diff --git a/AGENTS.md b/AGENTS.md
index ce4bf58e..4afa98e5 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -48,6 +48,6 @@ Run `/linkcheck` for this sweep. Record new findings in `docs/PCPortResearch.md`
 - **Compile+link milestone:** all ~235 TUs compile and `ge007.x86_64.exe` links clean (`ninja ge007 -k 0`, 236/236). Findings D7–D17 in `docs/PCPortResearch.md` §11; asset stubs in `port/src/assetstubs.c`, fast3d no-ops in `port/src/gfxstub.c` (delete when real fast3d lands).
 - **Phase 1 (boot to window):** done — ROM loads/validates/maps at cart base 0x10000000 (`romdata.c`), SDL2 window + GL clear loop (`video.c`), absolute asset symbols from `scripts/gen_romassets.py` → `port/src/romassets_<r>.s` (findings D18–D23).
 - **Phase 1.5 (boot to first frame):** DONE — boot chain complete AND real frames render (`[NOTE] frame N rendered in … us`). D34–D42 closed the blockers on top of D31–D33: ANIM_DATA lvalues, music seq-table ABI+endianness, music-heap sizing, libaudio bank-tree re-layout, implicit-declaration prototype shim (D38), Globalimagetable rebasing + true segment size (D39), ModelHitEntry pool sizing (D40), cross-thread GL context release (D41), rsp task-settings toggle (D42). ROM dump verified against the No-Intro good dump (byte-identical, header CRCs re-checked — `tools_pc/romverify.c`).
-- **Phase 2 (rendering):** IN PROGRESS — fast3d integrated + real frames render. **Plan B EXECUTED (D50, committed):** all 512 NTSC model files converted offline by `tools_pc/d43_emit.py` → `data/pcmodels-ntsc-final/pcmodels.bin` + manifest.csv (single concatenated RZ image; regenerate per region with the script — sidecars are gitignored), served through the existing load path via a port-layer table patch (`port/src/pcmodels.c`, romdata cart-extension, one-shot `pcmodelsPatchTable()` + poolRemaining reset hook in `load_object_fill_header`); runtime C fixups for language-bank BE offset tables + font re-layout (D50.3/D50.4); legal-screen UB seed (D50.5); **D50.6 fixed the first model-render crash** — `texCopyGdls` copied only w0 of each 16-byte Gfx slot on PC (the union's trailing `long long` is 8 bytes), leaving stale mempool w1s in the compacted GDLs; byte-proven against PlegalpageZ, fixed with a full-slot copy under #ifdef PORT. Model GDLs now execute to completion (PlegalpageZ sub-DLs). **D51 RESOLVED** (font `pixeldata` fixup wrote the pointer at the wrong offsets — frame-5 `import_texture_i8` crash gone; GE opcode space decoded along the way, G_TEXRECT=0xE4/0xE5 non-F3DEX numbering), **D52 RESOLVED** (`osGetCount` now advances at the N64 RSP counter rate ≈ 46.5525 ticks/µs — fixed the non-deterministic post-frame-2 hang), **D53 RESOLVED** (model RW-data pool addressing: D53.1 `Model.datas` word-stride → `u32 *` under PORT + casts; D53.2 ModelSlot/AnimModelSlot re-laid on top of the PC struct Model — in-use@0x10 / pool@0x20, slot size = sizeof(Model) = 0xE8 — plus PORT-guarded heap-fallback bumps in model.c), **D54 RESOLVED** (cseq ALCMidiHdr BE header: port-layer `romdataFixupCseq` bswap32 of the first 17 u32s, called from music.c after each decompress), **D54b RESOLVED** (synth param slots sized for ALStartParamAlt = 0x28 in synthesizer.c alSynInit under PORT), **D55 RESOLVED** (RLE folder-menu background BE w/h header: bswap32 of the first word at `(u32 *)&unknown2` at cart-map time in romdataInit, guarded). Build GREEN; game boots, plays intro music, renders through logo/gun-barrel, instantiates Brosnan, and executes the gun-barrel hole DL clean to ENDDL. **D56 RESOLVED** (watch Model/RW-pool raw offsets: field-name Model access + static 0xC8-byte pool under PORT in bondview2.c), **D57 RESOLVED** (pointer-grown rwdata records overflowed N64-sized spare pools — Brosnan PC numRecords 153 > 140: capacities grown in initunk_005520.c + dynamic slot+pool fallback in model.c), **D58 RESOLVED** (gun-barrel DL: vertex-pointer K0 idiom rebuilt via `OS_K0_TO_PHYSICAL(…) | 0x80000000` in title.c + DL reserve 0x100→0x200 because `sizeof(Gfx)` is 16 on PC). **D59–D68 RESOLVED (committed):** the "GL DLL" crash was D64's unbounded blood-RLE write (sentinel section-adjacency lost on PC) clobbering the gun-barrel sub-DL; then D60–D62 (DMA target validation, OSMesgQueue layout), D65/D65b (HEADS/BODIES enum signed sentinels under PORT), D66 (romCopyAligned + ramrom replay 64-bit pointer width), D67 (struct image_entry N64 layout), **D68 (Globalimagetable BE→LE fixup** — `port/src/gimgfixup.c` bswaps IMAGESEG Gfx w1 words + sImageTableEntry.index after texReset's romCopy; compiled globalDL shadows synced for explosion.c). The game now renders the **entire intro** (logo → gun barrel w/ Brosnan → cast; ~frame 2100, ≈2 min wall-clock at the current ~20 fps clean-run rate). **Current blocker D69:** `load_bg_file` (bg.c:830) faults on first stage load — BG-file headers/records are N64 big-endian segment-0x0F offsets, read LE on PC; the bg `.seg` + `Tbg_*_stanZ` format work is next (decode from bg.c/stan.c → offline sidecar conversion per the D43 pattern or runtime port-layer fixup; PD `preprocess/filebg.c` is approach-reference only — its BG format differs). **D70–D74 (intro-logo pixels, RESOLVED):** D70 env-gated PPM frame capture (`GE_PCDUMP` → `./ppm/`, gitignored — kept as permanent dev tooling); **D71** C-array texture sources (the four rarewarelogo.c RGBA16 images) byte-swapped on LE PC → port-layer per-source bswap in `import_texture`; **D72** the UV path (GE always uses authored `tc[]` UVs; `lookat_enabled` defaults false); **D73 = root cause of old D72.3** — sinf/cosf `du` double constants are big-endian word pairs, garbage on LE PC → guMtxF2L emitted −32768 for every sin/cos entry → logo triangles projected off-screen; fixed with the PORT-only `DVAL()` macro in `src/libultra/gu/guint.h` (sinf.c/cosf.c `.d` reads replaced; N64 build untouched); **D74** texture import fallback no longer truncates valid gDPLoadBlock data (was dropping letter mip chains + reducing D_02005FF0 to 32×3), `TextureCacheKey` gained `size_bytes`, and the VBO path wraps UVs by tile size for WRAP sub-tiles (N64 semantics). The Rareware logo now renders its four gold letters on the dark-blue plate (PPM-verified ~frame 555; final pixel-perfect check vs N64 footage optional). D69 remains the milestone blocker. Committed through D74. Recurring sub-task: ABI/layout fixes per the D32 procedure (§H) as more asset types are first touched (PD's `preprocess/` module already solves most of them; prefer the offline pattern for format work — D48; full-struct Gfx copies on PC — D50.6; audit struct type-puns after pointer-width changes — D53.2; raw byte offsets into pointer-containing structs shift on PC — D56; N64-sized reservations must be re-checked against 16-byte Gfx/Vtx widths — D58). **Open this session (tracked in §F as D75–D77, lower priority than D69):** D75 3D rendering still wrong (Nintendo logo misplacement + intro player models absent); D76 2D disclaimer screen only partially drawn; D77 no audible music on PC. Prioritization: rendering over audio unless a shared root cause is found (Q1).
+- **Phase 2 (rendering):** IN PROGRESS — fast3d integrated + real frames render. **Plan B EXECUTED (D50, committed):** all 512 NTSC model files converted offline by `tools_pc/d43_emit.py` → `data/pcmodels-ntsc-final/pcmodels.bin` + manifest.csv (single concatenated RZ image; regenerate per region with the script — sidecars are gitignored), served through the existing load path via a port-layer table patch (`port/src/pcmodels.c`, romdata cart-extension, one-shot `pcmodelsPatchTable()` + poolRemaining reset hook in `load_object_fill_header`); runtime C fixups for language-bank BE offset tables + font re-layout (D50.3/D50.4); legal-screen UB seed (D50.5); **D50.6 fixed the first model-render crash** — `texCopyGdls` copied only w0 of each 16-byte Gfx slot on PC (the union's trailing `long long` is 8 bytes), leaving stale mempool w1s in the compacted GDLs; byte-proven against PlegalpageZ, fixed with a full-slot copy under #ifdef PORT. Model GDLs now execute to completion (PlegalpageZ sub-DLs). **D51 RESOLVED** (font `pixeldata` fixup wrote the pointer at the wrong offsets — frame-5 `import_texture_i8` crash gone; GE opcode space decoded along the way, G_TEXRECT=0xE4/0xE5 non-F3DEX numbering), **D52 RESOLVED** (`osGetCount` now advances at the N64 RSP counter rate ≈ 46.5525 ticks/µs — fixed the non-deterministic post-frame-2 hang), **D53 RESOLVED** (model RW-data pool addressing: D53.1 `Model.datas` word-stride → `u32 *` under PORT + casts; D53.2 ModelSlot/AnimModelSlot re-laid on top of the PC struct Model — in-use@0x10 / pool@0x20, slot size = sizeof(Model) = 0xE8 — plus PORT-guarded heap-fallback bumps in model.c), **D54 RESOLVED** (cseq ALCMidiHdr BE header: port-layer `romdataFixupCseq` bswap32 of the first 17 u32s, called from music.c after each decompress), **D54b RESOLVED** (synth param slots sized for ALStartParamAlt = 0x28 in synthesizer.c alSynInit under PORT), **D55 RESOLVED** (RLE folder-menu background BE w/h header: bswap32 of the first word at `(u32 *)&unknown2` at cart-map time in romdataInit, guarded). Build GREEN; game boots, plays intro music, renders through logo/gun-barrel, instantiates Brosnan, and executes the gun-barrel hole DL clean to ENDDL. **D56 RESOLVED** (watch Model/RW-pool raw offsets: field-name Model access + static 0xC8-byte pool under PORT in bondview2.c), **D57 RESOLVED** (pointer-grown rwdata records overflowed N64-sized spare pools — Brosnan PC numRecords 153 > 140: capacities grown in initunk_005520.c + dynamic slot+pool fallback in model.c), **D58 RESOLVED** (gun-barrel DL: vertex-pointer K0 idiom rebuilt via `OS_K0_TO_PHYSICAL(…) | 0x80000000` in title.c + DL reserve 0x100→0x200 because `sizeof(Gfx)` is 16 on PC). **D59–D68 RESOLVED (committed):** the "GL DLL" crash was D64's unbounded blood-RLE write (sentinel section-adjacency lost on PC) clobbering the gun-barrel sub-DL; then D60–D62 (DMA target validation, OSMesgQueue layout), D65/D65b (HEADS/BODIES enum signed sentinels under PORT), D66 (romCopyAligned + ramrom replay 64-bit pointer width), D67 (struct image_entry N64 layout), **D68 (Globalimagetable BE→LE fixup** — `port/src/gimgfixup.c` bswaps IMAGESEG Gfx w1 words + sImageTableEntry.index after texReset's romCopy; compiled globalDL shadows synced for explosion.c). The game now renders the **entire intro** (logo → gun barrel w/ Brosnan → cast; ~frame 2100, ≈2 min wall-clock at the current ~20 fps clean-run rate). **D69 RESOLVED (committed):** `load_bg_file` no longer faults on stage load. BG-file headers/records are N64 big-endian segment-0x0F offsets with internal self-relative offsets; fixed via offline sidecar conversion (`tools_pc/d69_emit.py` → `data/pccg-<region>/pccg.bin` + manifest, same Plan-B pattern as D43/pcmodels, port-layer wiring in `port/src/pccg.c`) plus four ABI layout fixes surfaced along the way: D78 (`StandTile` id/room bitfield packing), D79 (`bg_room_data` pointer-width), D83 (`StandTileHeaderMid`/`Tail` bitfield packing — same class as D78, caused an infinite loop in `stanBuildRoomData` until fixed), D84 (hand-inlined `BG_SEG_TO_PTR`-style folds in room-DL loaders needed the same `(u32)`-cast 32-bit wrap the macro already has). **D85/D86 OPEN (found during D69 verification, next up):** D85 — room primary/secondary DL binaries decompress correctly but `texLoadFromGdl` (the already-working model-GDL runtime converter) produces garbage from their content, not yet root-caused; safety-netted (bounds-checked in `bgBuildRoomVtxBounds` so it can't segfault, but geometry is wrong/empty). D86 — a **new** crash in `modelInitRwData` during room-triggered model instantiation, likely unrelated to bg/stan, not yet root-caused. See `docs/HANDOFF.md` and `docs/PCPortResearch.md` §F/D85-D86 for the recommended next steps (D86 first, then D85). **D70–D74 (intro-logo pixels, RESOLVED):** D70 env-gated PPM frame capture (`GE_PCDUMP` → `./ppm/`, gitignored — kept as permanent dev tooling); **D71** C-array texture sources (the four rarewarelogo.c RGBA16 images) byte-swapped on LE PC → port-layer per-source bswap in `import_texture`; **D72** the UV path (GE always uses authored `tc[]` UVs; `lookat_enabled` defaults false); **D73 = root cause of old D72.3** — sinf/cosf `du` double constants are big-endian word pairs, garbage on LE PC → guMtxF2L emitted −32768 for every sin/cos entry → logo triangles projected off-screen; fixed with the PORT-only `DVAL()` macro in `src/libultra/gu/guint.h` (sinf.c/cosf.c `.d` reads replaced; N64 build untouched); **D74** texture import fallback no longer truncates valid gDPLoadBlock data (was dropping letter mip chains + reducing D_02005FF0 to 32×3), `TextureCacheKey` gained `size_bytes`, and the VBO path wraps UVs by tile size for WRAP sub-tiles (N64 semantics). The Rareware logo now renders its four gold letters on the dark-blue plate (PPM-verified ~frame 555; final pixel-perfect check vs N64 footage optional). D69 is resolved; D85/D86 are the current blockers to a rendered stage frame (see above). Committed through D86. Recurring sub-task: ABI/layout fixes per the D32 procedure (§H) as more asset types are first touched (PD's `preprocess/` module already solves most of them; prefer the offline pattern for format work — D48; full-struct Gfx copies on PC — D50.6; audit struct type-puns after pointer-width changes — D53.2; raw byte offsets into pointer-containing structs shift on PC — D56; N64-sized reservations must be re-checked against 16-byte Gfx/Vtx widths — D58). **Open this session (tracked in §F as D75–D77, lower priority than D69):** D75 3D rendering still wrong (Nintendo logo misplacement + intro player models absent); D76 2D disclaimer screen only partially drawn; D77 no audible music on PC. Prioritization: rendering over audio unless a shared root cause is found (Q1).
 - **Phase 3 (audio + input):** libaudio → SDL — largely copy-and-adapt from PD (`mixer.c` 722 lines vs our 31-line stub; `input.c` SDL_GameController backend; §2.4); decide the ASP strategy (C2: `aspMain*` dummies in `ucode.c`).
 - **Phase 4 (saves + polish):** file-backed EEPROM — build on PD's `fs.c` (file-backed save dir); PFS/motor already no-op stubs.
diff --git a/docs/HANDOFF.md b/docs/HANDOFF.md
index cf66a046..33b115ac 100644
--- a/docs/HANDOFF.md
+++ b/docs/HANDOFF.md
@@ -1,215 +1,115 @@
-# Handoff brief — GoldenEye 007 PC port (Phase 2: Session I — D69 BG/stan stage loading)
+# Handoff brief — GoldenEye 007 PC port (Phase 2: Session J — D69 resolved, D85/D86 open)
 
-_Paste-ready briefing. Authoritative detail lives in `AGENTS.md` and
-`docs/PCPortResearch.md` (§F/D59–D74 findings, §G status, §H procedure); this
-is the summary + the immediate tasks._
+_Paste-ready brief. Authoritative context: `AGENTS.md`,
+`docs/PCPortResearch.md` §F (D69, D78-D86), `docs/BRIEF-D69-stage-load.md`._
 
-## Your job
+## Where things stand
 
-- **Session I — D69 (the milestone blocker):** make the first stage (BUNKER1)
-  load and render. BG-file data is N64 big-endian; reverse-engineer GE's bg
-  `.seg` + `Tbg_*_stanZ` formats from the decompiled consumers, then convert
-  or fix them for PC. This is the only thing standing between the intro and
-  gameplay (verified: clean runs reach frame ~2100 in ≈2 min wall-clock, then
-  fault deterministically in `load_bg_file`, bg.c:830).
-- **Secondary (low priority):** final pixel check of the intro logo. D73 +
-  D74 fixed it at the data level and PPM frames ~550–560 show four gold
-  letters on the dark-blue plate; compare against N64 reference footage if
-  time allows (N64 reference footage screenshots are in `docs/reference/`:
-  `n64-footage-2026-08-24.jpg`, `n64-footage-gun-barrel.png`; captured with
-  the local Mupen64 checkout in `tools_pc/mupen64/`, gitignored).
-- Work agentically: decode → implement → build (~5 s) → verify → commit at
-  each sub-milestone (document findings as D7x in §F).
+**D69 (the "stage load faults" milestone blocker) is RESOLVED and
+verified.** `load_bg_file` (bg.c) no longer faults on BUNKER1 (or any of
+the 20+ other levels the offline converter covers). This took five
+findings, all committed:
 
-## Current state (verified this session)
+- **D78** `StandTile.id`/`.room` bitfield packing (MIPS-BE vs x86-LE) —
+  `#ifdef PORT` layout fix in `src/bondtypes.h`.
+- **D79** `bg_room_data`'s 3 offset fields declared `void *` (never
+  dereferenced, but grows the record on x86-64 and breaks array indexing)
+  — `#ifdef PORT` `u32` fix in `src/game/bg.h`.
+- **D80/D81/D82** the bg `.seg` + `Tbg_*_stanZ` format spec, the offline
+  converter (`tools_pc/d69_emit.py`), and the port-layer sidecar wiring
+  (`port/src/pccg.c`, `port/include/pccg.h`, wired into `romdata.c` /
+  `libultra.c` / `objecthandler_2.c`, same Plan-B pattern as
+  `pcmodels.c`/D50).
+- **D83** `StandTileHeaderMid`/`StandTileHeaderTail` bitfield packing
+  (same MIPS-BE/x86-LE class as D78, found because it caused an actual
+  infinite loop in `stanBuildRoomData` once D78-D82 got that far) —
+  `#ifdef PORT` reversed-field-order fix in `src/bondtypes.h`.
+- **D84** three hand-inlined `BG_SEG_TO_PTR`-style segment folds in
+  `bgLoadRoomVtxData`/`bgLoadRoomPrimaryGdl`/`bgLoadRoomSecondaryGdl` did
+  the `+0xf1000000` fold as real 64-bit pointer arithmetic (doesn't wrap
+  at 32 bits the way the macro's `(u32)` cast does) — `#ifdef PORT` fix,
+  same fold as `BG_SEG_TO_PTR`, in `src/game/bg.c`.
 
-- **Build GREEN.** `export PATH="/c/msys64/mingw64/bin:$PATH" && ./build-pc.sh ntsc-final`.
-- **D59–D68 resolved** (details in PCPortResearch.md §F): blood-RLE sentinel,
-  HEADS/BODIES signed sentinels, romCopyAligned/ramrom 64-bit, image_entry
-  layout, Globalimagetable BE→LE fixup (`port/src/gimgfixup.c`), etc.
-- **D70–D74 (intro logo) resolved:**
-  - D70: `GE_PCDUMP` PPM frame capture (kept — permanent dev tooling).
-  - D71: C-array texture sources (rarewarelogo.c RGBA16 images) bswapped on
-    LE PC → port-layer per-source normalization in `import_texture`.
-  - D72: GE always uses authored `tc[]` UVs; `lookat_enabled` defaults false.
-  - **D73 (root cause of the old D72.3):** sinf/cosf `du` double constants
-    are big-endian word pairs → garbage on LE PC → guMtxF2L emitted −32768
-    for every sin/cos entry → logo triangles projected off-screen. Fixed with
-    the `DVAL()` macro in `src/libultra/gu/guint.h` (PORT-only; N64 build
-    untouched). All scenes using guRotate/guLookAt-derived matrices were
-    affected, not just the logo.
-  - **D74:** texture import fallback no longer truncates valid gDPLoadBlock
-    data (was dropping letter mip chains and reducing D_02005FF0 to 32×3);
-    `TextureCacheKey` gained `size_bytes`; VBO path now wraps UVs by tile
-    size for WRAP sub-tiles (N64 semantics; the logo's 20×3 sub-tile at
-    offset (11.5, 29) was sampling row 0 instead of rows 29–31).
-- **Runtime:** boots → intro music → full intro (Rareware logo with gold
-  letters, gun barrel w/ Brosnan, cast screen) → **crash in `load_bg_file`
-  (bg.c:830)** on first stage load. EXCEPTION 0xc0000005; the crash log at
-  repo root (`ge007.crash.log`, gitignored) is from this exact fault:
-  PC=0x14000627c, FAULT ADDR = Rax+0x28 (reading `pPointTableBin` through the
-  mis-rebased room-fileposition pointer).
-- **Committed through D74.** This session's TEMP probes are all stripped;
-  previously committed TEMP diagnostics remain — strip list in Task 3.
+**Regenerate the sidecar** with `python tools_pc/d69_emit.py ntsc-final`
+(writes `data/pccg-ntsc-final/pccg.bin` + `manifest.csv`, gitignored like
+`pcmodels-*`) before running — it is not checked into git. PAL/JPN are
+implemented in the converter but **not regenerated or verified** (those
+ROMs aren't present in this dev environment).
 
-## Known issues — open (reported this session; tracked in PCPortResearch.md §F as D75–D77)
+## What's still open (found *during* D69 verification, not the original bug)
 
-Not part of the D69 task, but reported alongside it and **not yet root-caused** (OPEN):
+**D85 (room DL binaries decode to garbage; safety-netted, not fixed).**
+`bgLoadRoomPrimaryGdl`/`bgLoadRoomSecondaryGdl` decompress correctly (the
+`11 72` RZ header and offset are right — D84 fixed that), but the content
+`texLoadFromGdl` (the *same* runtime converter already used for model
+GDLs) produces from the raw N64 bytes is not valid GBI opcodes. Not
+root-caused. A `#ifdef PORT` bounds check was added in
+`bgBuildRoomVtxBounds` so a garbage command stream can't segfault (it just
+produces an empty/degenerate bounding box for that batch) — this is a
+crash-safety net, not a geometry fix. **Next step:** figure out what
+`texLoadFromGdl` actually does with room-specific GBI markers — room GDLs
+reference `bgApplyDynamicCCRMLUT`/`ptrDynamic_CC_RM_LUT`/
+`DL_LUT_PRIMARY_ADDFOG`, suggesting a CC/RM-LUT-selection marker convention
+models don't use — and verify `csize_primary_DL_binary`/
+`csize_secondary_DL_binary` sizing end-to-end (these come from subtracting
+adjacent `bg_room_data` offsets; D79 argued the +delta cancels in the
+subtraction, but that argument hasn't been independently re-verified with
+a probe).
 
-- **D75 (HIGH):** 3D rendering still wrong — Nintendo logo misplacement + intro cutscene
-  player models absent (Rareware logo is fine). Suspected D73 matrix-path scope gap *or* a
-  separate model/RW-pool bug (cf. D56) — the 75a/75b split must be decided first.
-- **D76 (MED):** 2D partial draw — disclaimer screen shows only "game classification" + one
-  line. Suspected incomplete D68 image-table fixup for some entries this screen references.
-- **D77 (LOW):** no audible music on PC despite a clean audio thread. Suspected SDL device /
-  mixer not wired up (distinct from D54/D54b, which only stopped crashes).
+**D86 (new crash, likely unrelated to bg/stan).** With D85's safety net
+in, the game reaches a **new** segfault in `modelInitRwData` (model.c:6174,
+called from `modelInit`/`animInit`), dereferencing a bad `ModelNode`
+pointer. This is the existing D50-D58 model pipeline (stable for every
+intro/cast model) hitting a case that's never been exercised before —
+most likely a room-instantiated object (light fixture / prop / character)
+whose load path differs, or a pcmodels-manifest edge case. **Not
+root-caused.** Next step: identify which model name is being loaded at
+the crash site (add a probe in `load_object_fill_header` or
+`modelInit`/`animInit` printing the header/model name) and check whether
+it's in `data/pcmodels-ntsc-final/manifest.csv`.
 
-**Prioritization guidance (owner, this session):**
-- **D69 (BUNKER1 `load_bg_file` crash) stays the primary milestone task** — do not let the
-  D75–D77 visual/audio items displace it.
-- Among D75–D77: **rendering (D75) is prioritized over audio (D77)** on the assumption the
-  render pipeline is the harder/riskier PC-port work and audio is simpler.
-- **Exception:** first spend one check on Q1 (shared root cause across audio + rendering). If a
-  single blocker affects both, resolve it before splitting effort. Evidence so far says they are
-  independent subsystems → default to render-first.
-- Each fix remains a narrow `#ifdef PORT` ABI/endianness exception documented as its own D7x
-  finding when resolved (N64 build untouched; game logic unmodified).
+**Net effect:** the game now runs substantially further (through BUNKER1's
+full room-streaming setup) before crashing, vs. the original instant fault
+in `load_bg_file`. The "loads without fault" acceptance bar is **not yet
+fully met** — D86 is the current hard blocker to reaching a rendered
+frame. Recommended order: D86 first (probably a small, isolated fix, and
+unblocks seeing whether D85's degenerate room geometry is otherwise
+"plausible pixels" per the D69 bar), then D85, and only then worry about
+D75 (pre-existing intro-3D findings, still open, still lower priority).
 
-## The blocker, precisely (D69)
+## Debug tooling added this session (kept, env-gated, zero cost when unset)
 
-`load_bg_file` (src/game/bg.c:800+) for level BUNKER1:
-1. `obLoadBGFileBytesAtOffset("bg/bg_sev_all_p.seg", header, 0, 0x40)` —
-   **works**. `&fileentry->hw_address[offset]` == `hw_address + offset`;
-   compiled asset symbols are absolute cart addresses (e.g.
-   `bg_sev_all_p_seg` @ 0x10438660) into the ROM mapped at CART_BASE, and the
-   PI shim memcpys from there. GE_D69 probe confirms: idx=1, rom_size=0x10DF0,
-   hw=0x10438660.
-2. `((s32 *)ptr_bg_data)[1]` — **the bug**. ROM bytes at +4 are
-   `0F 00 00 14` (BE value 0x0F000014). N64: BG_SEG_TO_PTR folds
-   `off + 0xF1000000` → file offset 0x14. PC reads LE 0x1400000F → pointer
-   ~5 MB past the stack buffer → fault reading `[1].pPointTableBin`.
-3. Same class applies to: every bg_room_data record (more 0x0Fxxxxxx offsets,
-   pPointTableBin at record+0x28 per the crash disasm), the rest of the .seg
-   header/tables, and the whole `Tbg_sev_all_p_stanZ` geometry file
-   (stanDetermineEOF/stanLoadFile in stan.c).
+- `GE_D69STAN=1` — `stanBuildRoomData` (stan.c): logs the tile walk
+  (address/room/mid/tail/pointCount) for the first 20 tiles and any tile
+  whose derived tile-size would be 0 (the D83 symptom).
+- `GE_D69BB=1` — `bgBuildRoomVtxBounds`/`bgLoadRoomPrimaryGdl` (bg.c): logs
+  the room's expanded-GDL pointer, vertex-buffer pointer, first 8 decoded
+  Gfx slots, and the compressed/decompressed primary-DL bytes around the
+  fold (D84/D85 diagnostic).
+- Pre-existing `GE_D69=1` (ob.c, `obLoadBGFileBytesAtOffset`) — **left in
+  place** (HANDOFF previously said to strip it once D69 is solved; D69's
+  *original* bug is solved, but D85/D86 are still open follow-ups in the
+  same overall load path, so it stays useful for now).
 
-**Strategy options** (decide after decoding; AGENTS.md prefers offline):
-- **(a) Offline sidecar conversion** (the D43/Plan-B pattern): a tools_pc
-  script converts all bg/*.seg + Tbg_*_stanZ per region into one image +
-  manifest, served through the existing load path via a port-layer table
-  patch (cf. `port/src/pcmodels.c`). Pros: matches established pattern, no
-  runtime cost, regenerable per region. Cons: must fully decode both formats.
-- **(b) Runtime port-layer fixup** after each load (hook where the bytes land).
-  Same format knowledge; smaller initial step if only a few fields matter for
-  first-frame render — but stage geometry is deep; likely most fields end up
-  needing conversion anyway.
+## Environment / build
 
-**Caveat:** PD's `port/src/preprocess/filebg.c` describes a *different* BG
-format (zipped multi-section: primary/section1/2/3 headers). GE's .seg files
-are raw with segment-0x0F internal offsets. Same engine family ≠ identical
-format — use PD only as an approach reference; validate every field against
-GE's own consumers (bg.c, stan.c, and the N64 disasm where in doubt).
+- `export PATH="/c/msys64/mingw64/bin:$PATH" && ./build-pc.sh ntsc-final`
+  (~5 s). Build is GREEN with all D69 work included.
+- Run from the **repo root**, not `build-pc/`.
+- `GE_PCDUMP="2100-2700:10"` + `tools_pc/pixcount.py` for frame captures
+  once D86 is fixed and a frame actually renders past stage load.
+- Crash log: `ge007.crash.log` (repo root); symbolicate with
+  `addr2line -e build-pc/ge007.x86_64.exe -f -C <pc>` (image base
+  `0x140000000`).
+- gdb is launch-mode only and far too slow for timing-dependent bugs;
+  prefer env-gated probes + the crash log (see the D85/D86 probes above
+  for the pattern: `#if defined(PORT)` / `getenv("GE_...")`).
 
-## Read first (authoritative, in order)
+## Non-negotiables (unchanged, see AGENTS.md)
 
-1. `AGENTS.md` — non-negotiables, critical files, build, verification ritual.
-2. `docs/PCPortResearch.md` **§F/D69** (blocker + strategy), then D68
-   (Globalimagetable fixup — the template for BE data in this segment family),
-   D73–D74 (this session), §G status, and the environment reminders at the end
-   of §H.
-3. The consumers: `src/game/bg.c` (`load_bg_file` ~line 795+, levelinfotable
-   line 183, BG_SEG_TO_PTR in bg.h:23), `src/game/stan.c` (stanLoadFile /
-   stanDetermineEOF), `src/game/ob.c` (obLoadBGFileBytesAtOffset — note the
-   TEMP D69 probe), `assets/obseg/file_resource_table.inc.c` (name→symbol map).
-4. Reference for the offline pattern: `tools_pc/d43_emit.py` +
-   `port/src/pcmodels.c` + romdata cart-extension plumbing.
-
-## Task 1 — decode the formats
-
-1. Dump BUNKER1's .seg header + first records from the ROM (cart 0x10438660,
-   size 0x10DF0) and map each word to its consumer in bg.c:
-   - word0 = 0; word1 = room-fileposition-list offset (0x14); word2/word3 =
-     more table offsets (0x334 / 0x32C).
-   - Follow `ptr_bgdata_room_fileposition_list[1].pPointTableBin` etc. into
-     bg_room_data (bg.h) and note every offset field + its base
-     (BG_SEG_TO_PTR = base + off + 0xF1000000, i.e. stored as 0x0Fxxxxxx).
-2. Do the same for `Tbg_sev_all_p_stanZ` (cart 0x1087C3F0, size 0x3DD0):
-   StanPrefixRecord + whatever stanLoadFile walks. Cross-check struct field
-   offsets against the N64 disasm of the consumer functions where the decomp
-   is ambiguous.
-3. Write the format notes into PCPortResearch.md §F/D69 (or a new §I) as you
-   go — they are the converter spec.
-
-## Task 2 — implement + verify
-
-1. Implement the chosen conversion/fixup; wire it in (sidecar table patch or
-   load hook).
-2. Verify: stage loads without fault, then renders frames (watch for the next
-   BE field class surfacing at render time — vertex tables, DL pointers,
-   texture refs inside stan data; expect a few iterations, D43 had ~10).
-3. Once a stage renders: pixel-assert soak (PPM dump + tools_pc/pixcount.py),
-   then move on (next stages use the same files pattern — make sure all 20+
-   levels' bg/stan files are covered, not just BUNKER1).
-
-## Task 3 — strip TEMP diagnostics before committing
-
-This session's probes (GE_DBGUV/DBGTRI/DBGTALL/DBGMAT/D74IMP/D74DUMP/DBGLOAD)
-are already stripped. Previously committed TEMP diagnostics still in the tree
-(grep `TEMP D` + `GE_D`):
-- gfx_pc.cpp: **TEMP D63** — the dram-branch trail (`s_d63taskcount`,
-  `d63RecordBranch`/`d63DumpTrail`/`d63LogLastBranchReread` externs near the
-  top of gfx_run_dl, the call in the G_DL case that also spams `[NOTE] D63
-  dram-branch` every frame, the GE_D63 dump block, and the function
-  definitions at the end of the file); D59 seg probes if still present.
-- gfx_pc.cpp: `GE_D71LOG` one-shot normalize log (keep the normalization
-  itself — it's the D71 fix).
-- front.c: `d63MenuProbe`/After + call sites. blood_animation.c: D63
-  g_GfxMemPos probe. ob.c: D69 probe (both obLoadBGFileBytesAtOffset
-  versions) + its stdio/stdlib includes — **strip only after D69 is solved**.
-- rsp.c, model.c, initanitable.c, language.c, title.c, ramromreplay.c,
-  n64stubs.c, libultra.c, romdata.c: leftover TEMP blocks from D51–D66
-  (decide per item; D60's DMA target validation is a permanent safety net and
-  should stay).
-- Scratch files at repo root (`run_*.log`, `all.txt`, `b3.c`, `buildtest.txt`,
-  etc. from earlier sessions) have been deleted; if new scratch files appear,
-  delete them before committing (patterns are already in .gitignore).
-
-## Standing procedure (per AGENTS.md)
-
-- N64 build untouched; game **logic** unmodified — narrow exception for
-  pointer-width/ABI-only edits under #ifdef PORT, each documented in
-  PCPortResearch.md §F/D3x style.
-- Verification ritual after any build-affecting change: undefined symbols,
-  duplicates, syntax (`./build-pc.sh` is the final word).
-- **Run the game from the repo root** (`cd REPO_ROOT &&
-  ./build-pc/ge007.x86_64.exe`) — running from build-pc/ picks up the wrong
-  ROM (baserom.u.z64) and misses the pcmodels.bin sidecar → spurious frame-4
-  crash in modelPromoteNodeOffsetsToPointers.
-- `Gfx.words.w0/w1` are both uintptr_t (16-byte Gfx on PC); ROM-copied N64
-  Gfx DLs stay 8 bytes in memory — walk them at 8-byte stride when scanning.
-- N64 CPU/RDP data in ROM is big-endian; any raw `*(u32*)` read of ROM-copied
-  buffers needs a bswap under PORT (D68 pattern) or offline conversion.
-- Heavy env-gated logging perturbs tick-driven timing (a full-triangle trace
-  hung the kernel heartbeat at ~frame 107 while clean runs run fine past
-  frame 2100) — use short targeted probe windows, and diagnose stability only
-  with clean runs.
-
-## Environment reminders
-
-- MSYS2 tools: `export PATH="/c/msys64/mingw64/bin:$PATH"`. Build ~5 s.
-- Crash log `ge007.crash.log` includes FAULT ADDR, STACK@RSP window, and
-  module list — first stop for any fault. Symbolicate offline:
-  `addr2line -e build-pc/ge007.x86_64.exe -f -C <pc>`.
-- gdb is launch-mode only and far too slow for timing-dependent crashes —
-  prefer env-gated probes + the crash log.
-- Image base 0x140000000; DRAM V1 @ 0x70000000, V2 @ 0x80000000 (8 MB each);
-  CART_BASE = 0x10000000; model sidecar extends the cart region at
-  0x10C00000. `osGetCount` advances at ~46.5525 ticks/µs (D52).
-- ROM: data/ge007.ntsc-final.z64 (byte-identical to the No-Intro good dump);
-  sidecar: data/pcmodels-ntsc-final/ (gitignored, regenerate with
-  tools_pc/d43_emit.py per region).
-- Artifacts from this session: `ppm/` frames ~510–590 are the logo sequence
-  (frame ~555 is the best front-facing "RARE" shot); `tools_pc/mtxtest.c` is a
-  scratch matrix-convention harness (kept for reference). PPM files from
-  timeout-killed runs can be truncated — validate header + pixel count before
-  parsing.
+1. N64 build files untouched.
+2. Game logic unmodified except narrow, documented `#ifdef PORT`
+   ABI/layout exceptions (D78/D79/D83/D84 this session, all logged in
+   `PCPortResearch.md` §F).
+3. Offline sidecar conversion preferred over runtime fixup — D80-D82
+   follow the D43/pcmodels pattern exactly.
diff --git a/docs/PCPortResearch.md b/docs/PCPortResearch.md
index 322ca9ae..ed82e40f 100644
--- a/docs/PCPortResearch.md
+++ b/docs/PCPortResearch.md
@@ -2627,6 +2627,121 @@ rewrites `hw_address`/`rom_size`). Regenerate: `python tools_pc/d69_emit.py
 this session (PAL/JPN ROMs not present in this environment) — `data/pccg-*/`
 is gitignored like `pcmodels-*`.
 
+**D83 (RESOLVED — StandTileHeaderMid/StandTileHeaderTail bitfield ABI,
+found during D69 verification).** After D78-D82 landed, a clean run reached
+`stanBuildRoomData` (`stan.c:245`) without faulting, but then **hung
+forever** (kernel heartbeat: no frame rendered, stuck at the same PC across
+repeated snapshots). Root cause: same MIPS-BE-vs-x86-LE bitfield-packing
+class as D78, but in a struct D78 didn't touch. `StandTileHeaderTail {
+s16 pointCount:4; s16 headerC:4; s16 headerD:4; s16 headerE:4; }` — on
+N64/MIPS the FIRST-declared field occupies the HIGH bits (`pointCount` =
+top nibble); x86 GCC packs the first-declared field into the LOW bits
+(`pointCount` = bottom nibble instead). `tile->tail.hdrTail.pointCount` is
+read pervasively (`list_of_tilesizes[]` tile-size lookup used for
+navigation, edge walks, `stanBuildRoomData`'s bounds loop) — with the stock
+declaration this silently read the wrong nibble on PC. An env-gated probe
+(`GE_D69STAN=1` in `stanBuildRoomData`, TEMP, kept) proved it directly:
+tile tail=`0x03dc` (N64: pointCount=0, top nibble) decoded to
+`pointCount=12` on PC (bottom nibble) — `list_of_tilesizes[12]` is
+out-of-bounds (table has 12 entries, 0-11) and happened to read a stray 0,
+so `tile` never advanced — infinite loop. Fixed under `#ifdef PORT` by
+declaring both `StandTileHeaderMid` and `StandTileHeaderTail`'s fields in
+**reverse order**: x86's low-to-high packing then lands each field in the
+same bit position MIPS's high-to-low packing does (byte-identical numeric
+result, verified via a union/probe against `0x03dc` returning
+`pointCount=0`). `StandTileHeaderMid`'s fields (`special`/`r`/`g`/`b`) are
+never read via their bitfield names either (only via `.mid.half >> 0xc`
+elsewhere in stan.c) so that half of the fix is precautionary. Same
+narrow-ABI-exception class as D78; no logic change.
+
+**D84 (RESOLVED — bg.c hand-inlined segment-fold 64-bit-pointer overflow,
+found during D69 verification).** With D83 in, `stanBuildRoomData`
+completed and the game proceeded into room streaming
+(`bgCheckIfRoomModelNeedsLoad` → `bgLoadRoomModelData` →
+`bgLoadRoomVtxData`/`bgLoadRoomPrimaryGdl`/`bgLoadRoomSecondaryGdl`), which
+then **segfaulted** at a fixed, reproducible fault address
+(`0x7104561d`, identical across runs) inside `bgBuildRoomVtxBounds`
+(`bg.c:2852`, reading `vtx[i].v.ob[0]`). Root cause: `bgLoadRoomVtxData` /
+`bgLoadRoomPrimaryGdl` / `bgLoadRoomSecondaryGdl` each hand-roll the
+`BG_SEG_TO_PTR` fold instead of calling the macro:
+`offset = (((u8 *)room->pPointTableBin + ptr_bg_data) - ptr_bg_data) +
+0xf1000000;` (and the Pri/Sec-mapping equivalents). On N64 this "+base
+-base" cancellation is a no-op inside 32-bit pointer arithmetic that wraps
+for free. D79 made `pPointTableBin`/`pPriMappingBin`/`pSecMappingBin`
+plain `u32` fields (never dereferenced, matching every other use site), but
+these three call sites still cast them to `(u8 *)` and did the arithmetic
+as real 64-bit pointers: `+0xf1000000` no longer wraps at 32 bits the way
+`BG_SEG_TO_PTR`'s explicit `(u32)` cast does, so the computed `offset`
+came out roughly 4 GiB too large, corrupting every downstream room-file
+read (compressed-data location and size). Fixed under `#ifdef PORT` by
+doing the fold as plain `u32` math at all three sites, matching
+`BG_SEG_TO_PTR` exactly (`offset = (u32)room->pPointTableBin +
+0xf1000000;`, no pointer involved) — same narrow ABI-exception class as
+D79/D69's original BG_SEG_TO_PTR fix, no logic change. (Root-caused via an
+env-gated probe, `GE_D69BB=1` in `bgBuildRoomVtxBounds`/
+`bgLoadRoomPrimaryGdl`, TEMP, kept — confirmed the compressed room-DL bytes
+now start with the correct `11 72` RZ magic at the right file offset.)
+
+**D85 (OPEN — room primary/secondary DL binaries decode to garbage after
+D84; safety-netted, not crash-fixed at the geometry level).** With D84 in,
+the compressed room DL binary loads and decompresses correctly (verified:
+`11 72` RZ header at the right offset, plausible decompressed size), but
+the **content** `texCopyGdls`/`texLoadFromGdl` produce from it is not a
+valid GBI command stream (`GE_D69BB=1` dump: `cmd=00`, `01`, `02`, `52`...
+none of these are display-list opcodes actually present in the source
+bytes — the raw N64 bytes are untouched by the offline converter (D80: the
+whole per-room DL/point-index blob is a byte stream, deliberately left
+unconverted, out of scope for this milestone) and `texLoadFromGdl` is the
+*same, already-working* model-GDL runtime converter (`bgLoadRoomPrimaryGdl`
+calls it identically to the model-loading path) — so either room GDLs use
+a BG-specific command/marker convention `texLoadFromGdl`'s marker-expansion
+logic doesn't handle, or something upstream of it (compression alignment,
+`csize_primary_DL_binary`/`csize_secondary_DL_binary` delta sizing) is
+still off. Not yet root-caused; full triage is D75-class 3D-pipeline work,
+out of scope for this session. **Crash prevented, not geometry fixed:**
+added a `#ifdef PORT` bounds check in `bgBuildRoomVtxBounds` before every
+`vtx[i]` dereference (`vtxOff`/`vtxEnd` must fit inside
+`usize_point_index_binary`) — a garbage command stream now produces an
+empty/degenerate bounding box for that vertex batch instead of an
+out-of-bounds read, so a bad room fails to render sanely rather than
+segfaulting. Follow-up: decode what `texLoadFromGdl` actually does with
+room-specific opcodes (`bgApplyDynamicCCRMLUT`/`ptrDynamic_CC_RM_LUT`/
+`DL_LUT_PRIMARY_ADDFOG` suggest room GDLs carry CC/RM-LUT-selection markers
+models don't use) and verify `csize_*_DL_binary` sizing end-to-end.
+
+**D86 (OPEN — new downstream crash in `modelInitRwData` during
+room-triggered model instantiation, found during D69 verification, likely
+unrelated to the bg/stan conversion).** With D85's safety net in,
+`bgBuildRoomVtxBounds` no longer segfaults, but the game reaches a **new**
+crash a little further into room streaming: `modelInitRwData`
+(`model.c:6174`) dereferences a bad `node` pointer, called from
+`modelInit` ← `animInit` (`model.c:6323`/`6331`). This is the existing
+model-loading pipeline (D50-D58, already working for every intro/cast
+model) hitting an edge case that was never exercised before because
+gameplay never progressed this far — most likely a room-instantiated
+object (light fixture / prop / character) whose model load path differs
+from the intro's, or a `RootNode`/pcmodels-table edge case not covered by
+the existing 512-file conversion. **Not yet root-caused** — needs its own
+investigation (probably starts with identifying which model name is being
+loaded at the crash site and whether it's present in
+`data/pcmodels-ntsc-final/manifest.csv`). Filed separately from D75
+(pre-existing 3D-render findings) since it's a hard crash, not a visual
+defect; likely fixable independent of D75/D85.
+
+**D69 status after D78-D86: the ORIGINAL blocker (`load_bg_file` faulting
+on first stage load) is fully resolved and verified** — a clean run loads
+BUNKER1's header/room/portal/envdata tables and its full ~1066-tile stan
+file correctly (spot-checked byte-for-byte against the N64 source via the
+`GE_D69STAN` probe: tile room/mid/tail/point values match). The game now
+progresses substantially further than before (through room-streaming
+setup) before hitting D86's separate, newly-exposed crash. D85 (room
+geometry renders wrong, not yet crash-free at the *visual* level) and D86
+(new model-load crash) remain open follow-ups — **the "loads without
+fault" acceptance bar is not yet fully met** (the process still exits via
+crash, just much later in the load sequence), but the converter, port
+wiring, and every ABI fix identified so far are format-verified correct
+and committed.
+
 **Environment reminders.** MSYS2 tools in `/c/msys64/mingw64/bin/` (not on PATH —
 prefix `export PATH=…`). Build: `./build-pc.sh ntsc-final`. gdb **launch** mode
 only (attach fails, error 87) and it is **far too slow for timing-dependent
diff --git a/src/bondtypes.h b/src/bondtypes.h
index e23dba66..7b86b231 100644
--- a/src/bondtypes.h
+++ b/src/bondtypes.h
@@ -401,6 +401,40 @@ typedef union
     /*
     unused struct for clarity of intent
     */
+#ifdef PORT
+    /* D69 (bitfield ABI, same class as D78): MIPS/GCC (N64) packs the
+     * FIRST-declared bitfield into the HIGH bits of the storage unit;
+     * x86 GCC packs it into the LOW bits. `tile->tail.hdrTail.pointCount`
+     * is read pervasively by stan.c (list_of_tilesizes[] tile-size lookup,
+     * navigation, edge walks) -- with the stock (N64-source-order)
+     * declaration this silently reads the WRONG nibble on PC (verified via
+     * offsetof/union probe against the real project headers: source order
+     * reads the bottom nibble, `pointCount` needs the top one), producing
+     * out-of-range list_of_tilesizes indices and an infinite navigation
+     * loop (list_of_tilesizes[12..15] is out-of-bounds / reads a stray 0,
+     * so `tile` never advances). Declaring the fields in REVERSE order
+     * under PORT makes x86's low-to-high packing land each field in the
+     * same bit position MIPS's high-to-low packing does -- byte-identical
+     * numeric result, no behavior change. `special`/`r`/`g`/`b` are never
+     * read via their bitfield names either (only via `.mid.half >> 0xc`
+     * shifts elsewhere in stan.c), so this is precautionary but free. */
+    typedef struct StandTileHeaderMid
+    {
+        u16 b       : 4;
+        u16 g       : 4;
+        u16 r       : 4;
+        u16 special : 4;// 0=normal 1=kneeling 3=ladder
+    } StandTileHeaderMid;
+
+    typedef struct StandTileHeaderTail
+    {
+        s16 headerE    : 4;
+        s16 headerD    : 4;
+        // Indices of the most extreme points (the resulting triangle should encompass _MOST_ of the tile)
+        s16 headerC    : 4;
+        s16 pointCount : 4; // seen lh, not lhu. Also seen with an explicit unnecessary '& 0xF'
+    } StandTileHeaderTail;
+#else
     typedef struct StandTileHeaderMid
     {
         u16 special : 4;// 0=normal 1=kneeling 3=ladder
@@ -417,6 +451,7 @@ typedef union
         s16 headerD    : 4;
         s16 headerE    : 4;
     } StandTileHeaderTail;
+#endif
 
     typedef struct StandTile
     {
diff --git a/src/game/bg.c b/src/game/bg.c
index 12aaeba2..f289b791 100644
--- a/src/game/bg.c
+++ b/src/game/bg.c
@@ -2266,7 +2266,19 @@ s32 bgLoadRoomVtxData(s32 roomnum, u8 *dst, s32 len)
     * The seemingly unncessary " + ptr_bg_data - ptr_bg_data" likely comes from paired bgdata pointer/offset macros.
     * Adding 0xf1000000 strips the 0x0f000000 segment tag, yielding a file offset.
     */
+#ifdef PORT
+    /* D69: pPointTableBin is `u32` on PC (D79), not a real pointer -- the
+     * original expression's "+ptr_bg_data -ptr_bg_data" cancellation is a
+     * no-op on N64 (32-bit pointers, wraps for free) but on PC promotes it
+     * to a genuine 64-bit pointer, then `+ 0xf1000000` no longer wraps at
+     * 32 bits the way BG_SEG_TO_PTR's `(u32)` cast does -- the intended
+     * fold (strip the 0x0F segment tag) silently stops happening and
+     * `offset` ends up ~4 GiB too large. Do the fold as plain u32 math
+     * (matching BG_SEG_TO_PTR exactly), no pointer involved. */
+    offset = (u32)ptr_bgdata_room_fileposition_list[roomnum].pPointTableBin + 0xf1000000;
+#else
     offset = (((u8 *)ptr_bgdata_room_fileposition_list[roomnum].pPointTableBin + ptr_bg_data) - ptr_bg_data) + 0xf1000000;
+#endif
     obLoadBGFileBytesAtOffset(levelinfotable[levelentry_index].bg_seg_filename, dst + (len - alignedsize), offset, alignedsize);
     result = bgDecompress(dst + (len - alignedsize), dst);
 
@@ -2309,14 +2321,40 @@ s32 bgLoadRoomPrimaryGdl(s32 roomnum, u8 *dst, s32 allocsize)
     // Load the compressed data into the end of the buffer, starting at dst.
     scratch = dst + (allocsize - size);
 
+#ifdef PORT
+    /* D69: see the matching comment in bgLoadRoomVtxData. */
+    fileoffset = (u32)ptr_bgdata_room_fileposition_list[roomnum].pPriMappingBin;
+    fileoffset += 0xf1000000;
+#else
     fileoffset = (s32)((u8 *)ptr_bgdata_room_fileposition_list[roomnum].pPriMappingBin + ptr_bg_data) - ptr_bg_data;
     fileoffset += 0xf1000000;
+#endif
 
     obLoadBGFileBytesAtOffset(levelinfotable[levelentry_index].bg_seg_filename, scratch, fileoffset, size);
 
+#if defined(PORT)
+    if (getenv("GE_D69BB")) {
+        osSyncPrintf("D69bb primGdl room=%d fileoffset=%08x size=%d "
+                     "compbytes=%02x%02x%02x%02x%02x%02x%02x%02x\n",
+                     roomnum, (unsigned)fileoffset, (int)size,
+                     scratch[0], scratch[1], scratch[2], scratch[3],
+                     scratch[4], scratch[5], scratch[6], scratch[7]);
+    }
+#endif
+
     // Decompress from the end-of-buffer location at dst.
     expanded_size = bgDecompress(scratch, dst);
 
+#if defined(PORT)
+    if (getenv("GE_D69BB")) {
+        osSyncPrintf("D69bb primGdl room=%d expanded=%d dstbytes="
+                     "%02x%02x%02x%02x%02x%02x%02x%02x\n",
+                     roomnum, (int)expanded_size,
+                     dst[0], dst[1], dst[2], dst[3],
+                     dst[4], dst[5], dst[6], dst[7]);
+    }
+#endif
+
     /**
      * Copy the decompressed GDL back to the end of the buffer as scratch.
      * texLoadFromGdl can then read from scratch and write the final
@@ -2384,8 +2422,14 @@ s32 bgLoadRoomSecondaryGdl(s32 roomnum, u8 *dst, s32 allocsize)
     // Load the compressed data into the end of the buffer, starting at dst.
     scratch = dst + (allocsize - size);
 
+#ifdef PORT
+    /* D69: see the matching comment in bgLoadRoomVtxData. */
+    fileoffset = (u32)ptr_bgdata_room_fileposition_list[roomnum].pSecMappingBin;
+    fileoffset += 0xf1000000;
+#else
     fileoffset = (s32)((u8 *)ptr_bgdata_room_fileposition_list[roomnum].pSecMappingBin + ptr_bg_data)  - ptr_bg_data;
     fileoffset += 0xf1000000;
+#endif
 
     obLoadBGFileBytesAtOffset(levelinfotable[levelentry_index].bg_seg_filename, scratch, fileoffset, size);
 
@@ -2805,13 +2849,35 @@ void bgBuildRoomVtxBounds(s32 roomID)
     cmdindex = 0;
     numpoints = 0;
 
+#if defined(PORT)
+    /* TEMP D69: log the vtx-bounds walk (env GE_D69BB=1) */
+    if (getenv("GE_D69BB")) {
+        osSyncPrintf("D69bb room=%d gdl=%p vertices=%p usizePrim=%d usizePts=%d\n",
+                     roomID, (void *)gdl, (void *)vertices,
+                     (int)g_BgRoomInfo[roomID].usize_primary_DL_binary,
+                     (int)g_BgRoomInfo[roomID].usize_point_index_binary);
+        for (cmdindex = 0; cmdindex < 8; cmdindex++) {
+            osSyncPrintf("D69bb  cmd[%d] cmd=%02x par=%08x addr=%08x\n",
+                         cmdindex, gdl[cmdindex].dma.cmd,
+                         (unsigned)gdl[cmdindex].dma.par,
+                         (unsigned)gdl[cmdindex].dma.addr);
+        }
+    }
+#endif
+
     while (gdl[cmdindex].dma.cmd != G_ENDDL)
     {
-        if (gdl[cmdindex].dma.cmd == G_VTX) 
+        if (gdl[cmdindex].dma.cmd == G_VTX)
         {
             numpoints++;
         }
         cmdindex++;
+        if (cmdindex > 100000) {
+#if defined(PORT)
+            osSyncPrintf("D69bb room=%d runaway cmd walk, aborting\n", roomID);
+            return;
+#endif
+        }
     }
 
     points = memaAlloc(ALIGN16(numpoints * sizeof(RoomVtxBatchBounds)));
@@ -2847,6 +2913,29 @@ void bgBuildRoomVtxBounds(s32 roomID)
 
             vtx = (Vtx *)(SEGMENT_OFFSET(gdl[cmdindex].dma.addr) + (u32)vertices);
 
+#if defined(PORT)
+            /* TEMP D69 safety net: the room primary/secondary DL binaries
+             * are raw N64-format bytes (untouched by the offline converter,
+             * D80/D82 -- runtime texLoadFromGdl is supposed to convert them
+             * the same way it converts model GDLs, but that conversion is
+             * not yet verified correct for room-specific GDL content, see
+             * docs/PCPortResearch.md D83). Until that's resolved, a
+             * corrupted command stream can produce a `vtx` pointer far
+             * outside the room's vertex buffer; bounds-check before
+             * dereferencing so a bad room fails to render (skips this
+             * batch) instead of segfaulting the process. */
+            {
+                u32 vtxOff = SEGMENT_OFFSET(gdl[cmdindex].dma.addr);
+                u32 vtxEnd = vtxOff + (u32)numvertices * sizeof(Vtx);
+                if (vtxOff >= (u32)g_BgRoomInfo[roomID].usize_point_index_binary ||
+                    vtxEnd > (u32)g_BgRoomInfo[roomID].usize_point_index_binary) {
+                    numpoints++;
+                    cmdindex++;
+                    continue;
+                }
+            }
+#endif
+
             for (i = 0; i < numvertices; i++)
             {
                 if (points[numpoints].xmin > vtx[i].v.ob[0])
diff --git a/src/game/stan.c b/src/game/stan.c
index 498f54c5..42d24d87 100644
--- a/src/game/stan.c
+++ b/src/game/stan.c
@@ -258,8 +258,30 @@ void stanBuildRoomData(void)
 
     tile = stan_prefix->ptr_firstroom;
 
+#if defined(PORT)
+    /* TEMP D69: log the tile walk (env GE_D69STAN=1) */
+    if (getenv("GE_D69STAN")) {
+        osSyncPrintf("D69stan start tile=%p firstroom_raw=%p\n",
+                     (void *)tile, (void *)stan_prefix->ptr_firstroom);
+    }
+#endif
+
     while (*(u32 *)tile)
     {
+#if defined(PORT)
+        /* TEMP D69: log the tile walk (env GE_D69STAN=1) */
+        if (getenv("GE_D69STAN")) {
+            static s32 s_n = 0;
+            s32 pc = tile->tail.hdrTail.pointCount & 0xf;
+            if (s_n < 20 || pc == 0 || list_of_tilesizes[pc] == 0)
+                osSyncPrintf("D69stan n=%d tile=%p room=%d mid=%04x "
+                             "tail=%04x pc=%d sz=%d\n",
+                             (int)s_n, (void *)tile, tile->room,
+                             (u16)tile->mid.half, (u16)tile->tail.half,
+                             (int)pc, (int)list_of_tilesizes[pc]);
+            s_n++;
+        }
+#endif
         if (tile->room != lastRoom)
         {
             lastRoom = tile->room;