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_xref.py

@@ -0,0 +1,64 @@
+"""Find how instructions reference string offsets, and inspect 0x71 operands
+in context. Uses T3 jump-target values as confirmed instruction starts.
+"""
+import struct
+from pathlib import Path
+from collections import Counter
+
+ROOT = Path(__file__).resolve().parents[2] / "extracted" / "DATA1"
+
+def parse(name):
+    data = (ROOT / name).read_bytes()
+    f = struct.unpack_from("<13I", data, 8)
+    body = data[0x3C:]
+    n = len(body) // 4
+    dws = struct.unpack_from(f"<{n}I", body, 0)
+    return f, dws, body
+
+def decode_str(body, i):
+    raw = bytearray()
+    n = len(body) // 4
+    for j in range(i, min(i + 60, n)):
+        chunk = bytes(b ^ 0xFF for b in body[j*4:(j+1)*4])
+        raw += chunk
+        if 0 in chunk:
+            break
+    try:
+        return bytes(raw).split(b"\0")[0].decode("cp932")
+    except UnicodeDecodeError:
+        return None
+
+def xref(name, targets):
+    f, dws, body = parse(name)
+    print(f"\n=== {name}: xrefs to {[hex(t) for t in targets]} ===")
+    for t in targets:
+        hits = [i for i, v in enumerate(dws[:f[8]]) if v == t]
+        for i in hits:
+            lo = max(0, i - 6)
+            ctx = " ".join(f"{v:x}" for v in dws[lo:i + 3])
+            print(f"  {t:#x} referenced at [{i:#x}]: ...{ctx}...")
+
+def sample_71(name, k=6):
+    f, dws, body = parse(name)
+    print(f"\n=== {name}: T1 (0x71) operands in context ===")
+    off, cnt = f[8], f[7]
+    for e in list(dws[off:off + cnt])[:k]:
+        lo = max(0, e - 8)
+        ctx = " ".join(f"{v:x}" for v in dws[lo:e + 4])
+        print(f"  target [{e:#x}]: ...{ctx}...")
+
+def first_instrs(name, count=20):
+    """Dump first N dwords raw, plus known instruction starts from T3 values."""
+    f, dws, body = parse(name)
+    starts = sorted(set(dws[f[12]:f[12] + f[11]]))
+    print(f"\n=== {name}: first dwords ===")
+    print("  " + " ".join(f"{v:x}" for v in dws[:count]))
+    print(f"  T3-confirmed instruction starts (first 12): {[hex(s) for s in starts[:12]]}")
+
+if __name__ == "__main__":
+    xref("MENU.BIN", [0x303, 0x30B, 0x30E])
+    xref("SC0030.BIN", [0xEF80, 0xEF89, 0xEF91])
+    sample_71("SC0030.BIN")
+    sample_71("MENU.BIN", k=2)
+    first_instrs("MENU.BIN")
+    first_instrs("SC0030.BIN")