fix: preserve complete MCP call tool results

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: eyesofish

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

@@ -131,8 +131,11 @@ protected static Map<String, Object> wrapCallResult(
       return ImmutableMap.of("error", errorMessage);
     }
 
+    Map<String, Object> resultMap =
+        objectMapper.convertValue(callResult, new TypeReference<Map<String, Object>>() {});
+
     if (contents == null || contents.isEmpty()) {
-      return ImmutableMap.of();
+      return resultMap;
     }
 
     List<String> textOutputs = new ArrayList<>();
@@ -145,11 +148,7 @@ protected static Map<String, Object> wrapCallResult(
     }
 
     if (textOutputs.isEmpty()) {
-      return ImmutableMap.of(
-          "error",
-          "Tool '" + mcpToolName + "' returned content that is not TextContent.",
-          "content_details",
-          contents.toString());
+      return resultMap;
     }
 
     List<Map<String, Object>> resultMaps = new ArrayList<>();
@@ -161,6 +160,7 @@ protected static Map<String, Object> wrapCallResult(
         resultMaps.add(ImmutableMap.of("text", textOutput));
       }
     }
-    return ImmutableMap.of("text_output", resultMaps);
+    resultMap.put("text_output", resultMaps);
+    return resultMap;
   }
 }

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

@@ -25,6 +25,7 @@
 import io.modelcontextprotocol.client.McpSyncClient;
 import io.modelcontextprotocol.spec.McpSchema;
 import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
+import io.modelcontextprotocol.spec.McpSchema.ImageContent;
 import io.modelcontextprotocol.spec.McpSchema.TextContent;
 import java.util.List;
 import java.util.Map;
@@ -53,14 +54,61 @@ public void testWrapCallResult_success() {
 
     Map<String, Object> map = AbstractMcpTool.wrapCallResult(objectMapper, "my_tool", result);
 
+    assertThat(map).containsEntry("isError", false);
     assertThat(map).containsKey("text_output");
-    List<?> content = (List<?>) map.get("text_output");
-    assertThat(content).hasSize(1);
+    List<?> textOutput = (List<?>) map.get("text_output");
+    assertThat(textOutput).hasSize(1);
 
-    Map<?, ?> contentItem = (Map<?, ?>) content.get(0);
+    Map<?, ?> contentItem = (Map<?, ?>) textOutput.get(0);
     assertThat(contentItem).containsEntry("text", "success");
   }
 
+  @Test
+  public void testWrapCallResult_mixedContent_success() {
+    CallToolResult result =
+        new CallToolResult(
+            ImmutableList.of(
+                new TextContent("first"), new ImageContent(null, "aW1hZ2U=", "image/png", null)),
+            false,
+            Map.of("count", 2),
+            Map.of("traceId", "trace-123"));
+
+    Map<String, Object> map = AbstractMcpTool.wrapCallResult(objectMapper, "my_tool", result);
+
+    assertThat(map).containsEntry("isError", false);
+    assertThat(map).containsEntry("structuredContent", Map.of("count", 2));
+    assertThat(map).containsEntry("_meta", Map.of("traceId", "trace-123"));
+
+    List<?> content = (List<?>) map.get("content");
+    assertThat(content).hasSize(2);
+    Map<?, ?> textContent = (Map<?, ?>) content.get(0);
+    assertThat(textContent).containsEntry("type", "text");
+    assertThat(textContent).containsEntry("text", "first");
+    Map<?, ?> imageContent = (Map<?, ?>) content.get(1);
+    assertThat(imageContent).containsEntry("type", "image");
+    assertThat(imageContent).containsEntry("data", "aW1hZ2U=");
+    assertThat(imageContent).containsEntry("mimeType", "image/png");
+
+    List<?> textOutput = (List<?>) map.get("text_output");
+    assertThat(textOutput).containsExactly(Map.of("text", "first"));
+  }
+
+  @Test
+  public void testWrapCallResult_nonTextContent_success() {
+    CallToolResult result =
+        new CallToolResult(
+            ImmutableList.of(new ImageContent(null, "aW1hZ2U=", "image/png", null)),
+            false,
+            null,
+            null);
+
+    Map<String, Object> map = AbstractMcpTool.wrapCallResult(objectMapper, "my_tool", result);
+
+    assertThat(map).doesNotContainKey("error");
+    assertThat(map).containsEntry("isError", false);
+    assertThat((List<?>) map.get("content")).hasSize(1);
+  }
+
   @Test
   public void instantiateWithToolBuilder_nullDescription_succeeds() {
     McpSyncClient sessionMock = mock(McpSyncClient.class);