chore: initialize age-reimpl repo

Reverse-engineering + open reimplementation workspace for Eushully's AGE/SYS4
engine (first target: Himegari). The repo root is age-reimpl/; the original game
install and the extracted ALF data are siblings outside the repo and are never
tracked. build/ (derived corpora) is gitignored and regenerated by the tools.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/validate_opcode_table.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Definitive test: replicate Kelebek's data_array_end shrinking (stop code at first
+string/array offset), then measure clean decode rate over all Himegari scripts."""
+import os, re, sys, collections
+from pathlib import Path
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+import paths
+import sys4load
+
+CPP=paths.KELEBEK_CPP.read_text(encoding="utf-8")
+TABLE={}; LABEL={}
+for m in re.finditer(r'\{\s*(0x[0-9A-Fa-f]+)\s*,\s*"([^"]*)"\s*,\s*(0x[0-9A-Fa-f]+)\s*\}', CPP):
+    TABLE[int(m.group(1),16)]=int(m.group(3),16); LABEL[int(m.group(1),16)]=m.group(2)
+
+files=paths.scripts()
+
+clean=dirty=0; parsefail=0
+still_unknown=collections.Counter(); examples={}
+instr_total=0
+for name,p in sorted(files.items()):
+    try: scr=sys4load.load(p)
+    except Exception: parsefail+=1; continue
+    dw=scr.dwords; cl=scr.code_len
+    end=cl                     # data_array_end, starts at F8, shrinks to first string/array off
+    i=0; ok=True; reason=""
+    n_instr=0
+    while i<end:
+        op=dw[i]
+        if op not in TABLE:
+            ok=False; reason=f"unknown 0x{op:x}@{i}"
+            if op<0x1000: still_unknown[op]+=1; examples.setdefault(op,name)
+            break
+        argc=TABLE[op]
+        base=i+1
+        if base+2*argc>end:
+            ok=False; reason=f"overrun 0x{op:x}@{i}"; break
+        for a in range(argc):
+            atype=dw[base+2*a]; aval=dw[base+2*a+1]
+            if atype==2 and 0<=aval<end:      # inline string -> shrink code end
+                end=min(end,aval)
+            if op==0x64 and a==1 and 0<=aval<end:  # copy-local-array footer ref
+                end=min(end,aval)
+        i=base+2*argc; n_instr+=1
+    if ok and i==end:
+        clean+=1; instr_total+=n_instr
+    else:
+        dirty+=1
+        if len(examples)<20 and reason: pass
+
+print(f"scripts: {len(files)}  parsefail(container): {parsefail}")
+print(f"CLEAN decode (Kelebek table + string-pool boundary): {clean}")
+print(f"DIRTY: {dirty}")
+print(f"total instructions decoded in clean files: {instr_total}")
+print(f"\nremaining small unknown opcodes (genuine gaps):")
+for op,c in still_unknown.most_common():
+    print(f"  0x{op:x}  files={c}  e.g. {examples.get(op)}  known={op in TABLE}")
+if not still_unknown:
+    print("  (none)")