Address review feedback: restore Go fallback, add test, fix snapshot

- Go: restore fallback to fmt.Sprintf when TextResultForLLM is empty,
  preserving prior behavior for handlers that don't set it.
- Node: add e2e test verifying toolTelemetry is not leaked into LLM
  content and that the tool.execution_complete event fires.
- Update failure-resulttype snapshot to expect just textResultForLlm
  content instead of the old stringified JSON.

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

Author: Morabbin

go/session.go

@@ -620,9 +620,14 @@ func (s *Session) executeToolAndRespond(requestID, toolName, toolCallID string,
 		return
 	}
 
+	textResultForLLM := result.TextResultForLLM
+	if textResultForLLM == "" {
+		textResultForLLM = fmt.Sprintf("%v", result)
+	}
+
 	rpcResult := rpc.ResultUnion{
 		ResultResult: &rpc.ResultResult{
-			TextResultForLlm: result.TextResultForLLM,
+			TextResultForLlm: textResultForLLM,
 			ToolTelemetry:    result.ToolTelemetry,
 		},
 	}

nodejs/test/e2e/tool_results.test.ts

@@ -4,12 +4,12 @@
 
 import { describe, expect, it } from "vitest";
 import { z } from "zod";
-import type { ToolResultObject } from "../../src/index.js";
+import type { SessionEvent, ToolResultObject } from "../../src/index.js";
 import { approveAll, defineTool } from "../../src/index.js";
 import { createSdkTestContext } from "./harness/sdkTestContext";
 
 describe("Tool Results", async () => {
-    const { copilotClient: client } = await createSdkTestContext();
+    const { copilotClient: client, openAiEndpoint } = await createSdkTestContext();
 
     it("should handle structured ToolResultObject from custom tool", async () => {
         const session = await client.createSession({
@@ -98,4 +98,51 @@ describe("Tool Results", async () => {
 
         await session.disconnect();
     });
+
+    it("should preserve toolTelemetry and not stringify structured results for LLM", async () => {
+        const session = await client.createSession({
+            onPermissionRequest: approveAll,
+            tools: [
+                defineTool("analyze_code", {
+                    description: "Analyzes code for issues",
+                    parameters: z.object({
+                        file: z.string(),
+                    }),
+                    handler: ({ file }): ToolResultObject => ({
+                        textResultForLlm: `Analysis of ${file}: no issues found`,
+                        resultType: "success",
+                        toolTelemetry: {
+                            metrics: { analysisTimeMs: 150 },
+                            properties: { analyzer: "eslint" },
+                        },
+                    }),
+                }),
+            ],
+        });
+
+        const events: SessionEvent[] = [];
+        session.on((event) => events.push(event));
+
+        const assistantMessage = await session.sendAndWait({
+            prompt: "Analyze the file main.ts for issues.",
+        });
+
+        expect(assistantMessage?.data.content).toMatch(/no issues/i);
+
+        // Verify the LLM received just textResultForLlm, not stringified JSON
+        const traffic = await openAiEndpoint.getExchanges();
+        const lastConversation = traffic[traffic.length - 1]!;
+        const toolResults = lastConversation.request.messages.filter(
+            (m: { role: string }) => m.role === "tool"
+        );
+        expect(toolResults.length).toBe(1);
+        expect(toolResults[0]!.content).not.toContain("toolTelemetry");
+        expect(toolResults[0]!.content).not.toContain("resultType");
+
+        // Verify tool.execution_complete event carries toolTelemetry
+        const toolCompletes = events.filter((e) => e.type === "tool.execution_complete");
+        expect(toolCompletes.length).toBeGreaterThanOrEqual(1);
+
+        await session.disconnect();
+    });
 });

test/snapshots/tool_results/should_handle_tool_result_with_failure_resulttype.yaml

@@ -15,6 +15,6 @@ conversations:
               arguments: "{}"
       - role: tool
         tool_call_id: toolcall_0
-        content: '{"error":"API timeout","resultType":"failure","textResultForLlm":"Service unavailable"}'
+        content: Service unavailable
       - role: assistant
         content: service is down

test/snapshots/tool_results/should_preserve_tooltelemetry_and_not_stringify_structured_results_for_llm.yaml

@@ -0,0 +1,20 @@
+models:
+  - claude-sonnet-4.5
+conversations:
+  - messages:
+      - role: system
+        content: ${system}
+      - role: user
+        content: Analyze the file main.ts for issues.
+      - role: assistant
+        tool_calls:
+          - id: toolcall_0
+            type: function
+            function:
+              name: analyze_code
+              arguments: '{"file":"main.ts"}'
+      - role: tool
+        tool_call_id: toolcall_0
+        content: "Analysis of main.ts: no issues found"
+      - role: assistant
+        content: "The analysis of main.ts is complete -- no issues were found."