Other: Wipe vault properly on factory reset

Deleting the file isn't enough because it's still held in memory
and is written back to disk on the next write (SetLastVersion during
bridge teardown).

internal/vault/vault.go

@@ -185,6 +185,12 @@ func (vault *Vault) SetMigrated() error {
 	})
 }
 
+func (vault *Vault) Reset(gluonDir string) error {
+	return vault.mod(func(data *Data) {
+		*data = newDefaultData(gluonDir)
+	})
+}
+
 func (vault *Vault) Close() error {
 	vault.refLock.Lock()
 	defer vault.refLock.Unlock()

internal/vault/vault_test.go

@@ -77,6 +77,25 @@ func TestVault_Corrupt_JunkData(t *testing.T) {
 	}
 }
 
+func TestVault_Reset(t *testing.T) {
+	s := newVault(t)
+
+	// Write some data.
+	require.NoError(t, s.SetIMAPPort(1234))
+	require.NoError(t, s.SetSMTPPort(5678))
+
+	// The data was written.
+	require.Equal(t, 1234, s.GetIMAPPort())
+	require.Equal(t, 5678, s.GetSMTPPort())
+
+	// Reset.
+	require.NoError(t, s.Reset(s.GetGluonDir()))
+
+	// The data is gone.
+	require.Equal(t, 1143, s.GetIMAPPort())
+	require.Equal(t, 1025, s.GetSMTPPort())
+}
+
 func newVault(t *testing.T) *vault.Vault {
 	t.Helper()