = secret.WriteFileAtomic(fs, privKeyPath, encryptedPrivKey)
 	if err != nil {
 		return fmt.Errorf("failed to write encrypted unlocker private key: %w", err)
 	}
 
-	err = secret.WriteFileAtomic(v.fs,
+	err = secret.WriteFileAtomic(fs,
 		filepath.Join(unlockerDir, "longterm.age"), encryptedLtPrivKey)
 	if err != nil {
 		return fmt.Errorf("failed to write encrypted long-term private key: %w", err)
 	}
 
-	err = secret.WriteFileAtomic(v.fs,
+	err = secret.WriteFileAtomic(fs,
 		filepath.Join(unlockerDir, "unlocker-metadata.json"), metadataBytes)
 	if err != nil {
 		return fmt.Errorf("failed to write unlocker metadata: %w", err)

internal/vault/vault_test.go

@@ -2,6 +2,7 @@ package vault_test
 
 import (
 	"bytes"
+	"errors"
 	"path/filepath"
 	"slices"
 	"testing"
@@ -72,7 +73,7 @@ func testCreateVault(t *testing.T, fs afero.Fs) {
 	t.Helper()
 
 	vlt, err := vault.CreateVault(fs, testStateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault: %v", err)
 	}
@@ -298,7 +299,7 @@ func TestListUnlockers_SkipsMissingMetadata(t *testing.T) {
 
 	// Create vault
 	vlt, err := vault.CreateVault(fs, testStateDir, testVaultName,
-		testMnemonicBuffer(t))
+		testMnemonicBuffer(t), nil)
 	if err != nil {
 		t.Fatalf("Failed to create vault: %v", err)
 	}
@@ -344,3 +345,29 @@ func TestListUnlockers_SkipsMissingMetadata(t *testing.T) {
 		}
 	}
 }
+
+// TestCreateVaultUnlockerNeedsMnemonic checks that CreateVault, given a
+// passphrase for an unlocker but no mnemonic to derive the long-term key from,
+// fails without writing anything.
+func TestCreateVaultUnlockerNeedsMnemonic(t *testing.T) {
+	t.Parallel()
+
+	fs := afero.NewMemMapFs()
+
+	passphrase := memguard.NewBufferFromBytes([]byte(testPassphrase))
+	defer passphrase.Destroy()
+
+	_, err := vault.CreateVault(fs, testStateDir, testVaultName, nil, passphrase)
+	if !errors.Is(err, vault.ErrUnlockerWithoutMnemonic) {
+		t.Fatalf("Expected ErrUnlockerWithoutMnemonic, got %v", err)
+	}
+
+	exists, err := afero.Exists(fs, testStateDir)
+	if err != nil {
+		t.Fatalf("Failed to check for the state directory: %v", err)
+	}
+
+	if exists {
+		t.Errorf("CreateVault wrote the state directory")
+	}
+}