fix(client): send json request headers

internal/client/client.go

@@ -78,6 +78,10 @@ func (c *Client) Do(method, path string, body interface{}, query url.Values) (*o
 	if err != nil {
 		return nil, err
 	}
+	req.Header.Set("Accept", "application/json")
+	if bodyReader != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
 
 	if c.Debug {
 		fmt.Printf("→ %s %s\n", method, fullURL)

internal/client/client_test.go

@@ -258,6 +258,12 @@ func TestClientDoWithBody(t *testing.T) {
 		if r.Method != "POST" {
 			t.Fatalf("expected POST, got %s", r.Method)
 		}
+		if got := r.Header.Get("Accept"); got != "application/json" {
+			t.Fatalf("Accept = %q, want application/json", got)
+		}
+		if got := r.Header.Get("Content-Type"); got != "application/json" {
+			t.Fatalf("Content-Type = %q, want application/json", got)
+		}
 		w.Header().Set("Content-Type", "application/json")
 		w.Write([]byte(`{"id":123}`))
 	}))
@@ -273,6 +279,25 @@ func TestClientDoWithBody(t *testing.T) {
 	}
 }
 
+func TestClientDoWithoutBodySetsAcceptOnly(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if got := r.Header.Get("Accept"); got != "application/json" {
+			t.Fatalf("Accept = %q, want application/json", got)
+		}
+		if got := r.Header.Get("Content-Type"); got != "" {
+			t.Fatalf("Content-Type = %q, want empty", got)
+		}
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{}`))
+	}))
+	defer server.Close()
+
+	c := &Client{HTTP: server.Client(), BaseURL: server.URL}
+	if _, err := c.Do("GET", "/api/test", nil, nil); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 func TestClientGet(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != "GET" {