export, import: an export that pours back into a workspace whole

An export used to lose what plain files cannot carry: dates, names as
typed, the boards. It now writes .workspace.json beside the tree (format
1), and an import that finds one restores them. The markdown stays
plain, so the archive still reads without the application.

POST /api/import (:import! / in the UI) imports at the root: each
top-level directory becomes a space, or merges into the space already
there by that name, with its board and cards and the diary role. With a
manifest, media/ comes back as embedded files rather than a folder, a
file whose name ends in .md stays a file, and empty folders come back.

Export claims every path in one set, folders, then documents, then
files, so a file named notes.md beside a document notes no longer makes
a duplicate entry that failed the whole zip. Links to folders are
rewritten like links to documents, in one regex pass per kind instead
of a replace per file and document. A sealed file that will not open
now fails the export instead of being left out silently. The temporary
zip is made in the data directory, not in /tmp.

README.md

@@ -158,10 +158,13 @@ it is removed again on the way out, so abandoned starts do not pile up. If a tab
 says so — `:e!` throws it away, the way vim handles a swap file.
 
 `:export` downloads the open document as markdown. `:export!` downloads the
-whole workspace as a zip: the tree as real directories, one markdown file per
-document, every file in the tree where it sits and every other embedded file in
-`media/`, under their real names, and relative links between them, so the
-archive reads in any markdown viewer without this application.
+whole workspace as a zip: the tree as real directories, empty folders too, one
+markdown file per document, every file in the tree where it sits and every
+other embedded file in `media/`, under their real names, and relative links
+between documents, folders and files, so the archive reads in any markdown
+viewer without this application. What plain files have no place for — when
+each entry was written, names as they were typed, which space is the diary,
+every board with its cards — goes into one `.workspace.json` beside them.
 
 The diary is the diary by role, not by name: rename it and the reminder and
 the agenda still know which space it is, and it cannot be deleted — empty it
@@ -237,8 +240,12 @@ Proton cannot read either; only the vault password can read the sealed one.
 had inside, and the tree is rebuilt on the other side: directories become
 folders, `.md` and `.markdown` files become documents (titled by their first
 heading), anything else becomes a file in the tree. `:import!` does the same with
-a zip, which is the shape `:export!` writes, so a workspace can be poured back
-into another one.
+a zip, which is the shape `:export!` writes. `:import! /` pours an `:export!`
+back in at the root: each directory becomes a space again — or goes into the
+space already there by that name — and with `.workspace.json` beside it the
+dates, names, boards and cards come back as they were, embedded files go back
+to being embedded rather than a `media` folder, and a file that happened to end
+in `.md` stays a file.
 
 Links between the imported files are rewritten as they land: a link to a
 markdown file becomes the document's address, a link to an image becomes its
@@ -433,9 +440,10 @@ Everything except the two share routes requires the session cookie.
 | `POST` | `/api/cards/{id}/move` | to another list and place in it |
 | `POST` | `/api/nodes/{id}/move` | reparent, and place among the new siblings |
 | `POST` | `/api/nodes/{id}/import` | import a folder or zip (multipart) under this node |
+| `POST` | `/api/import` | import an export at the root: directories become spaces |
 | `GET` | `/api/resolve?path=` | the node behind a slug path, `work/notes/monday` |
 | `POST`/`DELETE` | `/api/nodes/{id}/share` | mint or rotate / revoke a share link |
-| `GET` | `/api/export` | every document and file, as a zip |
+| `GET` | `/api/export` | the whole workspace, boards and dates included, as a zip |
 | `GET`/`POST` | `/api/backup` | Proton Drive mirror: status / run now |
 | `GET`/`POST` | `/api/media` | list / upload (multipart) |
 | `GET`/`DELETE` | `/api/media/{id}` | serve / delete a file |