fix(tests): correct errors.Is argument order and revert unrelated rename

- Fix reversed arguments in errors.Is calls in tests
- Revert cp -> copy rename in codex_provider.go to keep PR focused

pkg/providers/codex_provider.go

@@ -91,8 +91,8 @@ func (p *CodexProvider) Chat(ctx context.Context, messages []Message, tools []To
 		if evt.Type == "response.completed" || evt.Type == "response.failed" || evt.Type == "response.incomplete" {
 			evtResp := evt.Response
 			if evtResp.ID != "" {
-				cp := evtResp
-				resp = &cp
+				copy := evtResp
+				resp = &copy
 			}
 		}
 	}

pkg/providers/error_classifier_test.go

@@ -293,7 +293,7 @@ func TestFailoverError_ErrorString(t *testing.T) {
 func TestFailoverError_Unwrap(t *testing.T) {
 	inner := errors.New("inner error")
 	fe := &FailoverError{Reason: FailoverTimeout, Wrapped: inner}
-	if !errors.Is(inner, fe.Unwrap()) {
+	if !errors.Is(fe.Unwrap(), inner) {
 		t.Error("Unwrap should return wrapped error")
 	}
 }

pkg/tools/message_test.go

@@ -126,7 +126,7 @@ func TestMessageTool_Execute_SendFailure(t *testing.T) {
 	if result.Err == nil {
 		t.Error("Expected Err to be set")
 	}
-	if !errors.Is(sendErr, result.Err) {
+	if !errors.Is(result.Err, sendErr) {
 		t.Errorf("Expected Err to be sendErr, got %v", result.Err)
 	}
 }