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

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

packages/core/src/index.ts

@@ -11,6 +11,11 @@ export type {
   TFunction,
 } from "./context.ts";
 export { createContext, withContextHeaders } from "./context.ts";
+export {
+  runWithRequestContext,
+  getRequestContext,
+  requireRequestContext,
+} from "./request-context.ts";
 export { createExecutionContext, executionContextFromHttp } from "./execution-context.ts";
 export type {
   ExecutionContext,

packages/core/src/request-context.ts

@@ -0,0 +1,33 @@
+import { AsyncLocalStorage } from "node:async_hooks";
+import type { Context } from "./context.ts";
+
+/**
+ * The request context for the currently executing server work.
+ *
+ * A server-side API call needs the request's cookies, session, and URL, but
+ * `ctx` is not in scope everywhere server code runs: load blocks have it,
+ * schema actions take it as a parameter, and plain actions and server
+ * functions have neither. Threading it through every signature would make the
+ * call site differ between server and browser, which defeats the point.
+ */
+const storage = new AsyncLocalStorage<Context>();
+
+export function runWithRequestContext<T>(ctx: Context, fn: () => T): T {
+  return storage.run(ctx, fn);
+}
+
+export function getRequestContext(): Context | undefined {
+  return storage.getStore();
+}
+
+export function requireRequestContext(what: string): Context {
+  const ctx = storage.getStore();
+
+  if (!ctx) {
+    throw new Error(
+      `${what} needs a request context. It ran outside a request — server-side API calls are only available while handling one.`,
+    );
+  }
+
+  return ctx;
+}