Version history: new document_versions table (migration 0003) holding
full-body snapshots that cascade with the doc. Throttled auto-snapshots
on save (>=3min apart, max 40/doc, pruned), explicit manual restore
points, and a pre_restore safety copy taken before each restore so
restoring is itself undoable. Endpoints under /api/docs/:id/versions,
all owner-scoped. Empties and bare renames never snapshot.
Export: pure-Go Tiptap-JSON -> Markdown / HTML / plain-text / docx
(no cgo/pandoc, single-binary intact), CJK-safe with RFC 5987
filenames. docx is a hand-built OOXML zip. PDF is handled client-side
via the browser print dialog + an @media print stylesheet so CJK
renders with the reader's own fonts.
Frontend: ExportMenu (downloads + Print/PDF) and HistoryPanel
(snapshot list, preview, restore) wired into the title row; bilingual
zh-first to match chrome. Restore remounts the editor via editorEpoch.
Stop saving empty docs: blank Untitled drafts now reuse-on-create and
self-discard when navigated away from (refs avoid stale closures).
Tests: versions_test.go, export_test.go (incl. valid-zip docx).
go build/vet/test, tsc, vite build all clean; live end-to-end smoke
verified snapshot/throttle/restore/export.
Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd
