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_leads.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+"""Corpus-wide candidate-opcode histogram.
+
+T3 entries point at [0x8F, 0, line#] records embedded in CODE. The dword right
+after each 3-dword T3 record is the lead of the next statement -> candidate
+opcode. Histogram those leads over all root-override + DATA1 scripts.
+Also: histogram the dword immediately preceding each `0x02 <off>` string ref
+(candidate "takes-a-string" opcodes), with example files.
+"""
+import os, sys, collections
+from pathlib import Path
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+import paths
+import sys4load
+
+# authoritative set: game-dir overrides shadow extracted/DATA1
+files = paths.scripts()
+print(f"{len(files)} scripts (overrides win)")
+
+lead_hist = collections.Counter()          # dword after each T3 record
+lead_examples = collections.defaultdict(set)
+pre_str = collections.Counter()            # dword before each 0x02 <off> ref
+pre_str_ex = collections.defaultdict(set)
+first_dword = collections.Counter()
+t3_rec_shape_ok = 0
+t3_rec_total = 0
+bad = 0
+
+for name, p in sorted(files.items()):
+    try:
+        scr = sys4load.load(p)
+    except Exception as e:
+        bad += 1
+        continue
+    dw = scr.dwords
+    code_len = scr.code_len
+    first_dword[dw[0]] += 1
+    # statement leads via T3 records
+    for e in scr.table_entries("T3"):
+        if not (0 <= e < code_len):
+            continue
+        t3_rec_total += 1
+        if e + 2 < code_len and dw[e] == 0x8F and dw[e+1] == 0:
+            t3_rec_shape_ok += 1
+            nxt = e + 3
+            if nxt < code_len:
+                v = dw[nxt]
+                lead_hist[v] += 1
+                if len(lead_examples[v]) < 3:
+                    lead_examples[v].add(name)
+    # dword preceding string refs (ref index i+1 holds offset; tag at i)
+    for ref_idx in scr.string_refs:          # ref_idx points at the offset dword
+        tag_idx = ref_idx - 1                # the 0x02
+        if tag_idx - 1 >= 0:
+            v = dw[tag_idx - 1]
+            pre_str[v] += 1
+            if len(pre_str_ex[v]) < 3:
+                pre_str_ex[v].add(name)
+
+print(f"parse failures: {bad}")
+print(f"T3 records with shape [0x8F,0,*]: {t3_rec_shape_ok}/{t3_rec_total}")
+print("\n== first body dword ==")
+for v, c in first_dword.most_common(8):
+    print(f"  {v:#06x}  {c}")
+print(f"\n== statement leads after T3 records (top 40 of {len(lead_hist)}) ==")
+total = sum(lead_hist.values())
+for v, c in lead_hist.most_common(40):
+    ex = ",".join(sorted(lead_examples[v]))
+    print(f"  {v:#06x}  {c:>7} ({100*c/total:5.2f}%)  e.g. {ex}")
+print(f"\n== dword preceding `0x02 <off>` string refs (top 25 of {len(pre_str)}) ==")
+tot2 = sum(pre_str.values())
+for v, c in pre_str.most_common(25):
+    ex = ",".join(sorted(pre_str_ex[v]))
+    print(f"  {v:#06x}  {c:>7} ({100*c/tot2:5.2f}%)  e.g. {ex}")