feat: refine operations UI and transport limits

gateway/internal/inbound/transport.go

@@ -12,6 +12,8 @@ import (
 	"time"
 )
 
+const maxAPIResponseBodyBytes int64 = 4 * 1024 * 1024
+
 func (s Server) post(ctx context.Context, path string, payload any, result any) error {
 	client := s.HTTPClient
 	if client == nil {
@@ -31,10 +33,17 @@ func (s Server) post(ctx context.Context, path string, payload any, result any)
 		return err
 	}
 	defer resp.Body.Close()
-	responseBody, err := io.ReadAll(io.LimitReader(resp.Body, 64*1024))
+	// Read one byte beyond the supported boundary so an oversized upstream
+	// response is reported explicitly. Silently cutting JSON at the boundary
+	// turns a transport-capacity problem into a misleading syntax error and can
+	// leave recoverable downstream receipts stuck indefinitely.
+	responseBody, err := io.ReadAll(io.LimitReader(resp.Body, maxAPIResponseBodyBytes+1))
 	if err != nil {
 		return fmt.Errorf("read api response: %w", err)
 	}
+	if int64(len(responseBody)) > maxAPIResponseBodyBytes {
+		return fmt.Errorf("api response exceeds %d-byte limit", maxAPIResponseBodyBytes)
+	}
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 		detail := strings.TrimSpace(string(responseBody))
 		if detail == "" {

gateway/internal/inbound/transport_test.go

@@ -0,0 +1,46 @@
+package inbound
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestPostAcceptsAPIResponseLargerThanLegacy64KiB(t *testing.T) {
+	payload := strings.Repeat("x", 128*1024)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]string{"payload": payload})
+	}))
+	defer server.Close()
+
+	var result struct {
+		Payload string `json:"payload"`
+	}
+	if err := (Server{APIBaseURL: server.URL}).post(context.Background(), "/large", map[string]string{"request": "ok"}, &result); err != nil {
+		t.Fatalf("post response larger than 64KiB: %v", err)
+	}
+	if result.Payload != payload {
+		t.Fatalf("payload length = %d, want %d", len(result.Payload), len(payload))
+	}
+}
+
+func TestPostRejectsAPIResponseBeyondFourMiBWithoutTruncatedJSONError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"payload":"` + strings.Repeat("x", int(maxAPIResponseBodyBytes)) + `"}`))
+	}))
+	defer server.Close()
+
+	var result map[string]any
+	err := (Server{APIBaseURL: server.URL}).post(context.Background(), "/too-large", map[string]string{"request": "ok"}, &result)
+	if err == nil || !strings.Contains(err.Error(), "api response exceeds 4194304-byte limit") {
+		t.Fatalf("error = %v, want explicit response-size error", err)
+	}
+	if strings.Contains(err.Error(), "unexpected end of JSON input") {
+		t.Fatalf("oversized response must not surface as truncated JSON: %v", err)
+	}
+}