PC port: phase 2 — D48 review: re-plan D43 as offline pre-conversion (Plan B)

- D48 finding in PCPortResearch.md §F: d43_convert.py does not emit bytes
  (layout+remap validation only); Plan B = Python emit pass -> data/pcmodels-<region>/
  RZ sidecars served via port-layer hw_address/rom_size table patch (no C
  converter); Plan A kept as fallback with corrected staging guard (D_N64+D_PC<=avail)
- Moved all 23 d43_*.py investigation scripts from gitignored build-pc/ to tracked
  tools_pc/ (spec is now versioned); d43_cover.py path ref updated; converter
  re-run from new location: ALL CLEAN
- HANDOFF.md rewritten as two-session prompt: Session A = independent review of
  Plan B (8 claims, each with falsification criterion -> finding D49), Session B =
  execute (emit pass + round-trip validator, romdata plumbing, one-line hook,
  pixel-assert soak); verified-facts converter spec preserved
- AGENTS.md phase status updated to D48 re-plan

tools_pc/d43_lutscan.py

@@ -0,0 +1,101 @@
+#!/usr/bin/env python3
+"""Scan all model files' texture tables -> image headers -> format/maxlod.
+Determines whether any LUT textures (formats 9-12) exist, which affects
+worst-case marker expansion sizing (D45)."""
+import csv, struct, zlib, os, re
+from collections import Counter
+
+ROM = r"data/ge007.ntsc-final.z64"
+rom = open(ROM, "rb").read()
+
+imgrows = list(csv.reader(open("imagelist.u.csv")))
+img_off = [int(r[0]) for r in imgrows]
+img_sz = [int(r[1]) for r in imgrows]
+
+rows = list(csv.reader(open(r"scripts/filelist.u.csv")))
+
+nsnt = {}
+for root, dirs, files in os.walk("assets"):
+    for fn in files:
+        if fn.lower().endswith("modelfileheader.inc.c"):
+            f = os.path.join(root, fn)
+            for line in open(f):
+                m = re.search(r"MODELFILEHEADER\((.*)\)\s*;?\s*$", line)
+                if not m:
+                    continue
+                a = [x.strip() for x in m.group(1).split(",")]
+                if len(a) < 9:
+                    continue
+                try:
+                    nsnt[a[0]] = (int(a[4], 0), int(a[8], 0))
+                except ValueError:
+                    pass
+
+def bitread(buf, pos, n):
+    val = 0
+    for i in range(n):
+        byte = buf[pos >> 3]
+        bit = 7 - ((pos & 7) % 8)
+        val = (val << 1) | ((byte >> bit) & 1)
+        pos += 1
+    return val, pos
+
+fmtall = Counter()
+fmtlut = Counter()
+maxlod_dist = Counter()
+nimg = 0
+bad = 0
+zc = 0
+matched_files = 0
+lut_examples = []
+
+for r in rows:
+    if len(r) < 3 or not r[2]:
+        continue
+    base = r[2].rsplit("/", 1)[-1]
+    if base.endswith(".bin"):
+        base = base[:-4]
+    key = None
+    for cand in (base, base[1:], base[:-1], base[1:-1]):
+        if cand in nsnt:
+            key = cand
+            break
+    if not key:
+        continue
+    matched_files += 1
+    NS, NT = nsnt[key]
+    addr, size = int(r[0]), int(r[1])
+    out = zlib.decompress(rom[addr:addr + size][2:], -15)
+    D = len(out)
+    texoff = 4 * NS + 12 * NT
+    for i in range(NT):
+        tid = struct.unpack_from(">I", out, texoff + i * 12)[0]
+        if tid >= len(img_off):
+            bad += 1
+            continue
+        nimg += 1
+        o = img_off[tid]
+        s = img_sz[tid]
+        hdr = rom[o]
+        iszlib = (hdr & 0x40) >> 6
+        lod = hdr & 0x3f
+        maxlod_dist[min(lod, 7)] += 1
+        if iszlib:
+            zc += 1
+            fmt = (rom[o + 1] >> 4) & 0xf
+        else:
+            b2 = rom[o + 1:o + s]
+            fmt, _ = bitread(b2, 0, 4)
+        fmtall[fmt] += 1
+        if fmt in (9, 10, 11, 12):
+            fmtlut[fmt] += 1
+            if len(lut_examples) < 10:
+                lut_examples.append((key, i, tid, fmt))
+
+print("nsnt entries:", len(nsnt))
+print("matched model files:", matched_files, "tex refs:", nimg, "bad:", bad, "zlib:", zc)
+print("formats used:", dict(sorted(fmtall.items())))
+print("LUT formats (9-12):", dict(fmtlut))
+print("maxlod dist:", dict(sorted(maxlod_dist.items())))
+for e in lut_examples:
+    print("  LUT example:", e)