Add Node.js low-level tool-definition E2E test [3/6] (#1725)

* Add Node.js low-level tool-definition E2E test

Related to issue #1682 but does not fix #1682.

Align low_level_tool_definition coverage with PR #1721 snapshot behavior by only defining tools exercised by the shared snapshot.

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

* Fix Node.js PR formatting and scope

- Apply Prettier formatting to tools.e2e.test.ts so Node ubuntu format check passes.

- Drop session lifecycle carryover from this PR by restoring Node session lifecycle files to upstream/main content, keeping this PR focused on low-level tool-definition coverage.

Related to issue #1682 but does not fix #1682.

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

---------

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

Author: edburns

nodejs/test/e2e/tools.e2e.test.ts

@@ -6,7 +6,7 @@ import { writeFile } from "fs/promises";
 import { join } from "path";
 import { assert, describe, expect, it } from "vitest";
 import { z } from "zod";
-import { defineTool, approveAll } from "../../src/index.js";
+import { defineTool, approveAll, ToolSet } from "../../src/index.js";
 import type { PermissionRequest } from "../../src/index.js";
 import { createSdkTestContext } from "./harness/sdkTestContext";
 
@@ -45,6 +45,54 @@ describe("Custom tools", async () => {
         expect(assistantMessage?.data.content).toContain("HELLO");
     });
 
+    it("low_level_tool_definition", async () => {
+        let currentPhase = "";
+        const session = await client.createSession({
+            onPermissionRequest: approveAll,
+            availableTools: new ToolSet().addCustom("*").addBuiltIn("web_fetch"),
+            tools: [
+                defineTool("set_current_phase", {
+                    description: "Sets the current phase of the agent",
+                    parameters: z.object({
+                        phase: z.enum(["searching", "analyzing", "done"]),
+                    }),
+                    handler: ({ phase }) => {
+                        currentPhase = phase;
+                        return `Phase set to ${phase}`;
+                    },
+                }),
+                defineTool("search_items", {
+                    description: "Search for items by keyword",
+                    parameters: z.object({
+                        keyword: z.string(),
+                    }),
+                    handler: (_args, invocation) => {
+                        const args = invocation.arguments as Record<string, unknown>;
+                        if (args.keyword !== "copilot") {
+                            throw new Error(
+                                `Expected keyword to be 'copilot', got: ${String(args.keyword)}`
+                            );
+                        }
+                        return "Found: item_alpha, item_beta";
+                    },
+                }),
+            ],
+        });
+
+        const assistantMessage = await session.sendAndWait({
+            prompt: "First, set the current phase to 'analyzing'. Then search for items with keyword 'copilot'. Report the phase and search results.",
+        });
+
+        const content = assistantMessage?.data.content ?? "";
+        expect(content.length).toBeGreaterThan(0);
+        expect(content.toLowerCase()).toContain("analyzing");
+        expect(
+            content.toLowerCase().includes("item_alpha") ||
+                content.toLowerCase().includes("item_beta")
+        ).toBe(true);
+        expect(currentPhase).toBe("analyzing");
+    });
+
     it("handles tool calling errors", async () => {
         const session = await client.createSession({
             onPermissionRequest: approveAll,