feat(docs): export database documentation as standalone HTML

apps/desktop/src/docs-export/exportPayload.ts

@@ -0,0 +1,37 @@
+import type { AnnotationFile, SchemaSnapshot } from "@/docs/types";
+import type { ExportLocale } from "./exportTranslate";
+
+/**
+ * The contract between the exporter and this bundle.
+ *
+ * Task 6's Rust side serialises exactly this object as JSON, encodes it UTF-8
+ * then base64, and writes it as the text of
+ * `<script type="application/dbx-snapshot">`. Nothing else in the emitted
+ * document is read by the bundle.
+ *
+ * `lang` picks the starting locale only. The reader can change it — the
+ * person who exported the file is rarely the person who opens it.
+ */
+export interface ExportPayload {
+  snapshot: SchemaSnapshot;
+  annotations: AnnotationFile;
+  lang: ExportLocale;
+}
+
+/**
+ * Read the snapshot the exporter embedded in the document.
+ *
+ * This lives here rather than in `main.ts` so a spec can call it: importing
+ * `main.ts` mounts the application as a side effect. It is the whole of the
+ * contract with Task 6's Rust side, and the only thing in the emitted document
+ * the bundle reads.
+ */
+export function readPayload(): ExportPayload {
+  const node = document.querySelector("script[type='application/dbx-snapshot']");
+  if (node === null) throw new Error("no <script type='application/dbx-snapshot'> in this document");
+  // `atob` yields one byte per character; the payload is UTF-8, so it must be
+  // widened before decoding or every non-ASCII table name and note is mangled.
+  const binary = atob((node.textContent ?? "").trim());
+  const bytes = Uint8Array.from(binary, (character) => character.charCodeAt(0));
+  return JSON.parse(new TextDecoder().decode(bytes)) as ExportPayload;
+}