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_walk.py

@@ -0,0 +1,97 @@
+# D43 helper: walk every model file's node tree (N64 layout) and report
+# opcode histogram + structural sanity. Usage: python d43_walk.py
+import csv, struct, zlib, sys
+from collections import Counter
+
+ROM = r"data/ge007.ntsc-final.z64"
+rom = open(ROM, "rb").read()
+rows = list(csv.reader(open(r"scripts/filelist.u.csv")))
+
+OP={1:"HEADER",2:"GROUP",3:"OP03",4:"DL",5:"OP05",6:"OP06",7:"OP07",8:"LOD",9:"BSP",10:"BOX",11:"OP11",12:"GUNFIRE",13:"SHADOW",14:"OP14",15:"INTERLINK",16:"OP16",17:"OP17",18:"SWITCH",21:"GROUPSIMPLE",22:"DLPRIMARY",23:"HEADPH",24:"DLCOLLISION"}
+
+# N64 record sizes (bytes) per opcode, from bondtypes.h
+RSZ={1:0x10,2:0x1C,3:0x1C,4:0x14,5:0x1AC,6:0x18,7:0x1B0,8:0x10,9:0x24,10:0x1C,
+     11:0x50,12:0x28,13:0x20,14:0x10,15:0x1C,16:0x18,17:0x20,18:0x08,21:0x14,
+     22:0x10,23:0x02,24:0x20}
+
+# (numSwitches, numtextures) per model from the exe headers would be ideal;
+# instead parse assets/obseg/**/ModelFileHeader.inc.c + body records.
+import re, glob
+nsnt = {}
+import os
+hdrfiles = set()
+for root, dirs, files in os.walk("assets"):
+    for fn in files:
+        if fn.lower().endswith("modelfileheader.inc.c"):
+            hdrfiles.add(os.path.join(root, fn))
+nsnt = {}
+for f in sorted(hdrfiles):
+    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
+        name = a[0]
+        try:
+            NS = int(a[4], 0); NT = int(a[8], 0)
+        except ValueError:
+            continue
+        nsnt[name] = (NS, NT)
+
+# body/chr records live in other .inc.c files with the same macro? check c_item_entries etc.
+print("headers parsed:", len(nsnt))
+
+opcount = Counter()
+files_ok = 0
+files_bad = []
+total_nodes = 0
+maxP = 0
+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]
+    if not (base[0] in "CGP" and base.endswith("Z") and "_stan" not in base): continue
+    try: addr,size=int(r[0]),int(r[1])
+    except ValueError: continue
+    try: out = zlib.decompress(rom[addr:addr+size][2:], -15)
+    except Exception: files_bad.append((base,"decomp")); continue
+    D = len(out)
+    key = None
+    for cand in (base, base[1:], base[:-1], base[1:-1]):
+        if cand in nsnt:
+            key = cand; break
+    NS,NT = nsnt.get(key, (0,0)) if key else (0,0)
+    if NT is None:
+        # try to find NT from a record table elsewhere; fallback scan
+        files_bad.append((base,"no-NT"))
+        continue
+    root_off = 4*NS + 12*NT
+    def be16(o): return struct.unpack_from(">H", out, o)[0]
+    def be32(o): return struct.unpack_from(">I", out, o)[0] & 0xFFFFFF
+    seen = set()
+    ok = True
+    n = 0
+    stack = [root_off] if root_off < D else []
+    while stack:
+        o = stack.pop()
+        if o in seen or o >= D: ok=False; break
+        seen.add(o)
+        op = be16(o) & 0xff
+        opcount[op] += 1
+        n += 1
+        data = be32(o+4); child = be32(o+20)
+        if not (0 < data < D): ok=False; break
+        # validate record fits
+        rsz = RSZ.get(op, 0)
+        if rsz and data + rsz > D: ok=False; files_bad.append((base,"rec-overflow op%d @%X+%X>%X"%(op,data,rsz,D))); break
+        if child: stack.append(child)
+    total_nodes += n
+    if ok: files_ok += 1
+    else: files_bad.append((base,"walk-fail root=%X NS=%d NT=%d D=%X"%(root_off,NS,NT,D)))
+
+print("files ok:", files_ok, " bad:", len(files_bad))
+for b in files_bad[:20]: print("   ", b)
+print("total nodes:", total_nodes)
+print("opcode histogram:")
+for op in sorted(opcount):
+    print("  op%-3d %-12s x%d" % (op, OP.get(op,"??"), opcount[op]))