fix(handler): preserve origin on form submissions

Use the same-origin referrer policy to prevent Chrome from sending a null Origin header on POST requests.

app/internal/handler/handler.go

@@ -131,7 +131,7 @@ func (h *Handler) serverError(w http.ResponseWriter, r *http.Request, err error)
 func (h *Handler) security(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Security-Policy", "default-src 'self'; style-src 'self'; form-action 'self'; frame-ancestors 'none'; base-uri 'self'")
-		w.Header().Set("Referrer-Policy", "no-referrer")
+		w.Header().Set("Referrer-Policy", "same-origin")
 		w.Header().Set("X-Content-Type-Options", "nosniff")
 		w.Header().Set("X-Frame-Options", "DENY")
 		next.ServeHTTP(w, r)

app/internal/handler/handler_test.go

@@ -56,6 +56,9 @@ func TestListRendersEscapedTodos(t *testing.T) {
 	if strings.Contains(recorder.Body.String(), "<script>") || !strings.Contains(recorder.Body.String(), "&lt;script&gt;") {
 		t.Fatalf("title was not escaped: %s", recorder.Body.String())
 	}
+	if got := recorder.Header().Get("Referrer-Policy"); got != "same-origin" {
+		t.Fatalf("Referrer-Policy = %q, want %q", got, "same-origin")
+	}
 }
 
 func TestCreateValidatesAndTrimsTitle(t *testing.T) {