fix: revert changes to AbstractMcpTool, maintaining backwards compatible text_output field in the response

core/src/main/java/com/google/adk/models/Claude.java

@@ -172,17 +172,11 @@ private ContentBlockParam partToAnthropicMessageBlock(Part part) {
       if (part.functionResponse().get().response().isPresent()) {
         Map<String, Object> responseData = part.functionResponse().get().response().get();
 
-        Object contentObj = responseData.get("content");
         Object resultObj = responseData.get("result");
-
-        if (contentObj instanceof List<?> list && !list.isEmpty()) {
-          // Native MCP format: list of content blocks
-          content = extractMcpContentBlocks(list);
-        } else if (resultObj != null) {
-          // ADK tool result object
-          content = resultObj instanceof String s ? s : serializeToJson(resultObj);
-        } else if (!responseData.isEmpty()) {
-          // Fallback: arbitrary JSON structure
+        if (resultObj != null) {
+          content = resultObj.toString();
+        } else {
+          // Fallback to json serialization of the function response.
           content = serializeToJson(responseData);
         }
       }
@@ -196,21 +190,6 @@ private ContentBlockParam partToAnthropicMessageBlock(Part part) {
     throw new UnsupportedOperationException("Not supported yet.");
   }
 
-  private String extractMcpContentBlocks(List<?> list) {
-    List<String> textBlocks = new ArrayList<>();
-    for (Object item : list) {
-      if (item instanceof Map<?, ?> m && "text".equals(m.get("type"))) {
-        Object textObj = m.get("text");
-        textBlocks.add(textObj != null ? String.valueOf(textObj) : "");
-      } else if (item instanceof String s) {
-        textBlocks.add(s);
-      } else {
-        textBlocks.add(serializeToJson(item));
-      }
-    }
-    return String.join("\n", textBlocks);
-  }
-
   private String serializeToJson(Object obj) {
     try {
       return JsonBaseModel.getMapper().writeValueAsString(obj);

core/src/main/java/com/google/adk/tools/mcp/AbstractMcpTool.java

@@ -16,16 +16,21 @@
 
 package com.google.adk.tools.mcp;
 
+import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.adk.tools.BaseTool;
 import com.google.adk.tools.mcp.McpToolException.McpToolDeclarationException;
 import com.google.common.collect.ImmutableMap;
 import com.google.genai.types.FunctionDeclaration;
 import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
+import io.modelcontextprotocol.spec.McpSchema.Content;
 import io.modelcontextprotocol.spec.McpSchema.JsonSchema;
+import io.modelcontextprotocol.spec.McpSchema.TextContent;
 import io.modelcontextprotocol.spec.McpSchema.Tool;
 import io.modelcontextprotocol.spec.McpSchema.ToolAnnotations;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 
@@ -110,7 +115,51 @@ protected static Map<String, Object> wrapCallResult(
     if (callResult == null) {
       return ImmutableMap.of("error", "MCP framework error: CallToolResult was null");
     }
+    List<Content> contents = callResult.content();
+    Boolean isToolError = callResult.isError();
 
-    return objectMapper.convertValue(callResult, new TypeReference<Map<String, Object>>() {});
+    if (isToolError != null && isToolError) {
+      String errorMessage = "Tool execution failed.";
+      if (contents != null
+          && !contents.isEmpty()
+          && contents.get(0) instanceof TextContent textContent) {
+        if (textContent.text() != null && !textContent.text().isEmpty()) {
+          errorMessage += " Details: " + textContent.text();
+        }
+      }
+      return ImmutableMap.of("error", errorMessage);
+    }
+
+    if (contents == null || contents.isEmpty()) {
+      return ImmutableMap.of();
+    }
+
+    List<String> textOutputs = new ArrayList<>();
+    for (Content content : contents) {
+      if (content instanceof TextContent textContent) {
+        if (textContent.text() != null) {
+          textOutputs.add(textContent.text());
+        }
+      }
+    }
+
+    if (textOutputs.isEmpty()) {
+      return ImmutableMap.of(
+          "error",
+          "Tool '" + mcpToolName + "' returned content that is not TextContent.",
+          "content_details",
+          contents.toString());
+    }
+
+    List<Map<String, Object>> resultMaps = new ArrayList<>();
+    for (String textOutput : textOutputs) {
+      try {
+        resultMaps.add(
+            objectMapper.readValue(textOutput, new TypeReference<Map<String, Object>>() {}));
+      } catch (JsonProcessingException e) {
+        resultMaps.add(ImmutableMap.of("text", textOutput));
+      }
+    }
+    return ImmutableMap.of("text_output", resultMaps);
   }
 }

core/src/test/java/com/google/adk/models/ClaudeTest.java

@@ -21,7 +21,6 @@
 import com.anthropic.client.AnthropicClient;
 import com.anthropic.models.messages.ContentBlockParam;
 import com.anthropic.models.messages.ToolResultBlockParam;
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.genai.types.FunctionResponse;
 import com.google.genai.types.Part;
@@ -51,11 +50,9 @@ public void setUp() throws Exception {
   }
 
   @Test
-  public void testPartToAnthropicMessageBlock_mcpNativeFormat() throws Exception {
+  public void testPartToAnthropicMessageBlock_mcpTool_legacyTextOutputKey() throws Exception {
     Map<String, Object> responseData =
-        ImmutableMap.of(
-            "content",
-            ImmutableList.of(ImmutableMap.of("type", "text", "text", "Extracted native MCP text")));
+        ImmutableMap.of("text_output", ImmutableMap.of("text", "Legacy result text"));
     FunctionResponse funcParam =
         FunctionResponse.builder().name("test_tool").response(responseData).id("call_123").build();
     Part part = Part.builder().functionResponse(funcParam).build();
@@ -64,21 +61,8 @@ public void testPartToAnthropicMessageBlock_mcpNativeFormat() throws Exception {
         (ContentBlockParam) partToAnthropicMessageBlockMethod.invoke(claude, part);
 
     ToolResultBlockParam toolResult = result.asToolResult();
-    assertThat(toolResult.content().get().asString()).isEqualTo("Extracted native MCP text");
-  }
-
-  @Test
-  public void testPartToAnthropicMessageBlock_legacyResultKey() throws Exception {
-    Map<String, Object> responseData = ImmutableMap.of("result", "Legacy result text");
-    FunctionResponse funcParam =
-        FunctionResponse.builder().name("test_tool").response(responseData).id("call_123").build();
-    Part part = Part.builder().functionResponse(funcParam).build();
-
-    ContentBlockParam result =
-        (ContentBlockParam) partToAnthropicMessageBlockMethod.invoke(claude, part);
-
-    ToolResultBlockParam toolResult = result.asToolResult();
-    assertThat(toolResult.content().get().asString()).isEqualTo("Legacy result text");
+    assertThat(toolResult.content().get().asString())
+        .isEqualTo("{\"text_output\":{\"text\":\"Legacy result text\"}}");
   }
 
   @Test

core/src/test/java/com/google/adk/tools/mcp/AbstractMcpToolTest.java

@@ -49,14 +49,11 @@ public void testWrapCallResult_success() {
 
     Map<String, Object> map = AbstractMcpTool.wrapCallResult(objectMapper, "my_tool", result);
 
-    assertThat(map).containsKey("content");
-    List<?> content = (List<?>) map.get("content");
+    assertThat(map).containsKey("text_output");
+    List<?> content = (List<?>) map.get("text_output");
     assertThat(content).hasSize(1);
 
     Map<?, ?> contentItem = (Map<?, ?>) content.get(0);
-    assertThat(contentItem).containsEntry("type", "text");
     assertThat(contentItem).containsEntry("text", "success");
-
-    assertThat(map).containsEntry("isError", false);
   }
 }