fix: isolate parent exit watcher environment (#2256)

Author: yohamta0

internal/cmn/cmdutil/parent_exit_watcher_unix.go

@@ -31,6 +31,8 @@ func StartParentExitWatcher(cmd *exec.Cmd) (func(), error) {
 	const script = `if IFS= read -r line <&3 && [ "$line" = "` + parentExitWatcherOK + `" ]; then exit 0; fi; kill -KILL -"$1" 2>/dev/null; exit 0`
 	watcher := exec.Command("/bin/sh", "-c", script, "dagu-parent-exit-watcher", strconv.Itoa(cmd.Process.Pid)) //nolint:gosec
 	watcher.ExtraFiles = []*os.File{readPipe}
+	// Keep shell control variables from changing the watcher's blocking read.
+	watcher.Env = []string{"PATH=/usr/bin:/bin"}
 	setupCommand(watcher)
 
 	if err := watcher.Start(); err != nil {

internal/cmn/cmdutil/parent_exit_watcher_unix_external_test.go

@@ -0,0 +1,83 @@
+// Copyright (C) 2026 Yota Hamada
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build !windows
+
+package cmdutil_test
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"syscall"
+	"testing"
+	"time"
+
+	"github.com/dagucloud/dagu/internal/cmn/cmdutil"
+	"github.com/stretchr/testify/require"
+)
+
+const parentExitWatcherHelperEnv = "DAGU_PARENT_EXIT_WATCHER_HELPER"
+
+func TestParentExitWatcherIgnoresInheritedShellTimeout(t *testing.T) {
+	t.Setenv("TMOUT", "1")
+
+	cmd := exec.Command("/bin/sh", "-c", "sleep 2") //nolint:gosec
+	cmd.Env = []string{"PATH=/usr/bin:/bin"}
+
+	startedAt := time.Now()
+	proc, err := cmdutil.StartManagedProcess(cmd)
+	require.NoError(t, err)
+	defer func() { _ = proc.Release() }()
+
+	require.NoError(t, proc.Wait())
+	require.GreaterOrEqual(t, time.Since(startedAt), 2*time.Second)
+}
+
+func TestParentExitWatcherTerminatesChildWhenParentExits(t *testing.T) {
+	executable, err := os.Executable()
+	require.NoError(t, err)
+
+	helper := exec.Command(executable, "-test.run=^TestParentExitWatcherHelper$") //nolint:gosec
+	helper.Env = append(os.Environ(), parentExitWatcherHelperEnv+"=1")
+
+	stdout, err := helper.StdoutPipe()
+	require.NoError(t, err)
+	require.NoError(t, helper.Start())
+
+	scanner := bufio.NewScanner(stdout)
+	require.True(t, scanner.Scan(), "helper did not print child pid")
+	childPID, err := strconv.Atoi(strings.TrimSpace(scanner.Text()))
+	require.NoError(t, err)
+
+	require.NoError(t, helper.Wait())
+	require.Eventually(t, func() bool {
+		return !processExists(childPID)
+	}, 3*time.Second, 50*time.Millisecond)
+}
+
+func TestParentExitWatcherHelper(t *testing.T) {
+	if os.Getenv(parentExitWatcherHelperEnv) != "1" {
+		t.Skip("helper only")
+	}
+
+	cmd := exec.Command("/bin/sh", "-c", "sleep 30") //nolint:gosec
+	cmd.Env = []string{"PATH=/usr/bin:/bin"}
+	proc, err := cmdutil.StartManagedProcess(cmd)
+	require.NoError(t, err)
+
+	fmt.Println(proc.PID())
+	os.Exit(0)
+}
+
+func processExists(pid int) bool {
+	err := syscall.Kill(pid, 0)
+	if err == nil {
+		return true
+	}
+	return !errors.Is(err, syscall.ESRCH)
+}