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/probe_header.py

@@ -0,0 +1,69 @@
+"""Probe SYS4 script headers across the DATA1 corpus.
+
+Header hypothesis (offsets in bytes):
+  0x00  char magic[8]      "SYS4422 "
+  0x08  u32 F0..F12        13 fields
+  0x3C  body (dword stream)
+
+Tests invariants and prints field stats.
+"""
+import struct
+import sys
+from pathlib import Path
+from collections import Counter
+
+ROOT = Path(__file__).resolve().parents[2] / "extracted" / "DATA1"
+
+def parse(path):
+    data = path.read_bytes()
+    magic = data[:8]
+    fields = struct.unpack_from("<13I", data, 8)
+    return data, magic, fields
+
+def main():
+    files = sorted(ROOT.glob("*.BIN"))
+    print(f"files: {len(files)}")
+
+    magics = Counter()
+    distinct = [Counter() for _ in range(13)]
+    fail_f12 = []      # F12 != filedwords - 15
+    fail_f6 = []       # F6 != 0x1C
+    fail_f11 = []      # F11 != 0
+    rel_a = Counter()  # F8 + F9 vs F12
+    rel_b = Counter()  # F10 + F11 vs F12
+    body_first = Counter()
+
+    for p in files:
+        data, magic, f = parse(p)
+        magics[magic] += 1
+        nd = len(data) // 4
+        for i, v in enumerate(f):
+            distinct[i][v] += 1
+        if f[12] != nd - 15:
+            fail_f12.append((p.name, f[12], nd - 15))
+        if f[6] != 0x1C:
+            fail_f6.append((p.name, f[6]))
+        if f[11] != 0:
+            fail_f11.append((p.name, f[10], f[11], f[12]))
+        rel_a["F8+F9==F12" if f[8] + f[9] == f[12] else
+              ("F8+F9<F12" if f[8] + f[9] < f[12] else "F8+F9>F12")] += 1
+        rel_b["F10+F11==F12" if f[10] + f[11] == f[12] else
+              ("F10+F11<F12" if f[10] + f[11] < f[12] else "F10+F11>F12")] += 1
+        if len(data) >= 0x40:
+            body_first[struct.unpack_from("<I", data, 0x3C)[0]] += 1
+
+    print("magics:", dict(magics))
+    print("\nfield value diversity (distinct count; top values):")
+    for i, c in enumerate(distinct):
+        top = ", ".join(f"{v:#x}x{n}" for v, n in c.most_common(4))
+        print(f"  F{i:<2} @0x{8+i*4:02X}: {len(c):4} distinct | {top}")
+    print(f"\nF6==0x1C fails: {len(fail_f6)} {fail_f6[:5]}")
+    print(f"F12==dwords-15 fails: {len(fail_f12)} {fail_f12[:5]}")
+    print(f"F11!=0 count: {len(fail_f11)} {fail_f11[:5]}")
+    print("rel F8+F9 vs F12:", dict(rel_a))
+    print("rel F10+F11 vs F12:", dict(rel_b))
+    print("\nfirst body dword (top 15):",
+          ", ".join(f"{v:#x}x{n}" for v, n in body_first.most_common(15)))
+
+if __name__ == "__main__":
+    main()