diff --git a/zddc/internal/handler/fileapi_test.go b/zddc/internal/handler/fileapi_test.go
index 92a6140..7e333b3 100644
--- a/zddc/internal/handler/fileapi_test.go
+++ b/zddc/internal/handler/fileapi_test.go
@@ -918,3 +918,34 @@ func TestFileAPI_MoveRenamesHistoryDir(t *testing.T) {
 		t.Errorf("history should NOT follow a cross-dir move; err=%v", err)
 	}
 }
+
+// TestFileAPI_PreservesCase — mkdir + PUT must keep the basename's case
+// verbatim (tracking numbers are uppercase; the server must not normalize).
+func TestFileAPI_PreservesCase(t *testing.T) {
+	// working/<party>/… is the realistic create surface; the harness
+	// auto-registers Acme so the party gate passes. Subfolder + file names
+	// under it are arbitrary — isolates the basename-case question.
+	_, do, root := fileAPITestSetup(t, []string{"Proj/working/Acme"}, nil)
+	base := filepath.Join(root, "Proj", "working", "Acme")
+
+	rec := do(http.MethodPost, "/Proj/working/Acme/MixedCaseDir", "alice@example.com", nil, map[string]string{"X-ZDDC-Op": "mkdir"})
+	if rec.Code != http.StatusCreated && rec.Code != http.StatusOK {
+		t.Fatalf("mkdir: %d %s", rec.Code, rec.Body.String())
+	}
+	rec = do(http.MethodPut, "/Proj/working/Acme/UPPER-Name.MD", "alice@example.com", []byte("# hi\n"), map[string]string{"Content-Type": "text/markdown"})
+	if rec.Code != http.StatusCreated && rec.Code != http.StatusOK {
+		t.Fatalf("put: %d %s", rec.Code, rec.Body.String())
+	}
+	ents, _ := os.ReadDir(base)
+	var names []string
+	for _, e := range ents {
+		names = append(names, e.Name())
+	}
+	t.Logf("on-disk under working/Acme: %v", names)
+	if _, err := os.Stat(filepath.Join(base, "MixedCaseDir")); err != nil {
+		t.Errorf("mkdir case NOT preserved (%v)", names)
+	}
+	if _, err := os.Stat(filepath.Join(base, "UPPER-Name.MD")); err != nil {
+		t.Errorf("PUT case NOT preserved (%v)", names)
+	}
+}