feat(httpclient)!: promote to v1.0.0 — retry-on-429 with Retry-After, DoJSONRequest, bump deps

Extend retry loop to handle HTTP 429 Too Many Requests: when the server includes a
Retry-After header, that duration is used as the retry delay; otherwise falls back to
the configured BackOffDelay. Add DoJSONRequest[Req, Resp] free function that serialises
the request body as JSON, sets Content-Type, and delegates response decoding to DoJSON.
Bump logz and xerrors from v0.9.0 to v1.0.0. API committed as stable.

httpclient_test.go

@@ -111,6 +111,96 @@ func TestClient_Do_NoRequestID(t *testing.T) {
 	}
 }
 
+func TestClient_Do_Retry429_WithRetryAfter(t *testing.T) {
+	calls := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		calls++
+		w.Header().Set("Retry-After", "0")
+		w.WriteHeader(http.StatusTooManyRequests)
+	}))
+	defer srv.Close()
+
+	client := New(newLogger(), Config{
+		Name: "test", Timeout: 5 * time.Second, DialTimeout: 2 * time.Second,
+		MaxRetries: 3, RetryDelay: 1 * time.Millisecond, CBThreshold: 100, CBTimeout: time.Minute,
+	})
+	req, _ := http.NewRequest(http.MethodGet, srv.URL, nil)
+	_, err := client.Do(req)
+	if err == nil {
+		t.Fatal("expected error after retries")
+	}
+	if calls < 2 {
+		t.Errorf("expected retries on 429, got %d calls", calls)
+	}
+}
+
+func TestClient_Do_Retry429_NoRetryAfter(t *testing.T) {
+	calls := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		calls++
+		w.WriteHeader(http.StatusTooManyRequests)
+	}))
+	defer srv.Close()
+
+	client := New(newLogger(), Config{
+		Name: "test", Timeout: 5 * time.Second, DialTimeout: 2 * time.Second,
+		MaxRetries: 3, RetryDelay: 1 * time.Millisecond, CBThreshold: 100, CBTimeout: time.Minute,
+	})
+	req, _ := http.NewRequest(http.MethodGet, srv.URL, nil)
+	_, err := client.Do(req)
+	if err == nil {
+		t.Fatal("expected error after retries")
+	}
+	if calls < 2 {
+		t.Errorf("expected retries on 429, got %d calls", calls)
+	}
+}
+
+func TestDoJSONRequest_Success(t *testing.T) {
+	type payload struct{ Name string }
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if ct := r.Header.Get("Content-Type"); ct != "application/json" {
+			t.Errorf("want Content-Type application/json, got %q", ct)
+		}
+		var req payload
+		_ = json.NewDecoder(r.Body).Decode(&req)
+		_ = json.NewEncoder(w).Encode(payload{Name: "echo:" + req.Name})
+	}))
+	defer srv.Close()
+
+	client := New(newLogger(), Config{
+		Name: "test", Timeout: 5 * time.Second, DialTimeout: 2 * time.Second,
+		MaxRetries: 1, RetryDelay: time.Millisecond, CBThreshold: 10, CBTimeout: time.Minute,
+	})
+	result, err := DoJSONRequest[payload, payload](t.Context(), client, http.MethodPost, srv.URL, payload{Name: "alice"})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if result.Name != "echo:alice" {
+		t.Errorf("want echo:alice, got %s", result.Name)
+	}
+}
+
+func TestDoJSONRequest_4xx(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+	}))
+	defer srv.Close()
+
+	client := New(newLogger(), Config{
+		Name: "test", Timeout: 5 * time.Second, DialTimeout: 2 * time.Second,
+		MaxRetries: 1, RetryDelay: time.Millisecond, CBThreshold: 10, CBTimeout: time.Minute,
+	})
+	_, err := DoJSONRequest[struct{}, struct{}](t.Context(), client, http.MethodPost, srv.URL, struct{}{})
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	var xe *xerrors.Err
+	if !errors.As(err, &xe) || xe.Code() != xerrors.ErrNotFound {
+		t.Errorf("want ErrNotFound, got %v", err)
+	}
+}
+
 func TestDoJSON_Success(t *testing.T) {
 	type payload struct{ Name string }
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {