re: eng_02_l's real block is adjacent -- the connectivity heuristic rejects it

debug_find_index_buffer scans the container for an index buffer that validates
against a capture-proven vertex buffer. For eng_02_l nothing validates with the
connectivity test on; with it off the nearest hit is exact pad-0 adjacency
(vb-ib = 144 = 72*2). The block's mean_edge/diag is 0.417 against a 0.28 cap --
the documented false positive for coarse LODs, now caught with ground truth.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/sylpheed-formats/examples/find_ib.rs

@@ -0,0 +1,27 @@
+//! Where could a resource's index buffer be, given the vertex buffer a runtime
+//! capture proves the engine drew from? Tests the anchor scan's adjacency
+//! assumption against ground truth.
+use sylpheed_formats::mesh::{debug_find_index_buffer, debug_resource_params};
+fn main() {
+    let a: Vec<String> = std::env::args().collect();
+    let bytes = std::fs::read(&a[1]).unwrap();
+    for pair in a[2..].iter() {
+        let (name, off) = pair.split_once('@').unwrap();
+        let vb = usize::from_str_radix(off.trim_start_matches("0x"), 16).unwrap();
+        let params = debug_resource_params(&bytes, name);
+        let markers = params.as_ref().map(|(m, _)| m.clone()).unwrap_or_default();
+        println!("{name} @ 0x{vb:x}  markers={markers:?}");
+        let hits = debug_find_index_buffer(&bytes, name, vb);
+        if hits.is_empty() {
+            println!("   no index buffer anywhere in the container validates this block");
+        }
+        let mut hits = hits;
+        hits.sort_by_key(|(_, d)| d.abs());
+        for (ib, d) in hits.iter().take(8) {
+            println!("   ib 0x{ib:x}  vb-ib = {d} bytes");
+        }
+        if hits.len() > 8 {
+            println!("   … {} total", hits.len());
+        }
+    }
+}