fix(updater): build in temp directory, replace old launcher binary, and cleanup temp

internal/git-service/launcher.go

@@ -10,6 +10,8 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"os/exec"
+	"path/filepath"
 	"regexp"
 	"strings"
 	"time"
@@ -87,7 +89,72 @@ func (g *GitService) UpdateLauncherProgress(version string) (bool, string) {
 		}
 	}
 
-	return false, "could not locate valid launcher update package"
+	// Mode 3: Build from source inside a temporary workspace, replace binary, and delete temp
+	return g.BuildAndUpdateFromSource(constant.LauncherBranch)
+}
+
+func (g *GitService) BuildAndUpdateFromSource(branch string) (bool, string) {
+	if branch == "" {
+		branch = constant.LauncherBranch
+	}
+
+	gitExe, err := ensureGit()
+	if err != nil {
+		return false, fmt.Sprintf("git is required for source update: %v", err)
+	}
+
+	// 1. Create clean temporary directory
+	tempDir, err := os.MkdirTemp("", "g-launcher-build-*")
+	if err != nil {
+		return false, fmt.Sprintf("create temp build directory: %v", err)
+	}
+	defer os.RemoveAll(tempDir) // Guarantee temporary directory is completely deleted
+
+	// 2. Clone repository into temp directory
+	cloneCmd := exec.Command(gitExe, "clone", "--depth", "1", "--branch", branch, constant.LauncherRepoURL, tempDir)
+	cloneCmd.Env = append(os.Environ(), "GIT_TERMINAL_PROMPT=0")
+	if out, err := cloneCmd.CombinedOutput(); err != nil {
+		return false, fmt.Sprintf("clone repository to temp: %v (%s)", err, strings.TrimSpace(string(out)))
+	}
+
+	// 3. Build frontend inside temp
+	frontendDir := filepath.Join(tempDir, "frontend")
+	npmInstall := exec.Command("npm", "install", "--no-audit", "--no-fund")
+	npmInstall.Dir = frontendDir
+	if out, err := npmInstall.CombinedOutput(); err != nil {
+		return false, fmt.Sprintf("npm install in temp: %v (%s)", err, strings.TrimSpace(string(out)))
+	}
+
+	npmBuild := exec.Command("npm", "run", "build")
+	npmBuild.Dir = frontendDir
+	if out, err := npmBuild.CombinedOutput(); err != nil {
+		return false, fmt.Sprintf("npm run build in temp: %v (%s)", err, strings.TrimSpace(string(out)))
+	}
+
+	// 4. Build Go binary inside temp
+	builtExePath := filepath.Join(tempDir, "bin", "G-Launcher.exe")
+	if err := os.MkdirAll(filepath.Dir(builtExePath), 0755); err != nil {
+		return false, fmt.Sprintf("create temp bin directory: %v", err)
+	}
+
+	goBuild := exec.Command("go", "build", "-tags", "production", "-trimpath", "-buildvcs=false", "-ldflags=-w -s -H windowsgui", "-o", builtExePath, ".")
+	goBuild.Dir = tempDir
+	if out, err := goBuild.CombinedOutput(); err != nil {
+		return false, fmt.Sprintf("go build in temp: %v (%s)", err, strings.TrimSpace(string(out)))
+	}
+
+	// 5. Replace current running binary with newly built binary
+	builtFile, err := os.Open(builtExePath)
+	if err != nil {
+		return false, fmt.Sprintf("open built launcher in temp: %v", err)
+	}
+	defer builtFile.Close()
+
+	if err := selfupdate.Apply(builtFile, selfupdate.Options{}); err != nil {
+		return false, fmt.Sprintf("apply launcher update: %v", err)
+	}
+
+	return true, ""
 }
 
 func (g *GitService) applyManifestUpdate(manifest launcherManifest) (bool, string) {