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packages/foundation/data/packer-browser/src/utils/cross-origin.md

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+# `cross-origin` — multi-origin Service Worker registration
+
+## Purpose
+
+`registerCrossOriginPackedResourceServiceWorker` lets an application
+register a packed-resource Service Worker hosted on a different origin
+(typically a CDN subdomain). Before any browser request is dispatched
+the helper validates the SW URL's origin against a caller-supplied
+allowlist, so attacker-controlled or misconfigured CDN origins cannot
+slip past. On success the helper returns both the new registration and
+the container's current registration list so multi-tenant apps can
+confirm the CDN-origin SW is actually controlling the page.
+
+## Features
+
+- Strict allowlist validation BEFORE `register()` fires
+- Parses `swUrl` via the `URL` constructor — malformed URLs reject with
+  `PACKER_BROWSER.UNAUTHORIZED_ORIGIN`
+- Delegates to `registerPackedResourceServiceWorker` so all the
+  underlying contract (AbortSignal, error wrapping, message resolution)
+  remains intact
+- Returns the full registration list (parity with
+  `clients.matchAll({ includeUncontrolled: true })`)
+
+## Usage: Basic
+
+```ts
+import { registerCrossOriginPackedResourceServiceWorker } from "@suaveplan/packer-browser/utils";
+
+await registerCrossOriginPackedResourceServiceWorker({
+    swUrl: "https://cdn.example.com/sw.js",
+    scope: "/packed/",
+    allowedOrigins: ["https://cdn.example.com"],
+});
+```
+
+## Usage: Advanced
+
+```ts
+import {
+    PACKER_BROWSER_CODES,
+    PackerBrowserError,
+    registerCrossOriginPackedResourceServiceWorker,
+} from "@suaveplan/packer-browser";
+
+try {
+    const { registration, registrations } =
+        await registerCrossOriginPackedResourceServiceWorker({
+            swUrl: "https://cdn.example.com/sw.js",
+            scope: "/",
+            allowedOrigins: [
+                "https://cdn.example.com",
+                "https://cdn-fallback.example.com",
+            ],
+            container: navigator.serviceWorker,
+            signal: shutdownController.signal,
+        });
+    console.log("registered", registration.scope, "of", registrations.length);
+} catch (err) {
+    if (
+        err instanceof PackerBrowserError &&
+        err.code === PACKER_BROWSER_CODES.UNAUTHORIZED_ORIGIN
+    ) {
+        console.warn("Origin not allowed; falling back to first-party SW.");
+    }
+}
+```
+
+## API Reference
+
+- `registerCrossOriginPackedResourceServiceWorker(opts: RegisterCrossOriginOptions): Promise<RegisterCrossOriginResult>`
+  - `opts.swUrl: string` — absolute SW URL. Required.
+  - `opts.scope: string` — registration scope. Required.
+  - `opts.allowedOrigins: ReadonlyArray<string>` — exact-string match. Required.
+  - `opts.container?` — injectable container. Default: `navigator.serviceWorker`.
+  - `opts.messageResolver?` — i18n resolver.
+  - `opts.signal?` — AbortSignal forwarded to `register()`.
+  - Returns `{ registration, registrations }`.
+
+## Implementation Notes
+
+- Origin equality is exact-string — there is no host-suffix matching.
+  Allowlisting both `https://cdn.example.com` and
+  `https://cdn-fallback.example.com` is explicit by design.
+- Malformed `swUrl` strings (relative paths, plain identifiers) yield
+  `UNAUTHORIZED_ORIGIN`, not `SW_REGISTRATION_FAILED`, because the
+  helper deliberately rejects before consulting the container.
+- The `registrations` list is the full `container.getRegistrations()`
+  return value when a container is supplied; without one (e.g. in a
+  Node smoke harness) the underlying `register()` already rejects with
+  `SW_REGISTRATION_FAILED` so the caller never sees a partial list.