D125: fix d88_emit.py:374 8-byte slice / 4-byte literal (Aztec C3 crash)

emit_pad()'s widened-stan zero-fill assigned a 4-byte literal to an
8-byte bytearray slice. Python slice-assign with a short RHS silently
deletes the surplus bytes, so `out` shrank 4 B per pad+boundpad; once
len(out) dropped below a later leaf write's target offset, the write
clamped to empty-at-end and inserted there, drifting/truncating the
boundpad plink-name blob (Aztec pad33 "p138d2" -> "8d2") -> stanPackId
reject -> NULL stan -> door model=NULL -> crash propobj.c:13601.

Fix: 8 NUL bytes (only width-mismatched out[ write in the file).
All 21 Usetup*Z sidecars regenerated. Aztec (-level_28) now PASSES
(was C3 CRASH); Bunker1/Silo unregressed; d125_check.py 21/21 MATCH.
Sweep 12 -> 13/21.

Bunker2 (-level_27) still crashes: separate DOOR-tail linkedDoor
layout bug in d88_propdefs.py (C3r) -- linkedDoor is resolved from
linkedDoorOffset (read-before-write int id, D123 pattern). Folded
into the converter write-audit.

M-16 probes reverted; d125_check.py kept as the offline regression guard.
Generalisable quirk added to PORT-LEARNINGS.md §C.

tools_pc/d125_check.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+"""D125 diagnostic: does the propDefs blob in the *emitted* pccg sidecar
+(after RZ round-trip) byte-match tools_pc/d88_propdefs.convert_stream()?
+
+Tests the M-14 claim that the RAM propDefs is "zeros/garbage after record 0".
+If this script says MATCH, the corruption is downstream of the sidecar
+(runtime rebase / bank alloc / sizepropdef walk); if MISMATCH, it is in
+d88_emit.py's emit/placement or the RZ recompress.
+"""
+import csv, struct, zlib, sys
+from d88_propdefs import convert_stream, PROPDEF_PC_BYTES
+
+REGION = "ntsc-final"
+rom = open(f"data/ge007.{REGION}.z64", "rb").read()
+fl = {}
+for r in csv.reader(open("scripts/filelist.u.csv")):
+    if len(r) >= 3 and r[2]:
+        b = r[2].rsplit("/", 1)[-1]
+        b = b[:-4] if b.endswith(".bin") else b
+        fl[b] = (int(r[0]), int(r[1]))
+
+man = {}
+for r in csv.reader(open(f"data/pccg-{REGION}/manifest.csv")):
+    if r and r[0].startswith("Usetup"):
+        man[r[0]] = (int(r[1]), int(r[2]))
+sidebin = open(f"data/pccg-{REGION}/pccg.bin", "rb").read()
+
+be = lambda b, o: struct.unpack_from(">I", b, o)[0]
+targets = sys.argv[1:] or sorted(man)
+for nm in targets:
+    a, s = fl[nm]
+    dec_n64 = zlib.decompress(rom[a:a + s][2:], -15)
+    pd_n64, intro_n64 = be(dec_n64, 12), be(dec_n64, 8)
+    want, n64len, pclen = convert_stream(dec_n64, pd_n64, intro_n64)
+
+    off, size = man[nm]
+    dec_pc = zlib.decompress(sidebin[off:off + size][2:], -15)
+    # PC header: 8-byte slots, low 4 = LE offset
+    pd_pc = struct.unpack_from("<I", dec_pc, 8 * 3)[0]      # propDefs = field 3
+    intro_pc = struct.unpack_from("<I", dec_pc, 8 * 2)[0]   # intro = field 2
+    got = dec_pc[pd_pc:pd_pc + len(want)]
+
+    if got == want:
+        print(f"MATCH    {nm:18} pd@{pd_pc:#x} len={len(want)}")
+    else:
+        # first differing byte + which record it lands in
+        d = next((i for i in range(min(len(got), len(want))) if got[i] != want[i]), None)
+        rec, o = 0, 0
+        while o < (d or 0):
+            t = want[o + 3]
+            o += PROPDEF_PC_BYTES.get(t, 4)
+            rec += 1
+        print(f"MISMATCH {nm:18} pd@{pd_pc:#x} want={len(want)} got={len(got)} "
+              f"first diff @+{d} (~record {rec}, off {o:#x}); "
+              f"gotlen_vs_intro: {intro_pc - pd_pc} vs pclen {pclen}")

tools_pc/d88_emit.py

@@ -371,7 +371,10 @@ def convert_usetup(name, src):
         out[dst_o + 0x2c:dst_o + 0x30] = b"\x00\x00\x00\x00"
         # stan: dead-on-load (init_pathtable_something always sets it before
         # use, D88 same class as D79) -- zero it, never read from file.
-        out[dst_o + 0x30:dst_o + 0x38] = b"\x00\x00\x00\x00"
+        # NOTE: this slice is 8 bytes wide (widened stan ptr); the RHS MUST be
+        # 8 NUL bytes -- a 4-byte literal here makes `out` SHRINK by 4 per pad
+        # via Python slice-assign semantics, drifting every later region (D125).
+        out[dst_o + 0x30:dst_o + 0x38] = b"\x00\x00\x00\x00\x00\x00\x00\x00"
         if has_bbox:
             for k in range(6):
                 v = be32(src, src_o + 0x2c + 4 * k)