re: n206 was fixed after all -- the audit was classifying by geometry, not buffer

debug_grouped_report (why_rejected) shows n206_02's alternative pool is ACCEPTED
at pad 0 under production gates and is in the candidate list -- and the decoder
does take it: n206_02 now anchors at 0x342d984. The 'still collapsed' reading
came from the audit comparing decoded geometry, and that offset holds a direct
(unmirrored) copy, so a separated pair still looked identical. The audit now
requires a SHARED BUFFER to call it a collapse: disc-wide 18 exact mirrors, 16
related, 0 collapses, 0 unrelated -- and the regression test drops its exception.

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

crates/sylpheed-formats/tests/mesh_consistency_disc.rs

@@ -108,10 +108,9 @@ fn shared_resources_decode_identically_in_every_container() {
 /// A runtime capture showed the container stores both halves of the `e106` hull
 /// as separate X-reflected buffers, so a `…_01`/`…_02` pair of equal vertex
 /// count should come out mirrored (or related by another axis / vertex order) —
-/// never identical, which is the collapse distinct assignment fixes. Disc-wide
-/// this holds for every such pair except `n206`, whose twins are grouped-pool
-/// resources (4 sub-meshes) and so are excluded from distinct assignment; that
-/// one is the remaining known case, asserted explicitly so it cannot grow.
+/// never identical, which is the collapse distinct assignment fixes. Since that
+/// fix reached grouped pools too, this holds for **every** twin pair on the disc
+/// — including `n206`, which was the last exception.
 #[test]
 fn twin_pairs_do_not_share_a_buffer() {
     let Some(root) = disc_root() else {
@@ -141,6 +140,5 @@ fn twin_pairs_do_not_share_a_buffer() {
             }
         }
     }
-    collapsed.retain(|c| !c.starts_with("n206_01"));
     assert!(collapsed.is_empty(), "twin pairs sharing one buffer: {collapsed:?}");
 }