fix(node): preserve AsyncLocalStorage context in unhandledRejection handlers

[bartlomieju]

Summary

• Fixes AsyncLocalStorage.getStore() returning undefined inside unhandledRejection / unhandledrejection event handlers
• Now matches Node.js behavior where the async context active at the time of rejection is preserved

Problem

import { AsyncLocalStorage } from 'node:async_hooks';
import process from 'node:process';

const store = new AsyncLocalStorage();

process.on('unhandledRejection', () => {
    console.log(store.getStore()); // Node: "data", Deno (before): undefined
});

await store.run("data", async () => {
    new Promise((_, reject) => setTimeout(() => reject(new Error('test')), 50));
});

Fix

The core fix is in deno_core (denoland/deno_core#1308):

1. Captures the async context (CPED) at promise rejection time in PromiseRejectWithNoHandler
2. Passes it alongside the promise/reason in the rejections array
3. Restores it before invoking the unhandled rejection handler in eventLoopTick

This PR adds the spec test. Once the deno_core PR is merged and the dependency is bumped, the test will pass.

Test plan

• Spec test node::async_local_storage_unhandled_rejection verifies the fix
• Manually verified with the reproduction script from the issue

Fixes #30135
Depends on denoland/deno_core#1308

🤖 Generated with Claude Code