re(xbg7): the [index][vertex] layout is runtime-verified, and the indices= mystery was batching

The decoder's central unstated assumption — a block's index buffer sits
immediately before its vertex buffer (`vb - idx_count*2 - pad`, pad <= 3) — was
also the prime suspect for the residual anchor misses, since a capture-proven
`e106_eng_02_l` block was rejected outright. Measured it instead of assuming:

- extended the F10 ship capture to log each draw's index buffer (base, count,
  min/max index) and to key its de-dup on the index range, so every draw batch
  is recorded rather than only the first;
- `examples/capture_ib_truth.rs` places each drawn buffer in the container by its
  dumped positions and scores the capture against our decode.

Stage_S02, 42 drawn buffers placed: our idx_count == the sum of the draw's index
batches for 42/42, the batch union covers the vertex pool exactly for 42/42, and
all 30 single-block cases sit at pad <= 3 (20 at pad 0, 10 at pad 2). The other
12 are grouped pools, where one index pool serves the whole group. So the layout
holds, the decoded index count is exact, and eng_02_l died on the connectivity
gate (since replaced by the winding gate) — not on index location. The shipped
exact-coverage rule is independently confirmed.

The recorded "capture indices=21 vs our 246" disagreement was an artefact of the
old de-dup key: 21 was the first of two batches, 21 + 225 = 246. Any conclusion
from a pre-2026-08-13 capture's `indices=` or `vbase - ibase` is about one batch,
not about the block.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NptfmpjdpNCKEez6d2xvA9

docs/re/INDEX.md

@@ -19,7 +19,7 @@ Promote to a prose `structures/…md` file when a format needs behavioural notes
 | LSTA sprite list | ✅ | `sylpheed-formats/src/lsta.rs` | A display list of inline elements: **T8aD sprites and `PRMD` primitives**. The `count` at `0x04` is **exact and counts both** — `count == T8aD + PRMD` for **64/64** lists on the disc, which retires the old "a few entries disagree" note (it compared sprites against a total including primitives). **All 1 281 sprite frames decode** after the T8aD rectangle-list fix |
 | IXUD subtitle | 🟡/✅ | `sylpheed-formats/src/ixud.rs` + [movie link](movie-subtitle-link.md) | timed cues. **The movie↔subtitle↔voice link is solved — statically**, from the movie config record in `tables.pak` (schema `0x067025b9`), not from the running game as this row previously assumed: [101 movies mapped](captures/movie-subtitle-voice-map.csv), 94 with subtitles, 83 with voice, 21 with a telop overlay. 93 of 94 subtitle refs resolve in the language paks; **`SUBTITLE_S12B.tbl` is missing from all six languages** — a dangling reference on the disc. Naming is `SUBTITLE_<base>.tbl` / `VOICE_<base>` with six documented exceptions. The record's ~104 **script ids** are ❔ — positional pairing drifts by three because the IDXD pool dedupes repeated values |
 | Fonts (ttf/otf/ttc) | ✅ | `sylpheed-formats/src/font.rs` | standard OpenType, parsed via ttf-parser |
-| XBG7 mesh | ✅/🟡 | `sylpheed-formats/src/mesh.rs` + `tests/mesh_disc.rs` ([xbg7](structures/xbg7-mesh.md)) | **6 294 resources, 6 209 decode (98.7 %), 82 searched-and-missed** (2026-08-12, up from 5 480 / 87.1 %). Five evidence-driven fixes got there: **distinct anchor assignment** (no two resources may claim one buffer — proved by a capture showing the container holds both mirrored `e106` hull halves), the connectivity cap replaced by a **winding-consistency gate at 0.70**, **structural requirements on pre-pivot sub-meshes** (index range, then exact pool coverage), and **filtering after the assignment** so a subset query cannot differ from the full decode. Validated against a runtime capture that names the file offset of every buffer the engine drew: **46/46 drawn buffers claimed, 45 anchored exactly**. **No real mesh now decodes differently in different containers** — all 89 remaining cross-container disagreements are interchangeable 24-vertex bounding boxes, which no anchoring rule can pin (monotone order re-tested and refuted). Remaining misses attribute to the degeneracy/extent gate (42), winding (31) and coverage (9); the first was probed and its "obvious" fix refuted. Every decoded sub-mesh covers its own vertex pool |
+| XBG7 mesh | ✅/🟡 | `sylpheed-formats/src/mesh.rs` + `tests/mesh_disc.rs` ([xbg7](structures/xbg7-mesh.md)) | **6 294 resources, 6 209 decode (98.7 %), 82 searched-and-missed** (2026-08-12, up from 5 480 / 87.1 %). Five evidence-driven fixes got there: **distinct anchor assignment** (no two resources may claim one buffer — proved by a capture showing the container holds both mirrored `e106` hull halves), the connectivity cap replaced by a **winding-consistency gate at 0.70**, **structural requirements on pre-pivot sub-meshes** (index range, then exact pool coverage), and **filtering after the assignment** so a subset query cannot differ from the full decode. Validated against a runtime capture that names the file offset of every buffer the engine drew: **46/46 drawn buffers claimed, 45 anchored exactly**. **No real mesh now decodes differently in different containers** — all 89 remaining cross-container disagreements are interchangeable 24-vertex bounding boxes, which no anchoring rule can pin (monotone order re-tested and refuted). Remaining misses attribute to the degeneracy/extent gate (42), winding (31) and coverage (9); the first was probed and its "obvious" fix refuted. Every decoded sub-mesh covers its own vertex pool. **The `[index buffer][vertex buffer]` layout is now runtime-verified** (2026-08-13): with the F10 capture extended to log each draw's index buffer, all **42** drawn `Stage_S02` buffers match our decoded index count exactly, all 42 have their index union cover the pool exactly, and the 30 single-block cases all sit at `pad ≤ 3` — so `e106_eng_02_l`'s old rejection was the connectivity gate, not a misplaced index buffer. The `indices=` mystery was the capture keeping only the **first of several index batches** per buffer |
 | Capital-ship part placement | ✅ | `sylpheed-formats/src/ship.rs` (static) + [runtime capture](ship-placement-runtime-capture.md) | Placement is **sound** (hull static-exact against the `e106` capture; cross-id mounting genuinely narrow, 2 pairs across 335 ships). The XBG7 mis-decode this row used to blame for "ships assemble wrong" — a shared turret ~100× too large in some containers — is **fixed** (2026-08-12, the exact-coverage requirement): `e303_wep_01` now decodes 49×23×42 everywhere and places at ±179 on the `e106` hull, and no real mesh disagrees across containers. A composite-node audit confirmed the assembler itself never applied a bad scale (all nodes scale 1.0, orthonormal). Still open: `static_assembly_matches_runtime_capture` walks capture parts only, so **extra** static placements cannot fail it |
 | Weapon fields defaulted on disc | ✅ | [runtime struct](structures/weapon-struct-runtime.md) · [DATA SHEET route](weapon-datasheet-runtime.md) | **Solved.** Canary maps guest RAM into `/dev/shm`, so the parsed `Weapon`/`Shell` objects are readable live; their layout is solved against disc ground truth (zero contradictions over 100+ records). All 126 weapons, exact numbers, no story progress needed — [4 393 values](captures/weapon-runtime-fields.csv) the disc does not carry. Supersedes the letter-bucket limit of the DATA SHEET route, which now serves as the independent cross-check |
 | Unit (craft/vessel) fields defaulted on disc | ✅/🟡 | [runtime struct](structures/unit-struct-runtime.md) | The parsed `unit\UN_*.tbl` definition object, vtable `0x820af844`, ≥`0x380` bytes, one per unit — **discovered, not assumed** (`unit_discover.py`), and distinguished from the spawned-entity class `0x820af030` by being one-per-ID and byte-constant within a run. Across runs only pointer words move — `--crosscheck` proves **no reported field offset is run-dependent** (two words, `+0x2c8`/`+0x2d0`, are stage-dependent and remain unidentified). 27 fields ✅ (21 units, 7 runs); the `Maneuver` block is **schema declaration order, 4 bytes/field, base `0x9c` with a two-slot gap after `AA_Roll_Min`** (29 anchors, 0 conflicts), which also pins 5 fields *no* disc record ever values. Angles are **radians at runtime, degrees on disc**. **Re-derived independently 2026-08-13 from the loader's own key strings** (`sub_82341A20`; the field name for each store is a string in the image): **159 fields**, agreeing with this solver on **25 of 25 shared offsets**, verified at **406 values matching the disc and 0 disagreeing** over 11 live objects spanning UNIT and VESSEL — landed as `data/unit_definition_layout.txt` + `sylpheed_formats::unit_layout` + a no-emulator test, with **121 defaulted fields** read out ([live-unit-definitions](live-unit-definitions.md)). Unlike weapons, unit definitions are instantiated **per stage**, so coverage (21/110) grows by visiting missions — but a defaulted field is **not** a global constant: `Size_Y` provably inherits `Size_X` (7 independent units, 6 distinct values), and three more sibling rules are recorded ❔, recovering 65 values in units never visited — [values](captures/unit-runtime-fields.csv) |