re: INDEX row for the nameless IDXD field keys

Records the census, the 504-entries-not-504-names correction, and the null
result on cracking with the arithmetic that makes it a null result rather
than a shrug.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE

docs/re/INDEX.md

@@ -13,6 +13,7 @@ Promote to a prose `structures/…md` file when a format needs behavioural notes
 | IPFB `.pak` archive | ✅ | `sylpheed-formats/src/pak.rs` + `tests/pak_idxd_disc.rs` | header + 12-byte TOC, Z1/zlib payloads |
 | name-hash (TOC keys) | ✅ | `sylpheed-formats/src/hash.rs` | Barrett-reduction hash; recovers original paths |
 | IDXD object/table | ✅ | `sylpheed-formats/src/idxd.rs` | self-describing; ship/weapon stats verified vs known values |
+| IDXD nameless field keys | ✅/❌ | [idxd-unnamed-keys](structures/idxd-unnamed-keys.md) + [`tools/re-capture/idxd_unnamed_keys.py`](../../tools/re-capture/idxd_unnamed_keys.py) | Census of every field entry whose `name_off` is `0xFFFFFFFF`, disc-wide: **7 750 objects, 2 757 039 field entries, 0 parse failures**, `tag_hash` reproducing **1 271 462/1 271 462** named keys. **7 094 distinct keys are never named — and 7 052 of them are not hashes at all**, but author-assigned element ids (equal to the field's own index in 1 404 924 of 1 485 577 cases; `tag_hash("BGM_001")` is `0xC662435B` while the key valued `BGM_001.slb` is `0x000003E9`). ⚠️ **The "504 hash-keyed nameless fields" figure is 504 ENTRIES, not 504 names** — 42 distinct keys × 6 language copies × 2 records. All 42 are **ISL script-symbol hashes** in `<lang>\script\ID.tbl` (GP_READY_ROOM.pak), the link map built by `PrepareScript`'s "isl script prescanning"; 41 of 42 appear as little-endian call targets inside the `.isb` bytecode, forming a coherent launcher/helper call graph. The hash's own algebra pins the **trailing digits of 30 of the 42 names** (deltas of exactly `+0x01000001` across `stage01..09`, `stage10..16`, `challenge01..06`; `+0x01010000` across `tutorial0101..0601`). ❌ **No name was cracked, and the negative is quantified**: seven attacks up to a 3.5×10⁸ composition space found nothing above the noise floor; exhaustive preimage search recovers `"Stage01"` from its own hash but returns nothing for the real targets at ≤6 characters, and at 7 characters one target already has **1 176** preimages — a 24-bit modulus cannot name an 8+ character identifier uniquely |
 | XPR2 texture + cubemap | 🟡/✅ | `sylpheed-formats/src/texture.rs` + [colour check](xpr2-colour-check.md) | de-tile + A8R8G8B8 and DXT1. **Channel order ✅ confirmed against the running game**: the Delta Saber's decoded atlas is orange-dominant (median saturated hue 23.3°, *zero* cool pixels) and the game renders the same hull at 9.3° — a red↔blue swap would sit at ≈200°. Exact fidelity (gamma/sRGB curve, premultiplied alpha, per-channel scale) is 🟡 untested, since a hue comparison cannot see it; cubemap face ordering ❔ |
 | T8aD 2D texture | ✅ | `sylpheed-formats/src/t8ad.rs` | **100 % of the disc decodes** (19 216/19 216, measured). The "~15 % deferred variants" were a wrong model, not a variant: a surface is a list of **arbitrary sub-rectangles**, each with a 16-byte header of `dst X, dst Y, width, height`, not a 256×256 grid — `0x1c` is the **rectangle count**. Uncovered area stays transparent. **Colours ✅ CONFIRMED** ([k8888](structures/texture-color-k8888.md)) |
 | RATC bundle | ✅ | `sylpheed-formats/src/ratc.rs` | child listing confirmed. **"One level deep" is not a limitation — there is nothing deeper**: 2 859 bundles hold 18 002 children at depth 1 and **0 at depth 2**, with no parse failures. Nested RATC blobs are **leaf records that reference siblings by name** (`opt `, the sprite name): 3 311 leaves, all embedding sibling names, **10 144 of 10 148 references resolve**. The 4 that do not are one dangling asset — `pmbase.rat` → `pmbase.t32` in `GP_STAGE_CLEAR.pak`'s four language builds, and `pmbase.t32` is **on the disc nowhere** |