fix: code quality, memory safety, and install improvements

Critical fixes:
- Fix Dockerfile: reorder stages so frontend assets embed into Go binary
- Fix Go version 1.25 (nonexistent) to 1.24 across Dockerfile, go.mod, CI
- Add graceful game server shutdown on SIGTERM/SIGINT
- Order startup tasks: updates complete before auto-start
- Fix TOCTOU race in UpdateSettings with atomic Update() method

Security:
- Add optional AUTH_TOKEN bearer auth middleware on API/WS routes
- Fix path traversal in DeleteMod using filepath.Rel instead of HasPrefix
- Add input validation for IPPort, ServerParameters, ScheduledUpdate

Memory safety:
- Cap RPT buffer allocation to 64KB to prevent OOM on large logs
- Cap GetLog file read to 10MB
- Fix context cancel leak in SteamCmdManager.run()
- Remove data-raced cancel field in steamcmd.go
- Atomic file writes (write-temp-then-rename) across all managers

Reliability:
- Log save errors in ProcessManager.Stop()
- Atomic file writes prevent corruption on crash

Tests:
- Add mod_manager_test.go (12 tests: ListWorkshopMods, ListLocalMods,
  BuildUsageMap, RemoveMod, dirSize)
- Add scheduler_test.go (6 tests: Start/Stop, Refresh with empty,
  invalid, valid, and replaced cron expressions)
- Add TestRestart to server_process_test.go

CI/Docs:
- Add -race flag to go test in CI and Makefile
- Add npm lint step to CI
- Add Go/npm module caching to CI
- Update README: prerequisites, AUTH_TOKEN/GIN_MODE/SERVERS_DIR docs,
  fix manual quickstart to use make build

.gitea/workflows/ci.yml

@@ -12,12 +12,17 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5
         with:
-          go-version: "1.25"
+          go-version: "1.24"
+          cache: true
+          cache-dependency-path: backend/go.sum
       - uses: actions/setup-node@v4
         with:
           node-version: "22"
+          cache: "npm"
+          cache-dependency-path: frontend/package-lock.json
       - run: cd frontend && npm ci && npm run build
       - run: mkdir -p backend/embed/dist && cp -r frontend/dist/. backend/embed/dist/
       - run: cd backend && go build ./...
-      - run: cd backend && go test ./...
+      - run: cd backend && go test -race ./...
+      - run: cd frontend && npm run lint
       - run: cd frontend && npm test

.gitea/workflows/release.yml

@@ -13,7 +13,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-go@v5
         with:
-          go-version: "1.25"
+          go-version: "1.24"
       - uses: actions/setup-node@v4
         with:
           node-version: "22"

Dockerfile

@@ -1,10 +1,3 @@
-FROM golang:1.25-bookworm AS backend
-WORKDIR /src
-COPY backend/go.mod backend/go.sum ./
-RUN go mod download
-COPY backend/ .
-RUN CGO_ENABLED=0 go build -o /server ./cmd/server/
-
 FROM node:22-alpine AS frontend
 WORKDIR /src
 COPY frontend/package.json frontend/package-lock.json ./
@@ -12,6 +5,14 @@ RUN npm ci
 COPY frontend/ .
 RUN npm run build
 
+FROM golang:1.24-bookworm AS backend
+WORKDIR /src
+COPY backend/go.mod backend/go.sum ./
+RUN go mod download
+COPY --from=frontend /src/dist /src/embed/dist
+COPY backend/ .
+RUN CGO_ENABLED=0 go build -o /server ./cmd/server/
+
 FROM debian:bookworm-slim
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \

Makefile

@@ -42,7 +42,7 @@ clean:
 	rm -rf frontend/dist backend/embed/dist bin
 
 test-backend:
-	cd backend && go test ./...
+	cd backend && go test -race ./...
 
 test-frontend:
 	cd frontend && npm test

README.md

@@ -24,18 +24,22 @@ The web UI is served on `http://localhost:8080`.
 
 ### Manual
 
-```bash
-# Backend
-cd backend
-go build -o arma3-web-server ./cmd/server
-./arma3-web-server
+**Prerequisites:**
+- [Go](https://go.dev/dl/) >= 1.24
+- [Node.js](https://nodejs.org/) >= 22 with npm
+- GNU Make (optional, for `make` targets)
 
-# Frontend (development)
-cd frontend
-npm install
-npm run dev
+```bash
+# Build for production (frontend + backend in one binary)
+make build
+./backend/arma3-web-server
+
+# Or develop with hot reload (uses test stubs, no real SteamCMD needed)
+make dev
 ```
 
+The web UI is served on `http://localhost:8080`.
+
 ## Configuration
 
 All paths are configurable via environment variables:
@@ -51,6 +55,9 @@ All paths are configurable via environment variables:
 | `SERVER_BINARY` | `arma3server_x64` | Server binary filename (overrides platform default) |
 | `SERVER_PARAMS` | `-server -world=empty ...` | Override server launch parameters |
 | `STEAMCMD_PATH` | `steamcmd` | Path to steamcmd binary |
+| `AUTH_TOKEN` | _(empty)_ | Bearer token for API/WS auth. When set, all requests must include `Authorization: Bearer <token>`. When empty, no auth required. |
+| `GIN_MODE` | `debug` | Gin framework mode. Use `release` for production (set automatically in Docker). |
+| `SERVERS_DIR` | `./serverfiles` | Docker Compose only: host directory mounted as `/servers` in the container. |
 
 ## Automation
 
@@ -66,7 +73,7 @@ Configured in the **Automation** section of the Settings UI:
 | **Auto-update mods on startup** | Downloads workshop updates for every enabled mod in the active modlist when the web service starts. |
 | **Auto-start server on startup** | Restarts the game server if it was running when the web service last stopped. Useful for recovery after host backup cycles or container restarts. |
 
-All startup tasks run asynchronously — the web UI is available immediately.
+All startup tasks run asynchronously — the web UI is available immediately. Server and mod updates run in parallel; auto-start waits for both to complete before launching the game server.
 
 ### Scheduled updates
 

backend/cmd/server/main.go

@@ -10,6 +10,7 @@ import (
 	"os/signal"
 	"path/filepath"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -91,8 +92,12 @@ func main() {
 	if err != nil {
 		log.Printf("startup: load settings: %v", err)
 	} else {
+		var updatesWg sync.WaitGroup
+
 		if s.AutoUpdateOnStartup && s.SteamUser != "" {
+			updatesWg.Add(1)
 			go func() {
+				defer updatesWg.Done()
 				log.Print("startup: auto-updating gameserver")
 				if err := steamcmd.UpdateGame(s.SteamBranch, s.SteamUser); err != nil {
 					log.Printf("startup: auto-update game failed: %v", err)
@@ -101,7 +106,9 @@ func main() {
 		}
 
 		if s.AutoUpdateModsOnStartup && s.ActiveModlist != "" {
+			updatesWg.Add(1)
 			go func() {
+				defer updatesWg.Done()
 				log.Print("startup: auto-updating mods")
 				ml, err := modlistMgr.Get(s.ActiveModlist)
 				if err != nil {
@@ -124,6 +131,7 @@ func main() {
 
 		if s.AutoStartOnStartup && s.WasRunning {
 			go func() {
+				updatesWg.Wait()
 				log.Print("startup: auto-restarting server (was running before)")
 				if err := process.Start(); err != nil {
 					log.Printf("startup: auto-start failed: %v", err)
@@ -152,6 +160,13 @@ func main() {
 	log.Print("shutting down server...")
 	scheduler.Stop()
 
+	if process.IsRunning() {
+		log.Print("stopping game server...")
+		if err := process.Stop(); err != nil {
+			log.Printf("stop game server: %v", err)
+		}
+	}
+
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 	if err := srv.Shutdown(ctx); err != nil {

backend/internal/api/logs.go

@@ -195,7 +195,13 @@ func (h *Handler) StreamRPTLogs(c *gin.Context) {
 			if _, err := f.Seek(currentOffset, io.SeekStart); err != nil {
 				return nil
 			}
-			buf := make([]byte, fi.Size()-currentOffset)
+			remaining := fi.Size() - currentOffset
+			const maxBuf = 64 * 1024
+			bufSize := remaining
+			if bufSize > maxBuf {
+				bufSize = maxBuf
+			}
+			buf := make([]byte, bufSize)
 			n, _ := io.ReadFull(f, buf)
 
 			currentOffset += int64(n)
@@ -260,6 +266,16 @@ func (h *Handler) GetLog(c *gin.Context) {
 		}
 	}
 
+	fi, err := os.Stat(path)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	const maxLogSize = 10 * 1024 * 1024
+	if fi.Size() > maxLogSize {
+		c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "log file too large, use live streaming"})
+		return
+	}
 	data, err := os.ReadFile(path)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})

backend/internal/api/mods.go

@@ -49,6 +49,14 @@ func (h *Handler) ListMods(c *gin.Context) {
 	c.JSON(http.StatusOK, all)
 }
 
+func isUnderDir(path, dir string) bool {
+	rel, err := filepath.Rel(dir, path)
+	if err != nil {
+		return false
+	}
+	return rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator))
+}
+
 func (h *Handler) DeleteMod(c *gin.Context) {
 	var input deleteModInput
 	if err := c.ShouldBindJSON(&input); err != nil {
@@ -62,7 +70,7 @@ func (h *Handler) DeleteMod(c *gin.Context) {
 		return
 	}
 
-	if !strings.HasPrefix(absPath, h.serverfileDir) && !strings.HasPrefix(absPath, h.modsDir) {
+	if !isUnderDir(absPath, h.serverfileDir) && !isUnderDir(absPath, h.modsDir) {
 		c.JSON(http.StatusForbidden, gin.H{"error": "path outside allowed directories"})
 		return
 	}

backend/internal/api/router.go

@@ -1,6 +1,10 @@
 package api
 
 import (
+	"net/http"
+	"os"
+	"strings"
+
 	"arma3-web-server/internal/services"
 
 	"github.com/gin-gonic/gin"
@@ -20,6 +24,7 @@ type Handler struct {
 	cfgDir         string
 	profilesDir    string
 	frontendServed bool
+	authToken      string
 }
 
 func New(
@@ -47,11 +52,44 @@ func New(
 		cfgDir:         cfgDir,
 		profilesDir:    profilesDir,
 		frontendServed: frontendServed,
+		authToken:      os.Getenv("AUTH_TOKEN"),
 	}
 }
 
+func (h *Handler) authMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		if h.authToken == "" {
+			c.Next()
+			return
+		}
+		auth := c.GetHeader("Authorization")
+		if !strings.HasPrefix(auth, "Bearer ") {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "missing or invalid authorization header"})
+			return
+		}
+		token := strings.TrimPrefix(auth, "Bearer ")
+		if !secureCompare(token, h.authToken) {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "invalid token"})
+			return
+		}
+		c.Next()
+	}
+}
+
+func secureCompare(a, b string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := 0; i < len(a); i++ {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
 func (h *Handler) SetupRoutes(r *gin.Engine) {
-	api := r.Group("/api")
+	api := r.Group("/api", h.authMiddleware())
 	{
 		api.GET("/server/settings", h.GetSettings)
 		api.PUT("/server/settings", h.UpdateSettings)
@@ -93,7 +131,8 @@ func (h *Handler) SetupRoutes(r *gin.Engine) {
 		api.POST("/mods/cleanup", h.CleanupMods)
 	}
 
-	r.GET("/ws/server/logs", h.StreamLogs)
-	r.GET("/ws/steamcmd/logs", h.StreamSteamCMDLogs)
-	r.GET("/ws/server/rpt", h.StreamRPTLogs)
+	ws := r.Group("/ws", h.authMiddleware())
+	ws.GET("/server/logs", h.StreamLogs)
+	ws.GET("/steamcmd/logs", h.StreamSteamCMDLogs)
+	ws.GET("/server/rpt", h.StreamRPTLogs)
 }

backend/internal/api/settings.go

@@ -1,9 +1,15 @@
 package api
 
 import (
+	"fmt"
+	"net"
 	"net/http"
+	"strings"
+
+	"arma3-web-server/internal/models"
 
 	"github.com/gin-gonic/gin"
+	"github.com/robfig/cron/v3"
 )
 
 type updateSettingsInput struct {
@@ -39,12 +45,33 @@ func (h *Handler) UpdateSettings(c *gin.Context) {
 		return
 	}
 
-	s, err := h.settings.Load()
-	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+	if input.IPPort != nil && *input.IPPort != "" {
+		if _, _, err := net.SplitHostPort(*input.IPPort); err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": fmt.Sprintf("invalid ip_port: must be host:port format: %v", err)})
 			return
 		}
+	}
+	if input.ServerParameters != nil && len(*input.ServerParameters) > 8192 {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "server_parameters too long (max 8192)"})
+		return
+	}
+	if input.ScheduledUpdate != nil && *input.ScheduledUpdate != "" {
+		parser := cron.NewParser(cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow)
+		if _, err := parser.Parse(*input.ScheduledUpdate); err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": fmt.Sprintf("invalid cron expression: %v", err)})
+			return
+		}
+	}
+	if input.ServerParameters != nil {
+		for _, forbidden := range []string{"--dry-run", "--rm", "--privileged"} {
+			if strings.Contains(*input.ServerParameters, forbidden) {
+				c.JSON(http.StatusBadRequest, gin.H{"error": fmt.Sprintf("server_parameters contains forbidden flag: %s", forbidden)})
+				return
+			}
+		}
+	}
 
+	s, err := h.settings.Update(func(s *models.ServerSettings) {
 		if input.IPPort != nil {
 			s.IPPort = *input.IPPort
 		}
@@ -87,14 +114,14 @@ func (h *Handler) UpdateSettings(c *gin.Context) {
 		if input.ScheduledUpdate != nil {
 			s.ScheduledUpdate = *input.ScheduledUpdate
 		}
-
-	if err := h.process.WriteUserconfigFiles(s); err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": "write userconfig: " + err.Error()})
+	})
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
 	}
 
-	if err := h.settings.Save(s); err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+	if err := h.process.WriteUserconfigFiles(s); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "write userconfig: " + err.Error()})
 		return
 	}
 

backend/internal/services/config_manager.go

@@ -59,11 +59,11 @@ func (cm *ConfigManager) Create(name, content string) error {
 	if _, err := os.Stat(path); err == nil {
 		return fmt.Errorf("config already exists")
 	}
-	return os.WriteFile(path, []byte(content), 0644)
+	return writeFileAtomic(path, []byte(content))
 }
 
 func (cm *ConfigManager) Update(name, content string) error {
-	return os.WriteFile(cm.path(name), []byte(content), 0644)
+	return writeFileAtomic(cm.path(name), []byte(content))
 }
 
 func (cm *ConfigManager) Delete(name string) error {

backend/internal/services/mod_manager_test.go

@@ -0,0 +1,209 @@
+package services
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"arma3-web-server/internal/models"
+)
+
+func TestListWorkshopMods_Empty(t *testing.T) {
+	dir := t.TempDir()
+	mods := ListWorkshopMods(dir)
+	if len(mods) != 0 {
+		t.Fatalf("expected 0 mods, got %d", len(mods))
+	}
+}
+
+func TestListWorkshopMods_WithMods(t *testing.T) {
+	dir := t.TempDir()
+	workshopDir := filepath.Join(dir, "steamapps", "workshop", "content", "107410")
+	if err := os.MkdirAll(filepath.Join(workshopDir, "123456"), 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.MkdirAll(filepath.Join(workshopDir, "789012"), 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	mods := ListWorkshopMods(dir)
+	if len(mods) != 2 {
+		t.Fatalf("expected 2 mods, got %d", len(mods))
+	}
+
+	ids := map[string]bool{}
+	for _, m := range mods {
+		ids[m.ID] = true
+		if m.Source != "workshop" {
+			t.Errorf("expected source 'workshop', got %q", m.Source)
+		}
+	}
+	if !ids["123456"] || !ids["789012"] {
+		t.Errorf("expected both mod IDs, got %v", ids)
+	}
+}
+
+func TestListWorkshopMods_SkipsFiles(t *testing.T) {
+	dir := t.TempDir()
+	workshopDir := filepath.Join(dir, "steamapps", "workshop", "content", "107410")
+	if err := os.MkdirAll(workshopDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(workshopDir, "notadir.txt"), []byte("hi"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.MkdirAll(filepath.Join(workshopDir, "111111"), 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	mods := ListWorkshopMods(dir)
+	if len(mods) != 1 {
+		t.Fatalf("expected 1 mod, got %d", len(mods))
+	}
+	if mods[0].ID != "111111" {
+		t.Errorf("expected ID '111111', got %q", mods[0].ID)
+	}
+}
+
+func TestListLocalMods_Empty(t *testing.T) {
+	dir := t.TempDir()
+	mods := ListLocalMods(dir)
+	if len(mods) != 0 {
+		t.Fatalf("expected 0 mods, got %d", len(mods))
+	}
+}
+
+func TestListLocalMods_WithMods(t *testing.T) {
+	dir := t.TempDir()
+	if err := os.MkdirAll(filepath.Join(dir, "@ACE3"), 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.MkdirAll(filepath.Join(dir, "@TFAR"), 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	mods := ListLocalMods(dir)
+	if len(mods) != 2 {
+		t.Fatalf("expected 2 mods, got %d", len(mods))
+	}
+
+	for _, m := range mods {
+		if m.Source != "local" {
+			t.Errorf("expected source 'local', got %q", m.Source)
+		}
+		if len(m.Name) > 0 && m.Name[0] != '@' {
+			t.Errorf("expected name to start with '@', got %q", m.Name)
+		}
+	}
+}
+
+func TestListLocalMods_SkipsFiles(t *testing.T) {
+	dir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(dir, "readme.txt"), []byte("hi"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.MkdirAll(filepath.Join(dir, "@Mod"), 0755); err != nil {
+		t.Fatal(err)
+	}
+
+	mods := ListLocalMods(dir)
+	if len(mods) != 1 {
+		t.Fatalf("expected 1 mod, got %d", len(mods))
+	}
+}
+
+func TestBuildUsageMap(t *testing.T) {
+	dataDir := t.TempDir()
+	mm := NewModlistManager(dataDir)
+
+	ml, err := mm.Create("Test List")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ml, err = mm.Update(ml.ID, ml.Name, []models.ModEntry{
+		{ID: "111111", Name: "ACE3", Enabled: true},
+		{ID: "222222", Name: "", Enabled: true},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = ml
+
+	usedWorkshop, usedLocal := BuildUsageMap(mm)
+
+	if lists, ok := usedWorkshop["111111"]; !ok || len(lists) == 0 {
+		t.Errorf("expected workshop mod 111111 to be in use")
+	}
+	if _, ok := usedWorkshop["222222"]; !ok {
+		t.Errorf("expected workshop mod 222222 to be in use")
+	}
+	if _, ok := usedLocal["ACE3"]; !ok {
+		t.Errorf("expected local mod ACE3 to be in use")
+	}
+	if _, ok := usedLocal["@ACE3"]; !ok {
+		t.Errorf("expected local mod @ACE3 to be in use")
+	}
+}
+
+func TestBuildUsageMap_Empty(t *testing.T) {
+	dataDir := t.TempDir()
+	mm := NewModlistManager(dataDir)
+
+	usedWorkshop, usedLocal := BuildUsageMap(mm)
+	if len(usedWorkshop) != 0 || len(usedLocal) != 0 {
+		t.Errorf("expected empty maps, got workshop=%v local=%v", usedWorkshop, usedLocal)
+	}
+}
+
+func TestRemoveMod(t *testing.T) {
+	dir := t.TempDir()
+	modDir := filepath.Join(dir, "@TestMod")
+	if err := os.MkdirAll(modDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(modDir, "config.cpp"), []byte("x"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := RemoveMod(modDir); err != nil {
+		t.Fatalf("RemoveMod failed: %v", err)
+	}
+	if _, err := os.Stat(modDir); !os.IsNotExist(err) {
+		t.Errorf("expected directory to be removed")
+	}
+}
+
+func TestRemoveMod_Nonexistent(t *testing.T) {
+	err := RemoveMod("/nonexistent/path/that/does/not/exist")
+	if err != nil {
+		t.Errorf("RemoveMod on nonexistent path should not error, got: %v", err)
+	}
+}
+
+func TestDirSize(t *testing.T) {
+	dir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(dir, "a.txt"), []byte("hello"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	sub := filepath.Join(dir, "sub")
+	if err := os.MkdirAll(sub, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(sub, "b.txt"), []byte("world!"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	size := dirSize(dir)
+	if size != 11 {
+		t.Errorf("expected size 11, got %d", size)
+	}
+}
+
+func TestDirSize_Empty(t *testing.T) {
+	dir := t.TempDir()
+	size := dirSize(dir)
+	if size != 0 {
+		t.Errorf("expected size 0, got %d", size)
+	}
+}

backend/internal/services/modlist_manager.go

@@ -103,7 +103,7 @@ func (mm *ModlistManager) Create(name string) (*models.Modlist, error) {
 	if err := os.MkdirAll(mm.dir, 0755); err != nil {
 		return nil, err
 	}
-	if err := os.WriteFile(mm.path(m.ID), data, 0644); err != nil {
+	if err := writeFileAtomic(mm.path(m.ID), data); err != nil {
 		return nil, err
 	}
 	return m, nil
@@ -126,7 +126,7 @@ func (mm *ModlistManager) Update(id, name string, mods []models.ModEntry) (*mode
 	if err != nil {
 		return nil, err
 	}
-	if err := os.WriteFile(mm.path(id), data, 0644); err != nil {
+	if err := writeFileAtomic(mm.path(id), data); err != nil {
 		return nil, err
 	}
 	return m, nil
@@ -160,7 +160,7 @@ func (mm *ModlistManager) Duplicate(id, newName string) (*models.Modlist, error)
 	if err != nil {
 		return nil, err
 	}
-	if err := os.WriteFile(mm.path(dup.ID), data, 0644); err != nil {
+	if err := writeFileAtomic(mm.path(dup.ID), data); err != nil {
 		return nil, err
 	}
 	return dup, nil

backend/internal/services/scheduler_test.go

@@ -0,0 +1,136 @@
+package services
+
+import (
+	"testing"
+	"time"
+
+	"arma3-web-server/internal/models"
+)
+
+func TestNewScheduler(t *testing.T) {
+	dataDir := t.TempDir()
+	settings := NewSettingsManager(dataDir)
+	modlists := NewModlistManager(dataDir)
+	streamer := NewLogStreamer()
+	steamcmd := NewSteamCmdManager(t.TempDir(), streamer)
+
+	s := NewScheduler(settings, modlists, steamcmd)
+	if s == nil {
+		t.Fatal("expected non-nil scheduler")
+	}
+	if s.cron == nil {
+		t.Fatal("expected non-nil cron")
+	}
+}
+
+func TestScheduler_StartStop(t *testing.T) {
+	dataDir := t.TempDir()
+	settings := NewSettingsManager(dataDir)
+	modlists := NewModlistManager(dataDir)
+	streamer := NewLogStreamer()
+	steamcmd := NewSteamCmdManager(t.TempDir(), streamer)
+
+	s := NewScheduler(settings, modlists, steamcmd)
+	s.Start()
+	time.Sleep(50 * time.Millisecond)
+	s.Stop()
+}
+
+func TestScheduler_Refresh_Empty(t *testing.T) {
+	dataDir := t.TempDir()
+	settings := NewSettingsManager(dataDir)
+	modlists := NewModlistManager(dataDir)
+	streamer := NewLogStreamer()
+	steamcmd := NewSteamCmdManager(t.TempDir(), streamer)
+
+	s := NewScheduler(settings, modlists, steamcmd)
+	s.Start()
+	defer s.Stop()
+
+	s.Refresh()
+	if s.entryID != 0 {
+		t.Errorf("expected entryID 0 with empty settings, got %d", s.entryID)
+	}
+}
+
+func TestScheduler_Refresh_InvalidCron(t *testing.T) {
+	dataDir := t.TempDir()
+	settings := NewSettingsManager(dataDir)
+	modlists := NewModlistManager(dataDir)
+	streamer := NewLogStreamer()
+	steamcmd := NewSteamCmdManager(t.TempDir(), streamer)
+
+	_, err := settings.Update(func(s *models.ServerSettings) {
+		s.ScheduledUpdate = "not-a-cron"
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	sched := NewScheduler(settings, modlists, steamcmd)
+	sched.Start()
+	defer sched.Stop()
+
+	sched.Refresh()
+	if sched.entryID != 0 {
+		t.Errorf("expected entryID 0 with invalid cron, got %d", sched.entryID)
+	}
+}
+
+func TestScheduler_Refresh_ValidCron(t *testing.T) {
+	dataDir := t.TempDir()
+	settings := NewSettingsManager(dataDir)
+	modlists := NewModlistManager(dataDir)
+	streamer := NewLogStreamer()
+	steamcmd := NewSteamCmdManager(t.TempDir(), streamer)
+
+	_, err := settings.Update(func(s *models.ServerSettings) {
+		s.ScheduledUpdate = "0 4 * * *"
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	sched := NewScheduler(settings, modlists, steamcmd)
+	sched.Start()
+	defer sched.Stop()
+
+	sched.Refresh()
+	if sched.entryID == 0 {
+		t.Errorf("expected non-zero entryID with valid cron")
+	}
+}
+
+func TestScheduler_Refresh_Replace(t *testing.T) {
+	dataDir := t.TempDir()
+	settings := NewSettingsManager(dataDir)
+	modlists := NewModlistManager(dataDir)
+	streamer := NewLogStreamer()
+	steamcmd := NewSteamCmdManager(t.TempDir(), streamer)
+
+	sched := NewScheduler(settings, modlists, steamcmd)
+	sched.Start()
+	defer sched.Stop()
+
+	_, err := settings.Update(func(s *models.ServerSettings) {
+		s.ScheduledUpdate = "0 4 * * *"
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	sched.Refresh()
+	id1 := sched.entryID
+
+	_, err = settings.Update(func(s *models.ServerSettings) {
+		s.ScheduledUpdate = "0 5 * * *"
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	sched.Refresh()
+	id2 := sched.entryID
+
+	if id1 == id2 {
+		t.Errorf("expected different entryIDs after refresh, both got %d", id1)
+	}
+}

backend/internal/services/server_process.go

@@ -3,6 +3,7 @@ package services
 import (
 	"context"
 	"fmt"
+	"log"
 	"net"
 	"os"
 	"os/exec"
@@ -184,7 +185,9 @@ func (pm *ProcessManager) Stop() error {
 	s, err := pm.settings.Load()
 	if err == nil {
 		s.WasRunning = false
-		pm.settings.Save(s)
+		if err := pm.settings.Save(s); err != nil {
+			log.Printf("stop: save was_running: %v", err)
+		}
 	}
 
 	return nil
@@ -307,7 +310,7 @@ func (pm *ProcessManager) WriteUserconfigFiles(s *models.ServerSettings) error {
 	}
 	for name, content := range files {
 		path := filepath.Join(userconfigDir, name)
-		if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		if err := writeFileAtomic(path, []byte(content)); err != nil {
 			return fmt.Errorf("write %s: %w", name, err)
 		}
 	}

backend/internal/services/server_process_test.go

@@ -983,3 +983,29 @@ func TestStart_StubWritesRPTLog(t *testing.T) {
 	pm.Stop()
 	time.Sleep(100 * time.Millisecond)
 }
+
+func TestRestart(t *testing.T) {
+	pm, _ := setupStubPM(t, "-t 10")
+
+	if err := pm.Start(); err != nil {
+		t.Fatalf("Start() error = %v", err)
+	}
+	if !pm.IsRunning() {
+		t.Fatal("IsRunning() should be true after Start()")
+	}
+
+	if err := pm.Restart(); err != nil {
+		t.Fatalf("Restart() error = %v", err)
+	}
+	if !pm.IsRunning() {
+		t.Fatal("IsRunning() should be true after Restart()")
+	}
+
+	if err := pm.Stop(); err != nil {
+		t.Fatalf("Stop() error = %v", err)
+	}
+	time.Sleep(100 * time.Millisecond)
+	if pm.IsRunning() {
+		t.Fatal("IsRunning() should be false after Stop()")
+	}
+}

backend/internal/services/settings.go

@@ -10,6 +10,29 @@ import (
 	"arma3-web-server/internal/models"
 )
 
+func writeFileAtomic(path string, data []byte) error {
+	dir := filepath.Dir(path)
+	tmp, err := os.CreateTemp(dir, ".tmp-*")
+	if err != nil {
+		return err
+	}
+	tmpPath := tmp.Name()
+	if _, err := tmp.Write(data); err != nil {
+		tmp.Close()
+		os.Remove(tmpPath)
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		os.Remove(tmpPath)
+		return err
+	}
+	if err := os.Rename(tmpPath, path); err != nil {
+		os.Remove(tmpPath)
+		return err
+	}
+	return nil
+}
+
 type SettingsManager struct {
 	path string
 	mu   sync.Mutex
@@ -49,7 +72,45 @@ func (sm *SettingsManager) Save(s *models.ServerSettings) error {
 	if err != nil {
 		return err
 	}
-	return os.WriteFile(sm.path, data, 0644)
+	return writeFileAtomic(sm.path, data)
+}
+
+func (sm *SettingsManager) Update(fn func(*models.ServerSettings)) (*models.ServerSettings, error) {
+	sm.mu.Lock()
+	defer sm.mu.Unlock()
+
+	data, err := os.ReadFile(sm.path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			s := sm.defaults()
+			fn(s)
+			s.UpdatedAt = time.Now().UTC()
+			out, err := json.MarshalIndent(s, "", "  ")
+			if err != nil {
+				return nil, err
+			}
+			if err := writeFileAtomic(sm.path, out); err != nil {
+				return nil, err
+			}
+			return s, nil
+		}
+		return nil, err
+	}
+
+	var s models.ServerSettings
+	if err := json.Unmarshal(data, &s); err != nil {
+		return nil, err
+	}
+	fn(&s)
+	s.UpdatedAt = time.Now().UTC()
+	out, err := json.MarshalIndent(s, "", "  ")
+	if err != nil {
+		return nil, err
+	}
+	if err := writeFileAtomic(sm.path, out); err != nil {
+		return nil, err
+	}
+	return &s, nil
 }
 
 func (sm *SettingsManager) defaults() *models.ServerSettings {

backend/internal/services/steamcmd.go

@@ -25,7 +25,6 @@ type SteamCmdManager struct {
 	serverfileDir string
 	streamer      *LogStreamer
 	running       atomic.Bool
-	cancel        context.CancelFunc
 }
 
 func NewSteamCmdManager(serverfileDir string, streamer *LogStreamer) *SteamCmdManager {
@@ -115,15 +114,13 @@ func (s *SteamCmdManager) run(label string, args []string) error {
 		return fmt.Errorf("start steamcmd: %w", err)
 	}
 
-	s.cancel = cancel
-
 	go s.streamer.Stream(ctx, "steamcmd", stdout, "")
 	go s.streamer.Stream(ctx, "steamcmd", stderr, "")
 
 	go func() {
 		err := cmd.Wait()
+		cancel()
 		s.running.Store(false)
-		s.cancel = nil
 		if err == nil {
 			s.streamer.Broadcast("steamcmd", "[STEAMCMD] SUCCESS: "+label+" finished")
 		} else {