fix(D176a): phase-fold sky texcoords to kill the horizon streak (Defect 1)

Cloud tile is s_skywaterimages[0] = 64x64 IA8, G_TX_WRAP -> it tiles.
GE's screen-space textured-quad idiom is tc = width<<5 (glass2.c:678), so
skyPortRenderPoly's *32.0f scale was correct; the bug was (s16) overflow on
the +/-20k-texel horizon S/T (unk20/unk24 are texel coords, not fractions).

Fix: fold every vertex of one primitive by the same multiple of the 64-texel
tile period before scaling. Inter-vertex deltas (hence the interpolated
cloud texture) are preserved; magnitudes stay in s16 range. Exact for any
triangle whose S/T span is < ~1000 texels -- everything except tris
straddling the horizon line, which are Defect 2 (adaptive tessellation).

sky.c #ifdef PORT only; N64 path unchanged. Builds clean; bunker1 + statue
verify PASS, no crash. UNVERIFIED VISUALLY -- owed: one -level_22 screenshot
(D176a-SKY-NOTES.md 'Verification ask').

Also: rebased onto main (porting-notes.md conflict resolved).

docs/dev/GRAPHICS-BACKLOG.md

@@ -21,7 +21,7 @@ once the game is playable start-to-finish without crashes.
 | **D172** | Bullet-impact / blood particle spray renders magenta or cyan instead of dark red (visible on guards hit at close range on Silo). | **Root-cause candidate found, static research done** (`docs/dev/D172-PARTICLE-COLOR-RESEARCH.md`). Particles get CC/tile state from 15 ROM records replayed via `gSPDisplayList` (`explosion.c:894`); each record contains an opcode **0xB9** that fast3d does not handle → the D146 unknown-opcode guard kills the sub-DL before the record's `G_SETCOMBINE`+`G_SETTIMG` apply → particles draw with stale state = magenta/cyan. SETCOMBINE decode itself verified correct. Verify in-game: watch console for `D146: unknown GBI opcode 0xb9` while shooting (rate-limited to 20). Fix: decode 0xB9 semantics (ginit.s missing from repo — trace gmain.s 0x80–0xBF group or infer from data) + implement in fast3d. |
 | **D178** | Objectives not listed correctly on the pre-mission briefing screen (the mission overview shown before starting a level). | **M-36 triage: the objective lines are BLANK, not wrong.** `GE_STARTMENU=10` Dam briefing renders the header fine ("OHMSS / Agent: James Bond / Mission 1: Arkangelsk / Part i: Dam / PRIMARY OBJECTIVES:") then just the bullet "a." with no text and no b/c/d. → **D143/D151 blank-text family** (`langGet()` → NULL → silent blank), *not* a propDef walk / difficulty decode. **Family B** in `docs/dev/M-36-TRIAGE.md` — find which lang bank the front-end briefing flow fails to load. Re-confirm the exact shape in a *real* briefing (the `GE_STARTMENU` boot skips real save state). Close relatives: D151 (watch objective text blank — type-35/23 `text` slot u16→u32 fix, M-28; interactive re-verify was still pending), D143 (briefing/objective text blank via `langGet` NULL), D157 (objective difficulty byte offset — could make difficulty-gated objectives appear/disappear wrongly). The pre-start briefing is a *different surface* from the in-level watch, so D151's fix may not cover it. **Next:** ask user which level + what exactly shows vs expected; compare against `docs/dev/LEVEL-OBJECTIVES.md` (regenerated post-D157); if lines are blank → D143/D151 family (`langGet` NULL guard = silent blank), if wrong objectives listed → propDef type-23 record walk / difficulty decode. |
 | **D175** | In-game stutter / brief hang during normal play — observed opening a door on Runway (mission 3, `-level_35`) and also on Surface. No backtrace captured (gdb attach missed the window; it self-recovered). | **Observed, not investigated** (user QA report). Matches known transient-hang classes rather than looking new: D155 (post-slow-load catch-up spiral — clamped), D156 (anim NaN loop — guarded, prints one-shot stderr diag if it fires), D134 (SP/DP task-done event swallowed — fixed M-22, Runway was an original victim), D147/D152 (audio `s_imLock` steal = ~2 s hiccup). Door-open specifically = new room first visible → one-off texture-import/frame spike (likely benign). **Next:** reproduce under `tools_pc/debug.ps1` with the box idle; check console for the D156 stderr diag; if it recurs, attach gdb mid-hang and pattern-match `bt` (import_texture = benign slow frame; model.c:3131 spin = D156; pthread_mutex_lock on s_imLock = D147/D152). |
-| **D176** | Surface exterior renders wrong (two co-located defects). **(a)** Sky is solid **black** — the skybox / sky gradient does not draw at all (reference: warm sunset cloud gradient). **(b)** The perimeter **tree-line backdrop renders as grey TV-static / comb interlacing** instead of snow-laden pines — the geometry is present and roughly the right silhouette but every tree texture is scrambled noise. Ground, tunnel and the dish/bunker building draw fine. | **Observed, screenshots committed** (M-35, user QA; `docs/img/bugs/d176-surface-exterior-our-build.png` vs `-reference.png`). Level is the shared Surface exterior — user reached it Dam→Surface on Agent so this is **Surface (i) `-level_36`** (confirm it also affects `-level_43`). **(a)** black sky: **M-36 partial (findings.md "D176(a)").** Env data is correct (`Sky.Clouds=1`, `CloudRGB=240,120,30`, `SkyImageId=0`); `skyRender` runs the cloud path and classifies corners correctly (switch case 12), but `skyRenderTri`/`skyRenderFull` emit nothing — not even the `env->RGB` fill shows. Not root-caused: next is probing `sub_GAME_7F097388` projected coords, verifying `skywaterimages[0]` resolves on PC (`image_bank.c` GIMG offset `0xFB4`), and a fast3d sky-tri trace. `GE_D176=1` probe shipped. **M-37: ROOT-CAUSED** — `skyRenderTri`/`skyRenderFull` build geometry *exclusively* as `G_RDPHALF_*` immediates, which `gfx_pc.cpp` deliberately no-ops (identical no-op in the PD port); fix = decode the RDPHALF tri-raster stream in fast3d (~1 session, genuine new code). **M-42: `-level_22` (Statue) confirmed a clean headless repro** — bare boot, frame ~360, upper half pure black; use it to verify the decoder. **M-47 + read-only consolidation:** Path B draft exists (`scratchpad/sky.patch`, `skyPortRenderPoly` PORT hook — geometry+texture reach GL, two unit defects open) and the full RDPHALF wire format is now decoded (S15.1 half-packing, 8-component perspective-interpolated vertex vectors); next session is mechanical per `docs/dev/D176a-SKY-NOTES.md`. `-level_36`/`-43` intro cams face down (not a sky test without `GE_INPUTSCRIPT`). **(b)** tree/rock static: **M-36 triage — NOT the D159 family.** `texSwapAltRowBytes` is a full `#ifdef PORT` no-op (`image.c:2199`), it cannot cause this. Real cause: `port/fast3d/gfx_pc.cpp` `import_texture_*` assume `line_size_bytes == full_image_line_size_bytes` (`SUPPORT_CHECK`; rgba16's is commented out *"trips ... with a garbage size"* `:658`) → non-PoT / sub-rect tiles get a flat linear read → diagonal row shear = grey static. **Family A** in `docs/dev/M-36-TRIAGE.md`. Fix: honour `line_size_bytes` as the real source pitch. Same defect as D182(2). |
+| **D176** | Surface exterior renders wrong (two co-located defects). **(a)** Sky is solid **black** — the skybox / sky gradient does not draw at all (reference: warm sunset cloud gradient). **(b)** The perimeter **tree-line backdrop renders as grey TV-static / comb interlacing** instead of snow-laden pines — the geometry is present and roughly the right silhouette but every tree texture is scrambled noise. Ground, tunnel and the dish/bunker building draw fine. | **Observed, screenshots committed** (M-35, user QA; `docs/img/bugs/d176-surface-exterior-our-build.png` vs `-reference.png`). Level is the shared Surface exterior — user reached it Dam→Surface on Agent so this is **Surface (i) `-level_36`** (confirm it also affects `-level_43`). **(a)** black sky: **M-36 partial (findings.md "D176(a)").** Env data is correct (`Sky.Clouds=1`, `CloudRGB=240,120,30`, `SkyImageId=0`); `skyRender` runs the cloud path and classifies corners correctly (switch case 12), but `skyRenderTri`/`skyRenderFull` emit nothing — not even the `env->RGB` fill shows. Not root-caused: next is probing `sub_GAME_7F097388` projected coords, verifying `skywaterimages[0]` resolves on PC (`image_bank.c` GIMG offset `0xFB4`), and a fast3d sky-tri trace. `GE_D176=1` probe shipped. **M-37: ROOT-CAUSED** — `skyRenderTri`/`skyRenderFull` build geometry *exclusively* as `G_RDPHALF_*` immediates, which `gfx_pc.cpp` deliberately no-ops (identical no-op in the PD port); fix = decode the RDPHALF tri-raster stream in fast3d (~1 session, genuine new code). **M-42: `-level_22` (Statue) confirmed a clean headless repro** — bare boot, frame ~360, upper half pure black; use it to verify the decoder. **M-47 + read-only consolidation:** Path B draft exists (`scratchpad/sky.patch`, `skyPortRenderPoly` PORT hook — geometry+texture reach GL, two unit defects open) and the full RDPHALF wire format is now decoded (S15.1 half-packing, 8-component perspective-interpolated vertex vectors); next session is mechanical per `docs/dev/D176a-SKY-NOTES.md`. `-level_36`/`-43` intro cams face down (not a sky test without `GE_INPUTSCRIPT`). **M-82: PR #18 rebased onto main + Defect-1 fix applied** — cloud tile is `s_skywaterimages[0]` = 64×64 IA8; the patch's `tc = S·32` scale is correct (matches GE's `width<<5` idiom, `glass2.c:678`), the bug was `(s16)` overflow on the ±20k-texel horizon S/T; fix = per-primitive phase-fold to the 64-texel period (`sky.c` `skyPortRenderPoly`, `#ifdef PORT`). Builds clean, no crash (bunker1/statue/surface1 verify PASS). **Unverified visually** — owed: one `-level_22` screenshot (see `D176a-SKY-NOTES.md` "verification ask"). Defect 2 (horizon-band coverage / straddling tris) still open → adaptive tessellation. **(b)** tree/rock static: **M-36 triage — NOT the D159 family.** `texSwapAltRowBytes` is a full `#ifdef PORT` no-op (`image.c:2199`), it cannot cause this. Real cause: `port/fast3d/gfx_pc.cpp` `import_texture_*` assume `line_size_bytes == full_image_line_size_bytes` (`SUPPORT_CHECK`; rgba16's is commented out *"trips ... with a garbage size"* `:658`) → non-PoT / sub-rect tiles get a flat linear read → diagonal row shear = grey static. **Family A** in `docs/dev/M-36-TRIAGE.md`. Fix: honour `line_size_bytes` as the real source pitch. Same defect as D182(2). |
 | **D174** | "No blood effect" — user reports no visible blood when shooting guards / into surfaces. | **User QA report; likely D120, unverified.** Decals: the D120 `PointUsage[]` converter fix (M-30) was never interactively verified and only takes effect after a full sidecar regen (`d43 && d69 && d88 --regen`) — check whether the playtest build had regenerated sidecars before concluding the fix failed. Spray: D172 observed the particle spray *drawing* (wrong color, magenta/cyan) on Silo — if the user sees no spray either, that's new info (different weapon/range, or the D172 decode is worse than "wrong color"). First step: BUNKER1 firefight with regenerated sidecars; if decals still absent, instrument the `chr.c:3328` decal walk. |
 | **D173** | Third-person Bond model (the player-representing figure shown at level start) spawns too high — floats well above the ground "a lot of the time" while the actual player spawn is correct. Same symptom on the Cuba end credits: JB stands ~6 ft in the air above Natalya. | **Confirmed still present across the full 21-level playthrough (M-49).** **Observed, not investigated** (user QA report). D75 animated-model family but a *position* defect, not absence — M-33 confirmed the gun-barrel Bond renders fine upright. Suspects: (a) intro/credits puppet chr spawn position vs the model's base transform; (b) anim root-motion accumulation (`modelSetAnimFrame2WithChrStuff`, D156 area) offsetting the rendered joints above the body origin; (c) a `coord3d`/packed-float decode in the intro camera/model setup. "Player spawning is OK" localises it to the render-side model, not `g_CurrentPlayer` state. |
 | **D182** | SELECT FILE screen degrades after navigating away and back (main menu → file select, or backing out of file select and re-entering). On the fresh screen the 007 gun-barrel spiral / Bond silhouette renders behind the file boxes; after a round-trip **the Bond image stops drawing entirely** and the whole background gains the **comb / interlacing** artifact (horizontal line scramble). File boxes, text and the Copy/Erase icons still draw. | **Observed, screenshot committed** (M-35, user QA; `docs/img/bugs/d182-file-select-backout-20260902.png`). Two symptoms, likely linked: **(1)** background 3D image stops rendering after re-entry → a front-end model/DL whose `render_pos` / segment binding is only valid on first construction (D149 / D75 `constructor_menuXX` family — the dossier/wallet models have the same "renders once" behavior). **(2)** interlacing = **M-36 triage: Family A**, the `import_texture_*` `line` vs `full_image_line` shear (see D176(b) / `docs/dev/M-36-TRIAGE.md`) — **not** the D159 `texSwapAltRowBytes` path (that is a full PORT no-op). Open question: why only *after* a round-trip — first import may land `line == width`, re-import may not, or the tile descriptor is stale on re-entry. Repro: `GE_STARTMENU` to file-select, back out with ESC/B, re-enter; `GE_DTEX` on the spiral texture across both visits. Shares defect (2) with D176(b). |