diff --git a/docs/library.md b/docs/library.md
index 59a8bfe..6444917 100644
--- a/docs/library.md
+++ b/docs/library.md
@@ -112,6 +112,29 @@ sakral (Religion & Mythologie), spiel (Kinder & Jugend), code (Informatik),
 typo, wellen, botanik, berge, zellen — and bauhaus when nothing matches. A hash
 of title and author picks palette, layout and every detail.
 
+### Eingang: books from a cloud folder by themselves (since 2026-10-24)
+
+A cloud source (Einstellungen → Cloud-Verbindungen, WebDAV: `accounts.WebDAVSource`,
+`accounts/webdav.py`) can be marked **Eingang**: its new books come into the library without
+anyone importing them. The server can't do it alone — the books are encrypted with the key
+on the devices — so a device does:
+
+1. `static/js/app/57-cloud-inbox.js`: after the book list has loaded (at most every 5
+   minutes; only with the real key in `localStorage`, never on diora Reader) it asks
+   `GET /books/cloud/inbox/` → `{files: [{source, label, path, name, size, modified}], errors}`:
+   the `.epub`/`.pdf` files of the Eingang sources (three folders deep) no device has taken.
+   The server claims them for this device for ten minutes (another device asking meanwhile
+   doesn't get them).
+2. Each file: fetched through the server (`/books/cloud/<id>/fetch/`), imported like any file
+   (`_importEbookBuffer`, `skipKnown`: same title and author → left out), then
+   `POST /books/cloud/<id>/done/ {path, result}` with `imported`, `known`, `too_big` (not
+   offered again) or `failed` (again once the claim ran out).
+3. The server keeps them in `accounts.WebDAVSeen` (source, path, size, modified): a file whose
+   size changed counts as new. The folder itself is never changed.
+
+The first such source: Shelfmark's e-book downloads on the Hetzner server, served read-only by
+dufs (set up by the "Media" session; its notes: `C:\Users\m\homelab-handoff\04-hoerbuecher.md`).
+
 ## Zeitschriften: das Heft und seine Artikel
 
 An issue is a unit (the editors' selection and order, its date, its theme) and