fix: handle listTasks status wire strings (#578)

What changed

  - Parse status in REST listTasks using TaskState.fromString
  - Return InvalidParamsError (422) for invalid status values
  - Add tests for valid wire strings and invalid status

  Why

- REST API expects wire strings like working / input-required, but
valueOf only accepts enum names, causing valid requests to return 500.

  Tests

```bash
mvn -pl transport/rest -am test
```
---

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Fixes #577  🦕

Author: hae02y

transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java

@@ -5,13 +5,15 @@
 
 import java.time.Instant;
 import java.time.format.DateTimeParseException;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Flow;
 import java.util.logging.Level;
 import java.util.logging.Logger;
+import java.util.stream.Collectors;
 
 import jakarta.enterprise.context.ApplicationScoped;
 import jakarta.enterprise.inject.Instance;
@@ -217,7 +219,21 @@ public HTTPRestResponse listTasks(@Nullable String contextId, @Nullable String s
                 paramsBuilder.contextId(contextId);
             }
             if (status != null) {
-                paramsBuilder.status(TaskState.valueOf(status));
+                try {
+                    paramsBuilder.status(TaskState.fromString(status));
+                } catch (IllegalArgumentException e) {
+                    try {
+                        paramsBuilder.status(TaskState.valueOf(status));
+                    } catch (IllegalArgumentException valueOfError) {
+                        String validStates = Arrays.stream(TaskState.values())
+                                .map(TaskState::asString)
+                                .collect(Collectors.joining(", "));
+                        Map<String, Object> errorData = new HashMap<>();
+                        errorData.put("parameter", "status");
+                        errorData.put("reason", "Must be one of: " + validStates);
+                        throw new InvalidParamsError(null, "Invalid params", errorData);
+                    }
+                }
             }
             if (pageSize != null) {
                 paramsBuilder.pageSize(pageSize);

transport/rest/src/test/java/io/a2a/transport/rest/handler/RestHandlerTest.java

@@ -58,6 +58,31 @@ public void testGetTaskNotFound() {
         Assertions.assertTrue(response.getBody().contains("TaskNotFoundError"));
     }
 
+    @Test
+    public void testListTasksStatusWireString() {
+        RestHandler handler = new RestHandler(CARD, requestHandler, internalExecutor);
+        taskStore.save(MINIMAL_TASK);
+
+        RestHandler.HTTPRestResponse response = handler.listTasks(null, "submitted", null, null,
+                null, null, null, "", callContext);
+
+        Assertions.assertEquals(200, response.getStatusCode());
+        Assertions.assertEquals("application/json", response.getContentType());
+        Assertions.assertTrue(response.getBody().contains(MINIMAL_TASK.id()));
+    }
+
+    @Test
+    public void testListTasksInvalidStatus() {
+        RestHandler handler = new RestHandler(CARD, requestHandler, internalExecutor);
+
+        RestHandler.HTTPRestResponse response = handler.listTasks(null, "not-a-status", null, null,
+                null, null, null, "", callContext);
+
+        Assertions.assertEquals(422, response.getStatusCode());
+        Assertions.assertEquals("application/json", response.getContentType());
+        Assertions.assertTrue(response.getBody().contains("InvalidParamsError"));
+    }
+
     @Test
     public void testSendMessage() throws InvalidProtocolBufferException {
         RestHandler handler = new RestHandler(CARD, requestHandler, internalExecutor);