Fix TUI startup foreground tty race (closes #31)

go.mod

@@ -21,6 +21,7 @@ require (
 	github.com/charmbracelet/log v1.0.0
 	github.com/go-logfmt/logfmt v0.6.1 // indirect
 	golang.org/x/exp v0.0.0-20231006140011-7918f672742d // indirect
+	golang.org/x/sys v0.38.0
 )
 
 require (
@@ -53,7 +54,6 @@ require (
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
 	golang.org/x/mod v0.29.0 // indirect
 	golang.org/x/sync v0.18.0 // indirect
-	golang.org/x/sys v0.38.0 // indirect
 	golang.org/x/text v0.30.0 // indirect
 	golang.org/x/tools v0.38.0 // indirect
 	gopkg.in/natefinch/lumberjack.v2 v2.2.1 // indirect

internal/statusui/statusui.go

@@ -2,6 +2,7 @@ package statusui
 
 import (
 	"context"
+	"errors"
 	"log/slog"
 	"os"
 
@@ -15,6 +16,19 @@ import (
 // cancelled or the user presses q. buf may be nil (log pane disabled).
 // cancelFn is called when the user presses x to kill the selected session; nil disables it.
 func Run(ctx context.Context, snap func() server.StateSnapshot, buf *logbuffer.Buffer, cfg Config, cancelFn func(string) bool) {
+	if err := waitForForegroundTTY(ctx); err != nil {
+		switch {
+		case errors.Is(err, context.Canceled), errors.Is(err, context.DeadlineExceeded):
+			return
+		case errors.Is(err, errNoControllingTTY):
+			slog.Info("statusui: no controlling tty; terminal UI disabled", "error", err)
+			return
+		default:
+			slog.Warn("statusui: foreground tty check failed; terminal UI disabled", "error", err)
+			return
+		}
+	}
+
 	m := New(snap, buf, cfg, cancelFn)
 	p := tea.NewProgram(m,
 		tea.WithOutput(os.Stderr),

internal/statusui/tty_foreground_other.go

@@ -0,0 +1,14 @@
+//go:build !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !solaris && !aix && !zos
+
+package statusui
+
+import (
+	"context"
+	"errors"
+)
+
+var errNoControllingTTY = errors.New("statusui: no controlling tty")
+
+func waitForForegroundTTY(context.Context) error {
+	return nil
+}

internal/statusui/tty_foreground_unix.go

@@ -0,0 +1,61 @@
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || aix || zos
+
+package statusui
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+var errNoControllingTTY = errors.New("statusui: no controlling tty")
+
+const foregroundTTYCheckInterval = 10 * time.Millisecond
+
+func waitForForegroundTTY(ctx context.Context) error {
+	tty, err := os.Open("/dev/tty")
+	if err != nil {
+		return fmt.Errorf("%w: %w", errNoControllingTTY, err)
+	}
+	defer tty.Close() //nolint:errcheck
+
+	return waitForForegroundProcessGroup(
+		ctx,
+		unix.Getpgrp,
+		func() (int, error) {
+			return unix.IoctlGetInt(int(tty.Fd()), unix.TIOCGPGRP)
+		},
+		foregroundTTYCheckInterval,
+	)
+}
+
+func waitForForegroundProcessGroup(
+	ctx context.Context,
+	currentPGID func() int,
+	foregroundPGID func() (int, error),
+	interval time.Duration,
+) error {
+	if interval <= 0 {
+		interval = foregroundTTYCheckInterval
+	}
+
+	for {
+		foreground, err := foregroundPGID()
+		if err != nil {
+			return fmt.Errorf("statusui: foreground process group: %w", err)
+		}
+		if foreground == currentPGID() {
+			return nil
+		}
+
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-time.After(interval):
+		}
+	}
+}

internal/statusui/tty_foreground_unix_test.go

@@ -0,0 +1,73 @@
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || aix || zos
+
+package statusui
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestWaitForForegroundProcessGroupReturnsImmediatelyWhenForeground(t *testing.T) {
+	var calls int
+	err := waitForForegroundProcessGroup(
+		context.Background(),
+		func() int { return 42 },
+		func() (int, error) {
+			calls++
+			return 42, nil
+		},
+		time.Millisecond,
+	)
+
+	require.NoError(t, err)
+	require.Equal(t, 1, calls)
+}
+
+func TestWaitForForegroundProcessGroupPollsUntilForeground(t *testing.T) {
+	var calls int
+	err := waitForForegroundProcessGroup(
+		context.Background(),
+		func() int { return 42 },
+		func() (int, error) {
+			calls++
+			if calls < 3 {
+				return 7, nil
+			}
+			return 42, nil
+		},
+		time.Millisecond,
+	)
+
+	require.NoError(t, err)
+	require.Equal(t, 3, calls)
+}
+
+func TestWaitForForegroundProcessGroupExitsOnContextCancel(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	err := waitForForegroundProcessGroup(
+		ctx,
+		func() int { return 42 },
+		func() (int, error) { return 7, nil },
+		time.Millisecond,
+	)
+
+	require.ErrorIs(t, err, context.Canceled)
+}
+
+func TestWaitForForegroundProcessGroupReturnsForegroundError(t *testing.T) {
+	want := errors.New("ioctl failed")
+	err := waitForForegroundProcessGroup(
+		context.Background(),
+		func() int { return 42 },
+		func() (int, error) { return 0, want },
+		time.Millisecond,
+	)
+
+	require.ErrorIs(t, err, want)
+}