feat(core): carry the request context in an AsyncLocalStorage

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/core/test/request-context.test.ts

@@ -0,0 +1,49 @@
+import { expect, test } from "bun:test";
+import {
+  getRequestContext,
+  requireRequestContext,
+  runWithRequestContext,
+} from "../src/request-context.ts";
+
+const ctx = { marker: "the-request" } as never;
+
+test("the context is visible inside the run", () => {
+  runWithRequestContext(ctx, () => {
+    expect(getRequestContext()).toBe(ctx);
+  });
+});
+
+test("the context is visible across an await", async () => {
+  // The whole point is that it survives async boundaries a caller cannot see.
+  await runWithRequestContext(ctx, async () => {
+    await new Promise((resolve) => setTimeout(resolve, 1));
+    expect(getRequestContext()).toBe(ctx);
+  });
+});
+
+test("there is no context outside a run", () => {
+  expect(getRequestContext()).toBeUndefined();
+});
+
+test("requireRequestContext throws a message naming the caller", () => {
+  expect(() => requireRequestContext("api.searchUsers")).toThrow(/api\.searchUsers/);
+});
+
+test("concurrent runs do not see each other's context", async () => {
+  const first = { id: 1 } as never;
+  const second = { id: 2 } as never;
+  const seen: unknown[] = [];
+
+  await Promise.all([
+    runWithRequestContext(first, async () => {
+      await new Promise((resolve) => setTimeout(resolve, 5));
+      seen.push(getRequestContext());
+    }),
+    runWithRequestContext(second, async () => {
+      seen.push(getRequestContext());
+    }),
+  ]);
+
+  expect(seen).toContain(first);
+  expect(seen).toContain(second);
+});