Replace app content on a draft

Alpha. The app sub-resource may change shape without a deprecation cycle while apps mature. The document routes are stable.

Replace the app HTML on an existing draft — creating the app when the draft is workbook-only — optionally replacing the app settings in the same call. Operates only on the draft named by draftIdentifier, which the caller creates first via PATCH …/draft; a published app is never addressable for writing, so every edit is draft-then-publish by construction. No auto-publish — publish via POST …/draft/publish.

Last-write-wins, like every app write in the UI: the body is applied as given, with no expected-version precondition. Every write appends an immutable app_history revision, so nothing is lost — only the head moves.

Writes never reject on host policy. External <script src> / <link rel="stylesheet"> hosts outside the organization’s app policy (resolved over the settings this write produces) come back as non-blocking warnings — the render-time CSP is the enforcement, and a disallowed host is inert until an org admin allows it.

A document carries at most one of a dashboard or an app — never both; workbook-only is valid. The app HTML and settings live only at the app sub-resource routes; the document read carries an app slice pointing here, and the whole-document PATCH accepts that slice back only as it was read.