Make the README's storage and file format text match the code (closes #102)

The directory tree shows `current` and `currentvault` as plain files holding
a name, a version's metadata as the encrypted `metadata.age`, the real state
directory under the user's configuration directory, and the `lock` file.
`version promote` rewrites `current`. File Formats tells unencrypted vault
and unlocker metadata from encrypted version metadata; `pub.age` is plain
text and vault metadata holds no vault name. Unlocker bullets lose Touch ID
claims the code does not set up, and the Secure Enclave only decrypts.
Per-version keys no longer claim forward secrecy. Testing lists only
`make test`.

Model: opus-5-5

TODO.md

@@ -29,6 +29,19 @@ https://git.eeqj.de/sneak/secret/milestone/12
   the Secure Enclave only decrypts; per-version keys give no forward
   secrecy; `pub.age` is not age-encrypted; vault metadata holds no vault
   name. Testing lists only `make test`.
+- 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: A failed `secret unlocker add keychain` or
   `secret unlocker add secure-enclave` no longer leaves its keychain item or
   Secure Enclave key behind (https://git.eeqj.de/sneak/secret/issues/89).
@@ -269,11 +282,7 @@ 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
+  or secret is never half-added and never half-removed.
-  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.
 - 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
+	// Create the default vault with its passphrase unlocker
-	vlt, ltIdentity, err := cli.setupDefaultVault(stateDir, mnemonic)
+	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("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())
 		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
+	// Create the vault with its passphrase unlocker
-	vlt, err := vault.CreateVault(cli.fs, cli.stateDir, name, mnemonic)
+	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
+	ltIdentity, err := vlt.GetOrDeriveLongTermKey()
-	vaultDir := filepath.Join(cli.stateDir, "vaults.d", name)
-
-	metadata, err := vault.LoadVaultMetadata(cli.fs, vaultDir)
 	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
+	unlocker, err := vlt.GetCurrentUnlocker()
-	ltIdentity, err := agehd.DeriveIdentity(mnemonicStr, metadata.DerivationIndex)
 	if err != nil {
-		return fmt.Errorf("failed to derive long-term key from mnemonic: %w", err)
+		return 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)
 	}
 
 	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

@@ -236,7 +236,7 @@ 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))
@@ -353,7 +353,7 @@ 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"))
@@ -647,7 +647,7 @@ 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 {
@@ -679,7 +679,7 @@ 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()
@@ -728,7 +728,7 @@ 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()
@@ -911,7 +911,7 @@ func TestSecureEnclaveUnlockerFailureDeletesKey(t *testing.T) {
 
 	mnemonic := testMnemonicBuffer(t)
 	base := afero.NewMemMapFs()
-	_, err := vault.CreateVault(base, testVaultStateDir, testVaultName, mnemonic)
+	_, err := vault.CreateVault(base, testVaultStateDir, testVaultName, mnemonic, nil)
 	require.NoError(t, err)
 
 	// The unlocker's directory is named se-<label of its Secure Enclave key>

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
+// long-term key until one is imported. When passphrase is not nil, the vault
-// exists before writing anything: creating it again would replace its keys,
+// gets a passphrase unlocker protected by it, as its current unlocker; that
-// and its secrets could no longer be decrypted. The commands that call it
+// needs a mnemonic. It refuses a vault that already exists before writing
-// hold the state directory lock, so no other command can create the vault
+// anything: creating it again would replace its keys, and its secrets could
-// between the check and the writes.
+// 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 = secret.WriteDir(fs, vaultDir, func(dir string) error {
-	err = fs.MkdirAll(vaultDir, secret.DirPerms)
+		return writeVaultFiles(fs, stateDir, dir, name, mnemonic, passphrase)
-	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)
 	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 {
+	err = secret.WriteDir(fs, unlockerDir, func(dir string) error {
-		return v.writeUnlockerFiles(dir, unlockerIdentity, passphrase,
+		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 {
+	return secret.NewPassphraseUnlocker(fs, unlockerDir, metadata), nil
-		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
 }
 
 // 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")
+	}
+}