export obsidian: never prunes notes for removed nodes, so re-export merges old and new graphs #1896

Version: 0.9.15

graphify export obsidian writes notes for the current graph's nodes and refuses to overwrite files it does not recognise as its own — but it never deletes notes for nodes that no longer exist. Re-exporting over an existing vault therefore merges the old and new graphs into one pile.

Repro

1. Extract, then export obsidian (graph A → vault holds A's notes).
2. Change the corpus, or re-extract at a different mode, so the graph changes materially.
3. export obsidian again into the same directory.

Actual

The vault holds old ∪ new. Observed after a full rebuild: 276 notes, of which 126 were orphans from the previous graph — the new graph had 187 nodes + 29 communities, i.e. 216 legitimate notes. Exit code 0, and no warning about the orphans. (It did warn that it skipped one pre-existing foreign file rather than overwrite it, so the exporter clearly already distinguishes its own files from other people's.)

Expected

Prune the notes the exporter itself previously wrote for nodes that are now absent — the ownership signal needed to do this safely already exists, given the overwrite protection. Failing that, warn with an orphan count so the merge isn't silent.

Workaround today is rm -rf on the vault directory before every export.