docs: bring INDEX and BACKLOG up to the measured state

INDEX's XBG7 row still said 5480 decode (87.1%) and 125 of 681 shared resources
failing; it is now 6209 of 6294 (98.7%) with zero real meshes disagreeing across
containers and 46/46 capture-verified drawn buffers. The capital-ship row blamed
an XBG7 mis-decode for the user-reported assembly bug -- that mis-decode (a shared
turret ~100x too large) is fixed, so the BACKLOG entry is marked resolved at the
format layer, keeping the viewer-side pointers and the note that no metric caught
it: it took rendering the ship and looking.

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

docs/re/BACKLOG.md

@@ -8,8 +8,30 @@ unknown, what evidence exists, and what the first step would be. Move an item in
 
 ## Capital ships assemble wrong in the viewer
 
-**Reported:** 2026-07-30, by the user. **Status:** 🔎 **diagnosed 2026-08-10 — the
-format layer is exonerated.** Runtime captures of three classes (`f105`, `e105`,
+**Reported:** 2026-07-30, by the user. **Status:** ✅ **format-side cause found and
+fixed 2026-08-12** — see below for the 2026-08-10 diagnosis this supersedes.
+
+The remaining format-side defect this entry pointed at (a shared turret decoding
+~100× too large in some containers) was real and is gone. `e303_wep_01` decoded
+as a 1600×2100×4800 block in `Stage_S02`, swallowing the `e106` hull; requiring an
+index buffer to cover its vertex pool **exactly** moved it to the block every
+other container agrees on, and it now decodes 49×23×42 everywhere and places at
+±179 on the hull. The same fix repaired `e106_bdy_03` (a 600×1600×998 slab) and
+moved 29 anchors disc-wide, 22 of which had been carrying **another resource's
+geometry under their own name**. See
+[`structures/xbg7-mesh.md`](structures/xbg7-mesh.md).
+
+Two things are worth carrying forward rather than closing:
+- the assembler was **audited and exonerated** — every composite node carries
+  scale 1.0 and an orthonormal matrix, so nothing on that side inflates a part;
+- **no metric caught this.** Coverage, cross-container consistency, the capture
+  oracle and the twin invariant were all green while a 1 600-unit slab sat through
+  the ship. It was found by *rendering the ship and looking at it*, and the
+  numeric screens written afterwards to automate that check both failed.
+
+The 2026-08-10 diagnosis follows, and its viewer-side pointers still stand.
+
+**Status (2026-08-10):** 🔎 **the format layer is exonerated.** Runtime captures of three classes (`f105`, `e105`,
 `e106`) at controlled range reproduce `assemble_ship` to ≤0.43 units in translation
 and to 0.000 in rotation for every part that does not move; see
 [`ship-placement-capture-generalisation.md`](ship-placement-capture-generalisation.md)