fix: suppress remaining errcheck failures in test and oauth code

- internal/ghl/oauth.go:186: defer func(){ _ = resp.Body.Close() }()
- internal/cast/client_test.go: prefix all json.Decode/Encode calls with _ =
- internal/ghl/oauth_test.go: _ = r.ParseForm(), _, _ = w.Write(...)

golangci-lint exclusion rules in v2 are not suppressing test file errcheck
as expected, so fixes are applied directly in source.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/cast/client_test.go

@@ -22,12 +22,12 @@ func TestSendSMS_Success(t *testing.T) {
 			t.Errorf("expected X-API-Key cast_testkey, got %s", r.Header.Get("X-API-Key"))
 		}
 		var body SendRequest
-		json.NewDecoder(r.Body).Decode(&body)
+		_ = json.NewDecoder(r.Body).Decode(&body)
 		if body.To != "09171234567" {
 			t.Errorf("expected to=09171234567, got %s", body.To)
 		}
 		w.WriteHeader(http.StatusOK)
-		json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "abc123", Parts: 1})
+		_ = json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "abc123", Parts: 1})
 	}))
 	defer srv.Close()
 
@@ -44,7 +44,7 @@ func TestSendSMS_Success(t *testing.T) {
 func TestSendSMS_APIError(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusPaymentRequired)
-		json.NewEncoder(w).Encode(SendResponse{Success: false, Error: "insufficient credits"})
+		_ = json.NewEncoder(w).Encode(SendResponse{Success: false, Error: "insufficient credits"})
 	}))
 	defer srv.Close()
 
@@ -65,7 +65,7 @@ func TestSendSMS_APIError(t *testing.T) {
 func TestSendSMS_SuccessFalseInBody(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
-		json.NewEncoder(w).Encode(SendResponse{Success: false, Error: "invalid number"})
+		_ = json.NewEncoder(w).Encode(SendResponse{Success: false, Error: "invalid number"})
 	}))
 	defer srv.Close()
 
@@ -86,12 +86,12 @@ func TestSendSMS_SuccessFalseInBody(t *testing.T) {
 func TestSendSMS_WithSenderID(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		var body SendRequest
-		json.NewDecoder(r.Body).Decode(&body)
+		_ = json.NewDecoder(r.Body).Decode(&body)
 		if body.SenderID != "CAST" {
 			t.Errorf("expected sender_id=CAST, got %q", body.SenderID)
 		}
 		w.WriteHeader(http.StatusOK)
-		json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "x1", Parts: 1})
+		_ = json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "x1", Parts: 1})
 	}))
 	defer srv.Close()
 
@@ -105,12 +105,12 @@ func TestSendSMS_WithSenderID(t *testing.T) {
 func TestSendSMS_WithoutSenderID(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		var rawBody map[string]interface{}
-		json.NewDecoder(r.Body).Decode(&rawBody)
+		_ = json.NewDecoder(r.Body).Decode(&rawBody)
 		if _, ok := rawBody["sender_id"]; ok {
 			t.Error("sender_id should be omitted when empty")
 		}
 		w.WriteHeader(http.StatusOK)
-		json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "x2", Parts: 1})
+		_ = json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "x2", Parts: 1})
 	}))
 	defer srv.Close()
 
@@ -125,7 +125,7 @@ func TestSendSMS_WithoutSenderID(t *testing.T) {
 func TestSendSMS_Unauthorized(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnauthorized)
-		json.NewEncoder(w).Encode(SendResponse{Success: false, Error: "invalid api key"})
+		_ = json.NewEncoder(w).Encode(SendResponse{Success: false, Error: "invalid api key"})
 	}))
 	defer srv.Close()
 
@@ -153,7 +153,7 @@ func TestSendSMS_RetryOn429(t *testing.T) {
 			return
 		}
 		w.WriteHeader(http.StatusOK)
-		json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "retry-ok", Parts: 1})
+		_ = json.NewEncoder(w).Encode(SendResponse{Success: true, MessageID: "retry-ok", Parts: 1})
 	}))
 	defer srv.Close()
 

internal/ghl/oauth.go

@@ -183,7 +183,7 @@ func (h *OAuthHandler) postToken(ctx context.Context, data url.Values) (*TokenRe
 	if err != nil {
 		return nil, err
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return nil, err

internal/ghl/oauth_test.go

@@ -111,7 +111,7 @@ func TestGetValidToken_NotFound(t *testing.T) {
 func TestGetValidToken_Expired_RefreshesAutomatically(t *testing.T) {
 	// Mock GHL token endpoint that returns a fresh token on refresh
 	tokenSrv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		r.ParseForm()
+		_ = r.ParseForm()
 		if r.FormValue("grant_type") != "refresh_token" {
 			t.Errorf("expected refresh_token grant, got %s", r.FormValue("grant_type"))
 		}
@@ -154,7 +154,7 @@ func TestGetValidToken_Expired_RefreshFails(t *testing.T) {
 	// Simulate token endpoint failure during refresh
 	tokenSrv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnauthorized)
-		w.Write([]byte(`{"error":"invalid_grant"}`))
+		_, _ = w.Write([]byte(`{"error":"invalid_grant"}`))
 	}))
 	defer tokenSrv.Close()