feat(send): browser extension that clips pages into Readest as EPUBs (#4266)

Replaces the URL-only placeholder extension with a full MV3 page-clipper
that builds a self-contained EPUB on the user's machine and uploads it
to the inbox.

- Captures the rendered DOM in a content script, then runs Readability,
  asset bundling, and EPUB build through the shared
  `convertToEpub({kind: 'page'})` pipeline inside a Chrome offscreen
  document (the SW lacks DOMParser).
- Uploads the resulting EPUB directly from the offscreen page to the
  new `POST /api/send/inbox/file` endpoint — keeps the bytes in one
  realm because `runtime.sendMessage` JSON-serialises ArrayBuffer to
  `{}` between extension contexts.
- Adds a long-lived Port + ping handshake between SW, offscreen, and
  the on-demand capture content script so neither idle-eviction nor
  load-order races can hang the popup.
- Localised popup, badge feedback, key-as-content i18n (`_('English source')`)
  with an extract script that seeds locale stubs from i18n-langs.json
  and writes a static-imports map for the runtime. All 33 locales
  fully translated.
- Server: `pages/api/send/inbox/file.ts` accepts a raw EPUB body
  (Content-Type: application/epub+zip), enforces the inbox pending cap,
  stores to the existing send-inbox R2 bucket as `kind='file'`.
  `assetBundler` now sets `credentials: 'include'` in the non-Tauri
  branch so the extension SW carries paywalled-CDN cookies.
- 47 vitest cases for the extension shell (upload, badge, auth, lazy,
  popup state machine, auth-bridge token sync) + 8 cases for the new
  server endpoint. CI's `test_web_app` invokes both via the extended
  `test:pr:web` plus a `build-browser-ext` step that catches webpack
  alias / Tauri-stub regressions.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/readest-app/src/services/constants.ts

@@ -753,6 +753,12 @@ export const SHARE_EXPIRATION_DAYS = [1, 3, 7] as const;
 export const SEND_EMAIL_DOMAIN = 'readest.com';
 export const SEND_INBOX_BUCKET = 'readest-send-inbox';
 export const SEND_INBOX_PENDING_LIMIT = 50;
+// Hard cap on the size of a single uploaded EPUB the browser extension can
+// drop into the inbox. 30 MB is the same total-asset cap the client-side
+// bundler enforces — plus a bit of head-room for chapter HTML / structural
+// overhead. Beyond this size a clipped article is almost certainly an
+// over-illustrated page that would never read well in the EPUB anyway.
+export const SEND_INBOX_FILE_MAX_BYTES = 40 * 1024 * 1024;
 export const SHARE_DEFAULT_EXPIRATION_DAYS = 3;
 export const SHARE_MAX_PER_USER = 50;
 export const SHARE_TOKEN_LENGTH = 22;

apps/readest-app/src/services/send/conversion/assetBundler.ts

@@ -5,12 +5,18 @@ import type { EpubImage } from './types';
 
 // On Tauri we go through the Rust HTTP client (no browser-CORS); on web
 // we use the native fetch — the bundler is only ever invoked from a
-// CORS-free caller there (the future extension's content script). In
-// Tauri we also fold in the full image-fetch header set (UA + Sec-Ch-Ua +
-// Sec-Fetch-* + Referer) so CDNs that gate images on the browser shape
-// — NYT, WSJ, paywalled CDNs — cooperate.
+// CORS-free caller there (the browser extension's service worker, which
+// has broad `host_permissions`). In the non-Tauri path we set
+// `credentials: 'include'` so the browser sends the user's cookies for
+// paywalled / member-only CDN hosts — without that, an authenticated
+// Substack image returns a placeholder. In Tauri we also fold in the
+// full image-fetch header set (UA + Sec-Ch-Ua + Sec-Fetch-* + Referer)
+// so CDNs that gate images on the browser shape — NYT, WSJ, paywalled
+// CDNs — cooperate.
 const httpFetch = (url: string, referer: string | null, init?: RequestInit): Promise<Response> => {
-  if (!isTauriAppPlatform()) return globalThis.fetch(url, init);
+  if (!isTauriAppPlatform()) {
+    return globalThis.fetch(url, { credentials: 'include', ...init });
+  }
   const baseHeaders = imageFetchHeaders(referer);
   const headers = new Headers(init?.headers);
   for (const [k, v] of Object.entries(baseHeaders)) {