Ask for the passphrase on the controlling terminal, not stdin (closes #144)

The passphrase and mnemonic prompts open /dev/tty and ask there, so
`echo v | secret add s1 --force`, `secret encrypt` and `secret decrypt`
with piped input ask at a terminal instead of failing. Only a process
with no controlling terminal still gets the error naming the variable to
set. `secret init` and `secret vault create` no longer write a newline
to stderr after the mnemonic.

On SIGINT or SIGTERM, Entry() restores the settings of /dev/tty instead
of stdin, since that is where the prompt turns echo off.

The two tests that pin the no-terminal message run the binary in a new
session, so it has no terminal wherever the tests run.

Unverified by a test: the echo restore after Ctrl-C, checked by hand.

Model: opus-5-5

README.md

@@ -374,8 +374,8 @@ variables.
 
 The prompt asks on the terminal the command runs in, not on stdin, so it also
 asks when stdin is a pipe, as in `echo value | secret add name --force` or
-`cat file | secret encrypt key`. With no terminal, as in a script or a CI job,
-the command fails and names the variable to set.
+`cat file | secret encrypt key`. With no controlling terminal, as under cron or
+in a CI job, the command fails and names the variable to set.
 
 ## Security Features
 

TODO.md

@@ -25,7 +25,9 @@ https://git.eeqj.de/sneak/secret/milestone/12
   (https://git.eeqj.de/sneak/secret/issues/144). Only a process with no
   controlling terminal gets the error that names the variable to set. On SIGINT
   or SIGTERM, `Entry()` restores the settings of that terminal, not of stdin,
-  since that is where the prompt turns echo off.
+  since that is where the prompt turns echo off. `secret init` and
+  `secret vault create` no longer write a newline to stderr after the mnemonic
+  is typed, since the prompt ends that line on the terminal.
 - 2026-10-14: A `secret add --force` that cannot unlock the vault, given a wrong
   passphrase or mnemonic, leaves the secret as it was
   (https://git.eeqj.de/sneak/secret/issues/136). The new version used to be

internal/cli/init.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"log"
 	"log/slog"
-	"os"
 	"strings"
 
 	"github.com/awnumar/memguard"
@@ -57,13 +56,11 @@ func (cli *Instance) promptMnemonic() (*memguard.LockedBuffer, func(), error) {
 	// Read mnemonic securely without echo
 	mnemonicBuffer, err := secret.ReadMnemonic("Enter your BIP39 mnemonic phrase: ")
 	if err != nil {
-		secret.Debug("Failed to read mnemonic from stdin", "error", err)
+		secret.Debug("Failed to read mnemonic", "error", err)
 
 		return nil, nil, err
 	}
 
-	fmt.Fprintln(os.Stderr) // Add newline after hidden input
-
 	return mnemonicBuffer, mnemonicBuffer.Destroy, nil
 }
 

internal/cli/passphrase_prompt_test.go

@@ -67,6 +67,77 @@ func TestPassphraseAskedAtTerminalWithPipedStdin(t *testing.T) {
 	assert.Equal(t, "a document\n", decrypted)
 }
 
+// TestInitWritesNoBlankLineAfterMnemonic runs `secret init 2>log` at a
+// terminal: the terminal is its controlling terminal and none of stdin,
+// stdout and stderr. The mnemonic is typed on the terminal and the prompt
+// ends its line there, so stderr must not get a newline for it as well, a
+// blank line in the log. pty.Open is described above
+// TestRemoveIgnoresTerminalOnStdout.
+func TestInitWritesNoBlankLineAfterMnemonic(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithTimeout(t.Context(), commandWait)
+	defer cancel()
+
+	stateDir := t.TempDir()
+
+	//nolint:gosec // G204: test executes the freshly built secret binary
+	cmd := exec.CommandContext(ctx, secretBinaryPath(t), "init")
+	cmd.Env = []string{
+		secret.EnvStateDir + "=" + stateDir,
+		secret.EnvUnlockPassphrase + "=" + testPassphrase,
+		"PATH=" + os.Getenv("PATH"),
+		"HOME=" + os.Getenv("HOME"),
+	}
+
+	ptmx, tty, err := pty.Open()
+	require.NoError(t, err)
+
+	defer func() { _ = ptmx.Close() }()
+
+	deadline, _ := ctx.Deadline()
+	require.NoError(t, ptmx.SetReadDeadline(deadline))
+
+	var stderr strings.Builder
+
+	cmd.Stderr = &stderr
+	cmd.ExtraFiles = []*os.File{tty}
+	// Ctty is a descriptor in the new process: 3, the first of ExtraFiles.
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true, Setctty: true, Ctty: 3}
+
+	require.NoError(t, cmd.Start())
+
+	_ = tty.Close()
+
+	var (
+		shown []byte
+		char  byte
+	)
+
+	terminal := bufio.NewReader(ptmx)
+	for !bytes.HasSuffix(shown, []byte("Enter your BIP39 mnemonic phrase: ")) {
+		char, err = terminal.ReadByte()
+		require.NoError(t, err, "secret init did not ask on the terminal: %s",
+			shown)
+
+		shown = append(shown, char)
+	}
+
+	_, err = ptmx.WriteString(testMnemonic + "\n")
+	require.NoError(t, err)
+
+	// The read ends once the command has exited and so closed the terminal.
+	rest, _ := io.ReadAll(terminal)
+
+	err = cmd.Wait()
+	require.NoError(t, err, "secret init: %s%s%s", shown, rest, stderr.String())
+
+	assert.True(t, strings.HasPrefix(stderr.String(),
+		"Initialized secrets manager at: "+stateDir+"\n\n"+
+			"Default vault created and configured\n"),
+		"stderr: %q", stderr.String())
+}
+
 // runAtTerminal runs the secret binary with args and input on stdin, in a
 // new session whose controlling terminal is a new terminal, which is also
 // its stderr: a command typed at a terminal with its input piped. pty.Open