fix: update RestErrorMapper to handle RFC 7807 Problem Details error format

This covers the core fix: the client's RestErrorMapper now reads the type URI
from Problem Details responses (introduced by the server-side changes on this branch)
instead of the old error/message fields, with backward compatibility for the legacy format.

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>

Author: ehsavoie

client/transport/rest/src/main/java/io/a2a/client/transport/rest/RestErrorMapper.java

@@ -36,18 +36,63 @@ public static A2AClientException mapRestError(String body, int code) {
         try {
             if (body != null && !body.isBlank()) {
                 JsonObject node = JsonUtil.fromJson(body, JsonObject.class);
+                // Support RFC 7807 Problem Details format (type, title, details, status)
+                if (node.has("type")) {
+                    String type = node.get("type").getAsString();
+                    String errorMessage = node.has("title") ? node.get("title").getAsString() : "";
+                    return mapRestErrorByType(type, errorMessage, code);
+                }
+                // Legacy format (error, message)
                 String className = node.has("error") ? node.get("error").getAsString() : "";
                 String errorMessage = node.has("message") ? node.get("message").getAsString() : "";
-                return mapRestError(className, errorMessage, code);
+                return mapRestErrorByClassName(className, errorMessage, code);
             }
-            return mapRestError("", "", code);
+            return mapRestErrorByClassName("", "", code);
         } catch (JsonProcessingException ex) {
             Logger.getLogger(RestErrorMapper.class.getName()).log(Level.SEVERE, null, ex);
             return new A2AClientException("Failed to parse error response: " + ex.getMessage());
         }
     }
 
     public static A2AClientException mapRestError(String className, String errorMessage, int code) {
+        return mapRestErrorByClassName(className, errorMessage, code);
+    }
+
+    /**
+     * Maps RFC 7807 Problem Details error type URIs to A2A exceptions.
+     * <p>
+     * Note: Error constructors receive null for code and data parameters because:
+     * <ul>
+     *   <li>Error codes are defaulted by each error class (e.g., -32007 for ExtendedAgentCardNotConfiguredError)</li>
+     *   <li>The message comes from the RFC 7807 "title" field</li>
+     *   <li>The data field is optional and not included in basic RFC 7807 responses</li>
+     * </ul>
+     *
+     * @param type the RFC 7807 error type URI (e.g., "https://a2a-protocol.org/errors/task-not-found")
+     * @param errorMessage the error message from the "title" field
+     * @param code the HTTP status code (currently unused, kept for consistency)
+     * @return an A2AClientException wrapping the appropriate A2A error
+     */
+    private static A2AClientException mapRestErrorByType(String type, String errorMessage, int code) {
+        return switch (type) {
+            case "https://a2a-protocol.org/errors/task-not-found" -> new A2AClientException(errorMessage, new TaskNotFoundError());
+            case "https://a2a-protocol.org/errors/extended-agent-card-not-configured" -> new A2AClientException(errorMessage, new ExtendedAgentCardNotConfiguredError(null, errorMessage, null));
+            case "https://a2a-protocol.org/errors/content-type-not-supported" -> new A2AClientException(errorMessage, new ContentTypeNotSupportedError(null, errorMessage, null));
+            case "https://a2a-protocol.org/errors/internal-error" -> new A2AClientException(errorMessage, new InternalError(errorMessage));
+            case "https://a2a-protocol.org/errors/invalid-agent-response" -> new A2AClientException(errorMessage, new InvalidAgentResponseError(null, errorMessage, null));
+            case "https://a2a-protocol.org/errors/invalid-params" -> new A2AClientException(errorMessage, new InvalidParamsError());
+            case "https://a2a-protocol.org/errors/invalid-request" -> new A2AClientException(errorMessage, new InvalidRequestError());
+            case "https://a2a-protocol.org/errors/method-not-found" -> new A2AClientException(errorMessage, new MethodNotFoundError());
+            case "https://a2a-protocol.org/errors/push-notification-not-supported" -> new A2AClientException(errorMessage, new PushNotificationNotSupportedError());
+            case "https://a2a-protocol.org/errors/task-not-cancelable" -> new A2AClientException(errorMessage, new TaskNotCancelableError());
+            case "https://a2a-protocol.org/errors/unsupported-operation" -> new A2AClientException(errorMessage, new UnsupportedOperationError());
+            case "https://a2a-protocol.org/errors/extension-support-required" -> new A2AClientException(errorMessage, new ExtensionSupportRequiredError(null, errorMessage, null));
+            case "https://a2a-protocol.org/errors/version-not-supported" -> new A2AClientException(errorMessage, new VersionNotSupportedError(null, errorMessage, null));
+            default -> new A2AClientException(errorMessage);
+        };
+    }
+
+    private static A2AClientException mapRestErrorByClassName(String className, String errorMessage, int code) {
         return switch (className) {
             case "io.a2a.spec.TaskNotFoundError" -> new A2AClientException(errorMessage, new TaskNotFoundError());
             case "io.a2a.spec.ExtendedCardNotConfiguredError" -> new A2AClientException(errorMessage, new ExtendedAgentCardNotConfiguredError(null, errorMessage, null));