Phase 3f: lighting from wire normals; defuse shipped-in debug crash

Lighting: stride-8/9 vertices carry a normal (floats 3-5, uv at 6-7). The
backend transforms normals by the instance rotation and lights with a single
directional sun (GL_LIGHT0, smooth, two-sided, GL_COLOR_MATERIAL). Terrain
and hulls shade instead of reading flat.

LOD: the lod flush has no switch distances -- the host keeps the active LOD
at the child-list head and re-orders over the wire, so children[0] is right
and LOD changes come through as the sim runs.

The crash that halted the game once the RIO drove the sim was not ours: fault
at 0047E1D1 writing 0xFFFFFFFF is the RIO driver's DISABLE_AND_DIE debug
macro (PCSPAK.ASM, DIE_ON_ERROR=1), which deliberately faults on a serial-tx
anomaly -- error 3 = body char >0x7F during a RIO packet, i.e. a glitch on a
board reset. Release build (DIE_ON_ERROR=0) compiles it out and recovers
(and al,07Fh). patch_btl4opt.py NOPs all 12 sites by signature (with .orig
backup) = release behavior; game then survives RIO resets (1200+ frames).
(ALPHA_1 is git-ignored, so the tool ships, not the patched binary.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

emulator/patch_btl4opt.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+"""Neutralize the shipped-in debug crash macros in BTL4OPT.EXE.
+
+The Rel 4.10 BattleTech binary was built with the RIO serial driver's
+`DIE_ON_ERROR equ 1` diagnostic enabled (CODE/RP/MUNGA_L4/PCSPAK.ASM). Its
+`DISABLE_AND_DIE` macro deliberately faults ("crash loudly to the debugger")
+on any serial-transmit anomaly:
+
+    push eax; push edx
+    mov edx, 0FFFFFFFFh      ; crash loudly
+    mov eax, <error-code>
+    mov [edx], eax           ; write to 0xFFFFFFFF -> Exception 0E
+
+On the real pod a clean cockpit harness never tripped these; through the
+DOSBox-X serial passthrough a RIO glitch (e.g. during a board reset) hits
+error 3 (PCSPAK.ASM:1630, "body char > 0x7F") and halts the whole game. The
+release build (`DIE_ON_ERROR equ 0`) compiles the macro to nothing and lets
+the normal recovery path (`and al,07Fh`) continue.
+
+This tool finds every DISABLE_AND_DIE site by its exact 14-byte signature and
+replaces it with NOPs -- exactly the release-build behavior -- writing a
+<name>.orig backup first. Idempotent.
+
+Usage: patch_btl4opt.py <path-to-BTL4OPT.EXE>
+"""
+import re
+import sys
+
+SIG = re.compile(
+    rb'\x50\x52\xBA\xFF\xFF\xFF\xFF\xB8(.)\x00\x00\x00\x89\x02', re.DOTALL)
+
+
+def main():
+    if len(sys.argv) != 2:
+        raise SystemExit(__doc__)
+    path = sys.argv[1]
+    data = bytearray(open(path, 'rb').read())
+    sites = list(SIG.finditer(bytes(data)))
+    if not sites:
+        print("no DISABLE_AND_DIE sites found (already patched?)")
+        return
+    import os
+    bak = path + '.orig'
+    if not os.path.exists(bak):
+        open(bak, 'wb').write(data)
+        print(f"backup written: {bak}")
+    for m in sites:
+        code = m.group(1)[0]
+        va = 0x401000 + m.start() - 0xe00   # CODE VA 0x401000 @ file 0xe00
+        print(f"  NOP  VA 0x{va:06x}  (error code {code})")
+        data[m.start():m.end()] = b'\x90' * (m.end() - m.start())
+    open(path, 'wb').write(data)
+    print(f"patched {len(sites)} sites")
+
+
+if __name__ == "__main__":
+    main()