re: the remaining mis-decodes share one attractor, not pairwise confusion

Tested the tempting explanation for the last 51 -- that _l/_dead variants share
their base's vertex and index counts, making them mutually confusable and
adjacent so locality cannot help. It is FALSE: 2714 variant/base pairs across
every container, and exactly zero share identical counts.

What is actually happening is better news. e010_bdy_01_l is 171 verts / 90 tris
and NO other resource in its container shares those counts, yet in Stage_S02 and
S26 it decodes to 1600x2100x4800 -- the same bounds e303_wep_01 (172/110)
produced before the fix. Differently-shaped resources land on the same place, so
the attractor is a region of round axis-aligned box data that validates for many
(vtx, idx) shapes at once, not "another mesh with my shape".

That also explains why the neighbourhood fix helped so broadly: it steers
resources away from one strong attractor rather than resolving many pairwise
confusions.

Candidate next step recorded with its risk: de-prefer candidates whose sampled
positions are all multiples of 50 with a large span. It must be a TIEBREAK
between validating candidates rather than a rejection -- an earlier sweep for
that signature also flagged legitimate e_rou_* composite proxies -- and it needs
the same gate (decoded must not fall from 5480).

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

docs/re/structures/xbg7-mesh.md

@@ -426,12 +426,36 @@ now collected regardless of the filter, but only the asked-for ones and their ±
 neighbours are decoded in pass 1, so a filtered decode stays proportional to what
 was asked for.
 
-**51 remain**, and they cluster: `_l` (LOD) and `_dead` variants —
-`e001_l`, `e010_bdy_01_l`, `e011_bdy_01_l`, `e016_l`, `e104_bdy_05_l`,
-`e106_eng_02_l`, `e501_01_l`, `_rou_f301_base_dead`, `_rou_f302_base_dead`,
-`e303_base_dead`. 🟡 A plausible reading is that a variant shares its base's
-vertex and index counts, so the two are mutually confusable and the neighbourhood
-cannot separate them — untested. The ignored test
+**51 remain**, and they cluster in `_l` (LOD) and `_dead` variants — `e001_l`,
+`e010_bdy_01_l`, `e011_bdy_01_l`, `e016_l`, `e104_bdy_05_l`, `e106_eng_02_l`,
+`e501_01_l`, `_rou_f301_base_dead`, `_rou_f302_base_dead`, `e303_base_dead`.
+
+**A tempting explanation, tested and false.** The obvious reading is that a
+variant shares its base's vertex and index counts, so the two are mutually
+confusable *and* adjacent, defeating locality. Checked across every container:
+**2 714 variant/base pairs, and exactly zero share identical counts.**
+
+**What is actually happening: one region is a universal false positive.**
+`e010_bdy_01_l` is 171 verts / 90 tris and **no other resource in its container
+shares those counts** — yet in `Stage_S02` and `S26` it decodes to
+**1600 × 2100 × 4800**, the *same* bounds `e303_wep_01` (172 verts / 110 tris)
+produced before the fix. Differently-shaped resources are landing on the same
+place. So the attractor is not "another mesh with my shape" but a region of
+**round, axis-aligned box data** that validates for many different `(vtx, idx)`
+shapes at once — every index lands in range and the triangles are coherent boxes.
+
+That also explains why the neighbourhood fix helped so broadly: it steers
+resources away from a single strong attractor rather than resolving many
+pairwise confusions.
+
+🟡 **Candidate next step, with its risk stated:** reject (or de-prefer) a
+candidate whose sampled positions are *all* multiples of 50 with a large span —
+the attractor's signature. The risk is real: an earlier sweep for exactly that
+signature also flagged legitimate `e_rou_*` composite proxies, so it must be a
+**tiebreak between validating candidates**, never an outright rejection, and it
+needs the same before/after gate (decoded must not fall from 5 480).
+
+The ignored test
 [`mesh_consistency_disc.rs`](../../crates/sylpheed-formats/tests/mesh_consistency_disc.rs)
 still asserts the target state and now records 63 rather than 125; the remaining
 cases are where the neighbourhood is itself wrong or absent.