Enhance environment variable documentation and configuration

Co-authored-by: Cursor <cursoragent@cursor.com>

cmd/scratchbox/main_test.go

@@ -135,6 +135,7 @@ func TestMainProcessEnvSuccess(t *testing.T) {
 	cmd.Env = append(os.Environ(),
 		"GO_WANT_MAIN_HELPER=1",
 		"MAIN_HELPER_MODE=env-success",
+		// These are from the canonical envSuffixes list (internal/config/config.go)
 		"SCRATCHBOX_SERVER_LISTEN_ADDR=127.0.0.1:0",
 		"SCRATCHBOX_STORAGE_DATA_DIR="+filepath.Join(tmp, "data"),
 		"SCRATCHBOX_SECURITY_ALLOWED_IPS=",

cmd/scratchbox/server.go

@@ -34,7 +34,7 @@ func newServerCmd() *cobra.Command {
 		},
 	}
 	cmd.Flags().StringVarP(&configPath, "config", "c", "", "path to config file")
-	cmd.Flags().BoolVar(&useEnv, "env", false, "load config from SCRATCHBOX_* environment variables")
+	cmd.Flags().BoolVar(&useEnv, "env", false, "load config from SCRATCHBOX_* environment variables (see envSuffixes in internal/config/config.go)")
 	cmd.MarkFlagsMutuallyExclusive("config", "env")
 	return cmd
 }
@@ -134,6 +134,8 @@ func run(configPath string, useEnv bool) error {
 }
 
 func printEnvStartup() int {
+	// All SCRATCHBOX_* variables are defined by envSuffixes (single source of truth)
+	// in internal/config/config.go. See the comment there for update rules.
 	entries := make([]string, 0)
 	for _, item := range os.Environ() {
 		if strings.HasPrefix(item, "SCRATCHBOX_") {