tools: Export- und Eingangsordner im Backup-Ziel - Überschneidungsregel nur noch auf <ziel>/git und den eigenen Maschinenordner, Laufzeitprüfung auf Vorfahren in upload collect und export run (#216); 10.1.0-beta.16

Files changed:
- CHANGES.md
- VERSION
- docs/how-to/back-up-to-a-synced-folder.md
- docs/how-to/collect-from-a-synced-folder.md
- docs/how-to/export-to-a-synced-folder.md
- docs/reference/commands/exports.md
- docs/reference/commands/raw-material-and-uploads.md
- docs/reference/configuration.md
- tools/CONTRACT.md
- tools/chemenu/backup.py
- tools/chemenu/collect.py
- tools/chemenu/commands/export_cmd.py
- tools/chemenu/commands/upload_cmd.py
- tools/chemenu/config_shapes.py
- tools/chemenu/page_export.py
- tools/chemenu/tests/test_collect.py
- tools/chemenu/tests/test_export_run.py
- tools/chemenu/upload.py

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

docs/reference/commands/exports.md

@@ -113,7 +113,7 @@ tools/wikitool export run work-notes
 - Every Markdown file starts with a frontmatter block whose `wikitool_export` line says `kind=pages instance=<origin URL without userinfo, or local> commit=<newest commit touching this page>`, followed by `title`, `type`, `summary`, `modified` where the page has them (`frontmatter: summary`, the default; `minimal` keeps only the marker, `full` the whole frontmatter), then the page text. A file keeps its path below `kb/`. A wikilink to an exported page becomes a relative Markdown link (`links: relative`, the default) or plain text (`links: text`); a link to a page that is not exported is always plain text. Footnote markers stay; code is never rewritten. LF endings, no timestamp: the same pages give the same bytes, and a commit that touches one page rewrites that page's file alone - plus any file whose links change because a page entered or left the selection. The manifest's `commit` is the newest commit touching any selected page; all of them come from one `git log`, however many pages are selected.
 - Handler `command`: the Markdown is rendered into a staging directory, the program of `export.commands` runs with no shell, stdin closed and a timeout of 300 s, and receives the Markdown directory and an empty output directory as its last two arguments. On exit 0 the regular files in the output directory (recursively) become the target's content; any other end leaves the target unchanged and prints the end of its stderr. The staging directory is always removed.
 - The folder is only ever touched by what it holds in its manifest, `.wikitool-export.json`: the files an earlier run wrote, each with its sha256. A run removes only manifest files that are no longer exported (and folders it created, once empty), rewrites a manifest file that is missing, leaves every other file byte for byte as it was, and writes nothing - not even a modification time - for a file that did not change. A run that changes nothing writes nothing at all.
-- Refuses a target, before writing anything into it: a non-empty folder with no manifest (it is somebody's, not an export), a manifest file that was changed in the folder since the last run (naming it), a foreign file where an exported one belongs, an empty selection (it would delete the earlier export), an unknown field in a predicate. A missing folder is created.
+- Refuses a target, before writing anything into it: a non-empty folder with no manifest (it is somebody's, not an export), a folder that holds or lies in backup data (a `.chemenu-backup.json` - any machine's, also one this checkout does not know - or a bare git repository), a manifest file that was changed in the folder since the last run (naming it), a foreign file where an exported one belongs, an empty selection (it would delete the earlier export), an unknown field in a predicate. A missing folder is created.
 - Refuses everything, before any target: uncommitted changes in `kb/` or `types/` (untracked files included), no git checkout, a page under `kb/` with unreadable frontmatter, an unknown target name, a broken `export` section.
 - Output per target: `new` (with the page titles), `changed`, `removed`, the count `unchanged`, or `failed` with the reason. A page that newly enters a selection is reported as new, not gated. Exit 0 when every target ran; exit 1 when any failed - the others were still served.
 - A target with `after_publish: true` is also refreshed by every `publish` that committed, `--no-push` included; a failure there is a warning, the commit stands, and this command is the repeat.