diff --git a/server/internal/library/imtenant/im_table_prefix_guard_test.go b/server/internal/library/imtenant/im_table_prefix_guard_test.go
new file mode 100644
index 0000000..f73cbf0
--- /dev/null
+++ b/server/internal/library/imtenant/im_table_prefix_guard_test.go
@@ -0,0 +1,56 @@
+package imtenant
+
+import (
+	"os"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestNoDirectDefaultDBModelForIMTables(t *testing.T) {
+	_, file, _, ok := runtime.Caller(0)
+	if !ok {
+		t.Fatal("runtime caller unavailable")
+	}
+	serverRoot := filepath.Clean(filepath.Join(filepath.Dir(file), "..", "..", ".."))
+	internalRoot := filepath.Join(serverRoot, "internal")
+	patterns := []*regexp.Regexp{
+		regexp.MustCompile(`g\.DB\(\)\.Model\(\s*"im_`),
+		regexp.MustCompile(`g\.DB\(\)\.Model\(\s*` + "`" + `im_`),
+		regexp.MustCompile(`g\.DB\(\)\.(Insert|InsertIgnore|Replace|Save|Update|Delete)\([^,\n]+,\s*"im_`),
+		regexp.MustCompile(`g\.DB\(\)\.(Insert|InsertIgnore|Replace|Save|Update|Delete)\([^,\n]+,\s*` + "`" + `im_`),
+	}
+
+	var violations []string
+	err := filepath.WalkDir(internalRoot, func(path string, d os.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() {
+			return nil
+		}
+		if !strings.HasSuffix(path, ".go") || strings.HasSuffix(path, "_test.go") {
+			return nil
+		}
+		content, err := os.ReadFile(path)
+		if err != nil {
+			return err
+		}
+		for _, pattern := range patterns {
+			if pattern.Match(content) {
+				rel, _ := filepath.Rel(serverRoot, path)
+				violations = append(violations, rel)
+				break
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(violations) > 0 {
+		t.Fatalf("IM public tables must not use default g.DB() model helpers because the default DB has table prefix: %s", strings.Join(violations, ", "))
+	}
+}