Symptom: open a non-UTM drawing, most lines/polylines/hatches/etc.
vanish — only ~5% of indexed entities reachable from a huge query
(walking the nodes flat showed all 2975 items present, but recursing
through `node.children` from root reached only 161).
Root cause: when straddler items piled up at an INTERNAL node and the
count exceeded LEAF_CAPACITY, `insert()` re-invoked `split()` on that
node. `split()` allocates four fresh children and assigns them to
`node.children = Some([...])` — overwriting the existing children
pointer and orphaning the entire previous subtree (the descendant
nodes still hold their items; nothing reaches them).
Splitting an internal node is futile anyway: straddlers don't fit
smaller children either. Fix: gate the split on
`children.is_none()` so only leaves split. Internal nodes accumulate
straddlers as a linear-scan list — slower per-query for big strad-
dler counts, but correct.
Adds a regression test (`many_straddlers_dont_orphan_subtree`) that
floods an internal node with straddlers and verifies a huge query
still returns every inserted handle.
Bonus: `examples/dump_index_stats.rs` — standalone tool that loads a
DWG/DXF and dumps per-type counts (indexed / unbounded / top-level /
block-internal) plus a sample of bboxes. Useful for future bug
triage; built and ran cleanly against the file that exposed this.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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