fix: Use responseLength=-1 for empty-body status responses

sendResponseHeaders(code, 0) triggers chunked transfer encoding for
empty bodies; -1 is correct for status-only responses with no body.
Affects notFoundHandler and the NotFound/MethodNotAllowed/default
branches of defaultExceptionHandler.

Author: thced

src/main/java/com/retailsvc/http/Handlers.java

@@ -32,15 +32,15 @@ public static ExceptionHandler defaultExceptionHandler() {
             exchange.sendResponseHeaders(HTTP_BAD_REQUEST, body.length);
             exchange.getResponseBody().write(body);
           }
-          case NotFoundException _ -> exchange.sendResponseHeaders(HTTP_NOT_FOUND, 0);
+          case NotFoundException _ -> exchange.sendResponseHeaders(HTTP_NOT_FOUND, -1);
           case MethodNotAllowedException mna -> {
             String allow = mna.allowed().stream().map(Enum::name).collect(Collectors.joining(", "));
             exchange.getResponseHeaders().add("Allow", allow);
-            exchange.sendResponseHeaders(HTTP_BAD_METHOD, 0);
+            exchange.sendResponseHeaders(HTTP_BAD_METHOD, -1);
           }
           default -> {
             LOG.error("Unhandled exception in handler", t);
-            exchange.sendResponseHeaders(HTTP_INTERNAL_ERROR, 0);
+            exchange.sendResponseHeaders(HTTP_INTERNAL_ERROR, -1);
           }
         }
       } catch (IOException io) {
@@ -52,7 +52,7 @@ public static ExceptionHandler defaultExceptionHandler() {
   public static HttpHandler notFoundHandler() {
     return exchange -> {
       try (exchange) {
-        exchange.sendResponseHeaders(HTTP_NOT_FOUND, 0);
+        exchange.sendResponseHeaders(HTTP_NOT_FOUND, -1);
       }
     };
   }

src/test/java/com/retailsvc/http/HandlersDefaultExceptionTest.java

@@ -40,15 +40,15 @@ void validationExceptionRendersProblem() throws Exception {
   void notFoundReturns404() throws Exception {
     HttpExchange ex = newExchange(new ByteArrayOutputStream());
     Handlers.defaultExceptionHandler().handle(ex, new NotFoundException("GET /x"));
-    Mockito.verify(ex).sendResponseHeaders(404, 0);
+    Mockito.verify(ex).sendResponseHeaders(404, -1);
   }
 
   @Test
   void methodNotAllowedReturns405WithAllowHeader() throws Exception {
     HttpExchange ex = newExchange(new ByteArrayOutputStream());
     Handlers.defaultExceptionHandler()
         .handle(ex, new MethodNotAllowedException(Set.of(HttpMethod.GET, HttpMethod.POST)));
-    Mockito.verify(ex).sendResponseHeaders(405, 0);
+    Mockito.verify(ex).sendResponseHeaders(405, -1);
     assertThat(ex.getResponseHeaders().getFirst("Allow")).contains("GET").contains("POST");
   }
 }