Check vault names in every command that takes one (closes #68)

A vault name may use only lowercase ASCII letters, digits, `.`, `-` and
`_`, and must not be empty, `.` or `..`; the error now states that rule.
`vault create`, `vault import`, `vault select`, `vault remove`, both
vault names of `mv` and shell completion of a `vault:secret` argument
check the name as typed before building any path from it. Before,
`vault import ..` wrote a long-term key and an unlocker into the state
directory itself, and `vault select ..` made that the current vault.

Model: opus-5-5

internal/cli/path_traversal_test.go

@@ -292,6 +292,58 @@ func TestInvalidVersionLeavesVaultsUnchanged(t *testing.T) {
 	}
 }
 
+// TestInvalidVaultNameLeavesStateUnchanged is a regression test for
+// https://git.eeqj.de/sneak/secret/issues/68, where
+// `secret vault import ..` wrote a long-term key and an unlocker into the
+// state directory itself, and `secret vault select ..` made it the current
+// vault. Each command that takes a vault name must reject an invalid one
+// before building a path from it. The mnemonic and the passphrase are set,
+// and moves and removals use --force, so that only the name check stands
+// in the way.
+//
+//nolint:paralleltest // newTwoVaultFs uses t.Setenv
+func TestInvalidVaultNameLeavesStateUnchanged(t *testing.T) {
+	before := snapshotStateDir(t, newTwoVaultFs(t))
+
+	t.Setenv(secret.EnvUnlockPassphrase, testPassphrase)
+
+	cmd := &cobra.Command{}
+
+	// Each command is a format with %q where the vault name goes.
+	commands := []struct {
+		command string
+		run     func(c *cli.Instance, name string) error
+	}{
+		{"vault create %q", func(c *cli.Instance, name string) error {
+			return c.CreateVault(cmd, name)
+		}},
+		{"vault import %q", func(c *cli.Instance, name string) error {
+			return c.VaultImport(cmd, name)
+		}},
+		{"vault select %q", func(c *cli.Instance, name string) error {
+			return c.SelectVault(cmd, name)
+		}},
+		{"vault remove --force %q", func(c *cli.Instance, name string) error {
+			return c.RemoveVault(cmd, name, true)
+		}},
+		{"mv --force %q:x work:x", func(c *cli.Instance, name string) error {
+			return c.MoveSecret(cmd, name+":x", "work:x", true)
+		}},
+		{"mv --force default:x %q:x", func(c *cli.Instance, name string) error {
+			return c.MoveSecret(cmd, "default:x", name+":x", true)
+		}},
+	}
+
+	for _, tt := range commands {
+		for _, name := range []string{"", ".", "..", "a/b"} {
+			t.Run(fmt.Sprintf(tt.command, name), func(t *testing.T) {
+				requireRejectedAndUnchanged(t, before, vault.ValidateVaultName(name),
+					func(c *cli.Instance) error { return tt.run(c, name) })
+			})
+		}
+	}
+}
+
 // TestRemoveVersionRemovesOnlyThatVersion checks that `secret version rm`
 // with a version that is not the current one removes that version and
 // changes nothing else.