fix(mtproto): synchronize child-process lifecycle (#6141)

* fix(mtproto): synchronize child-process state

Use lifecycle snapshots around the mtg command, completion signal, and exit error so Wait cannot race status and shutdown reads.

* test(mtproto): cover concurrent process exit

* test(mtproto): cover lifecycle field synchronization

---------

Co-authored-by: PathGao <gaoyanbo@gaoyanbodeMacBook-Air.local>

internal/mtproto/process_race_test.go

@@ -0,0 +1,106 @@
+package mtproto
+
+import (
+	"errors"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestProcessLifecycleFieldsRaceSafe(t *testing.T) {
+	proc := newProcess("", "test")
+	stop := make(chan struct{})
+	var workers sync.WaitGroup
+	defer func() {
+		close(stop)
+		workers.Wait()
+	}()
+
+	workers.Go(func() {
+		for {
+			select {
+			case <-stop:
+				return
+			default:
+			}
+			proc.mu.Lock()
+			proc.cmd = &exec.Cmd{}
+			proc.done = make(chan struct{})
+			proc.mu.Unlock()
+			proc.setExitErr(errors.New("exit"))
+		}
+	})
+	for range 4 {
+		workers.Go(func() {
+			for {
+				select {
+				case <-stop:
+					return
+				default:
+				}
+				_ = proc.IsRunning()
+				_ = proc.GetResult()
+			}
+		})
+	}
+
+	time.Sleep(50 * time.Millisecond)
+}
+
+func TestProcessStatusDuringExit(t *testing.T) {
+	pidFile := installFakeMtg(t)
+	exitFile := filepath.Join(t.TempDir(), "exit")
+	t.Setenv("MTG_FAKE_EXIT_FILE", exitFile)
+	configPath := filepath.Join(t.TempDir(), "mtg.toml")
+	if err := os.WriteFile(configPath, nil, 0o600); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
+	proc := newProcess(configPath, "test")
+	if err := proc.Start(); err != nil {
+		t.Fatalf("start process: %v", err)
+	}
+	t.Cleanup(func() {
+		_ = proc.Stop()
+	})
+	waitSpawnCount(t, pidFile, 1)
+
+	stopReads := make(chan struct{})
+	var readers sync.WaitGroup
+	defer func() {
+		close(stopReads)
+		readers.Wait()
+	}()
+	for range 4 {
+		readers.Go(func() {
+			for {
+				select {
+				case <-stopReads:
+					return
+				default:
+					_ = proc.IsRunning()
+					_ = proc.GetResult()
+				}
+			}
+		})
+	}
+
+	proc.mu.RLock()
+	done := proc.done
+	proc.mu.RUnlock()
+	if err := os.WriteFile(exitFile, nil, 0o600); err != nil {
+		t.Fatalf("trigger exit: %v", err)
+	}
+	if err := waitForExit(done, time.Second); err != nil {
+		t.Fatalf("wait for process exit: %v", err)
+	}
+	if proc.IsRunning() {
+		t.Fatal("process must not be running after exit")
+	}
+	if got := proc.GetResult(); !strings.Contains(got, "exit status 1") {
+		t.Fatalf("GetResult after an unexpected exit = %q, want exit status", got)
+	}
+}