Install sets a default LOG_FILE in the env file on Windows (no console as a service)

internal/service/service_windows.go

@@ -152,25 +152,33 @@ func Install(configPath string, copyBin bool) error {
 		}
 	}
 
-	installDir, _ := installDirs()
-	if copyBin && !strings.EqualFold(filepath.Dir(exe), installDir) {
-		if err := os.MkdirAll(installDir, 0o755); err != nil {
-			return fmt.Errorf("create %s: %w", installDir, err)
-		}
-		installedExe := filepath.Join(installDir, "gpu-turnstile.exe")
-		if same, _ := sameFileContent(exe, installedExe); !same {
-			if err := copyFile(exe, installedExe); err != nil {
-				return fmt.Errorf("copy binary to %s: %w", installedExe, err)
-			}
-		}
-		exe = installedExe
+	installDir, dataDir := installDirs()
+	if copyBin {
 		targetCfg := filepath.Join(installDir, "gpu-turnstile.env")
-		if configPath != "" && !strings.EqualFold(configPath, targetCfg) {
-			if _, statErr := os.Stat(targetCfg); os.IsNotExist(statErr) {
-				copyFile(configPath, targetCfg) //nolint:errcheck // best effort
+		if !strings.EqualFold(filepath.Dir(exe), installDir) {
+			if err := os.MkdirAll(installDir, 0o755); err != nil {
+				return fmt.Errorf("create %s: %w", installDir, err)
+			}
+			installedExe := filepath.Join(installDir, "gpu-turnstile.exe")
+			if same, _ := sameFileContent(exe, installedExe); !same {
+				if err := copyFile(exe, installedExe); err != nil {
+					return fmt.Errorf("copy binary to %s: %w", installedExe, err)
+				}
+			}
+			exe = installedExe
+			if configPath != "" && !strings.EqualFold(configPath, targetCfg) {
+				if _, statErr := os.Stat(targetCfg); os.IsNotExist(statErr) {
+					copyFile(configPath, targetCfg) //nolint:errcheck // best effort
+				}
 			}
-			configPath = targetCfg
 		}
+		// A service has no console: without LOG_FILE the output vanishes, so
+		// the installed env file defaults to logging into ProgramData. An
+		// existing LOG_FILE setting is left alone.
+		if err := ensureLogFile(targetCfg, filepath.Join(dataDir, "gpu-turnstile.log")); err != nil {
+			return err
+		}
+		configPath = targetCfg
 	}
 	binPath := fmt.Sprintf(`"%s" -config "%s"`, exe, configPath)
 
@@ -304,6 +312,30 @@ func sameFileContent(a, b string) (bool, error) {
 	return bytes.Equal(ba, bb), nil
 }
 
+// ensureLogFile makes sure the env file at path sets LOG_FILE, creating
+// the file or appending the line as needed. An existing LOG_FILE= line
+// (even an empty one) is respected and left untouched.
+func ensureLogFile(path, logPath string) error {
+	data, err := os.ReadFile(path)
+	if err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("read %s: %w", path, err)
+	}
+	for _, line := range strings.Split(string(data), "\n") {
+		if strings.HasPrefix(strings.TrimSpace(line), "LOG_FILE=") {
+			return nil
+		}
+	}
+	s := string(data)
+	if s != "" && !strings.HasSuffix(s, "\n") {
+		s += "\n"
+	}
+	s += "LOG_FILE=" + logPath + "\n"
+	if err := os.WriteFile(path, []byte(s), 0o644); err != nil {
+		return fmt.Errorf("write %s: %w", path, err)
+	}
+	return nil
+}
+
 // copyFile copies src to dst (0755 on the new file).
 func copyFile(src, dst string) error {
 	in, err := os.Open(src)