refactor(core): Centralize tool response formatting (#743)

2 files changed, 9 insertions, 7 deletions

diff --git a/packages/core/src/tools/mcp-tool.test.ts b/packages/core/src/tools/mcp-tool.test.ts
index 86968b3d..fc6ce6be 100644
--- a/packages/core/src/tools/mcp-tool.test.ts
+++ b/packages/core/src/tools/mcp-tool.test.ts
@@ -138,12 +138,7 @@ describe('DiscoveredMCPTool', () => {
       const stringifiedResponseContent = JSON.stringify(
         mockToolSuccessResultObject,
       );
-      // getStringifiedResultForDisplay joins text parts, then wraps the array of processed parts in JSON
-      const expectedDisplayOutput =
-        '```json\n' +
-        JSON.stringify([stringifiedResponseContent], null, 2) +
-        '\n```';
-      expect(toolResult.returnDisplay).toBe(expectedDisplayOutput);
+      expect(toolResult.returnDisplay).toBe(stringifiedResponseContent);
     });
 
     it('should handle empty result from getStringifiedResultForDisplay', async () => {
diff --git a/packages/core/src/tools/mcp-tool.ts b/packages/core/src/tools/mcp-tool.ts
index 65c0cae8..8a7694d8 100644
--- a/packages/core/src/tools/mcp-tool.ts
+++ b/packages/core/src/tools/mcp-tool.ts
@@ -149,6 +149,13 @@ function getStringifiedResultForDisplay(result: Part[]) {
     return part; // Fallback for unexpected structure or non-FunctionResponsePart
   };
 
-  const processedResults = result.map(processFunctionResponse);
+  const processedResults =
+    result.length === 1
+      ? processFunctionResponse(result[0])
+      : result.map(processFunctionResponse);
+  if (typeof processedResults === 'string') {
+    return processedResults;
+  }
+
   return '```json\n' + JSON.stringify(processedResults, null, 2) + '\n```';
 }