re: an embedded .prt part is a top-level RATC bundle, addressed by its element prefix

Read first: ui-rat-layout.md OWNS the RATC stack and already documents
the 60-byte element declaration table and 'one bundle = one
(context x language) build of that screen'.  What it does not say is how
a part is addressed when it is NOT a pak entry.

The elements of one bundle share a common name prefix, and that prefix
is the part name.  GP_MAIN_GAME_E2D.pak has 130 bundles with 114
distinct element prefixes -- pgmenu_btn00, pghud_wing, pgface,
pghud_range, pgmanuva_eff0 -- exactly the in-game part names.

The 100 in-game-only .prt names match a 2D bundle prefix 68 times; the
control, the 241 shipped parts, matches ZERO.  The two families are
disjoint on the test.  13 shipped parts match a bundle prefix in their
own screen pak, which is the expected shape.

Four of the five mission banners land here: pgmsg_start.prt is E2D
bundle 0x89fac252, a one-element bundle declaring pgmsg_start_sub.rat;
likewise _end_, _failed_, _restart_.  pgmsg_update has no bundle at all,
consistent with having no _sub.rat.

32 in-game names still have no 2D bundle.  They cluster into families
whose base name is a bundle, reading as a variant declared inside a
parent bundle -- a reading, not adopted.

Artefact +38 lines / 0 deletions; the other six regenerate
byte-identical.

tools/re-capture/prt_parts.py

@@ -3,7 +3,7 @@
 
 Regenerates docs/re/data/prt-parts.txt.
 """
-import sys, os, glob, re, collections
+import sys, os, glob, re, struct, collections
 
 HERE = os.path.dirname(os.path.abspath(__file__))
 sys.path.insert(0, HERE)
@@ -15,10 +15,21 @@ FIVE = ['pgmsg_start.prt', 'pgmsg_end.prt', 'pgmsg_update.prt',
 PRE = ['', 'Stage\\', 'stage\\', 'message\\', 'language\\', '2d\\', 'ui\\', 'prt\\',
        'view\\'] + [l + '\\' for l in ('eng', 'jpn', 'fra', 'deu', 'ita', 'esp')]
 
+def _elements(b):
+    n = struct.unpack_from('>I', b, 0x14)[0]
+    if not (0 < n < 4000) or 0x20 + n * 60 > len(b):
+        return []
+    return [b[0x20 + i * 60:0x20 + i * 60 + 28].split(b'\x00')[0].decode('latin-1', 'replace')
+            for i in range(n)]
+
+def _stem(e):
+    return re.sub(r'\.(t32|rat|prm)$', '', e)
+
 def main():
     H = collections.defaultdict(set)
     names = set()
     ref = collections.defaultdict(set)
+    pref2d, prefall = set(), set()
     rat = collections.defaultdict(set)
     for pk in sorted(glob.glob('/work/sylph_extract/**/*.pak', recursive=True)):
         base = os.path.basename(pk)
@@ -29,6 +40,13 @@ def main():
             if b[:4] == b'RATC':
                 for m in re.finditer(rb'[A-Za-z0-9_]{3,40}_sub\.rat', b):
                     rat[m.group(0).decode()].add(base)
+                e = _elements(b)
+                if e:
+                    pfx = os.path.commonprefix([_stem(x) for x in e]).rstrip('_')
+                    if pfx:
+                        prefall.add(pfx)
+                        if '2D.pak' in base:
+                            pref2d.add(pfx)
 
     print("# Where `.prt` screen parts live")
     print("# Regenerate: python3 tools/re-capture/prt_parts.py")
@@ -68,6 +86,20 @@ def main():
     print("   pg* parts: %d, of which %d resolve: %s"
           % (len(pg), sum(1 for n in pg if res[n]), sorted(n for n in pg if res[n])))
 
+    ing = [n for n in names if not res[n] and 'tables.pak' not in ref[n]]
+    sh = [n for n in names if res[n]]
+    match = lambda ns, S: sum(1 for n in ns if n[:-4] in S or n[:-4] + '_sub' in S)
+    print("\n## AN EMBEDDED PART IS A TOP-LEVEL RATC BUNDLE, named by its element prefix")
+    print("   RATC bundle element-prefixes: %d distinct (2D paks: %d)" % (len(prefall), len(pref2d)))
+    print("   in-game-only .prt (%d): match a 2D bundle prefix %d ; any bundle prefix %d"
+          % (len(ing), match(ing, pref2d), match(ing, prefall)))
+    print("   CONTROL shipped .prt (%d): match a 2D bundle prefix %d ; any bundle prefix %d"
+          % (len(sh), match(sh, pref2d), match(sh, prefall)))
+    resid = sorted(n for n in ing if n[:-4] not in pref2d and n[:-4] + '_sub' not in pref2d)
+    print("   in-game .prt with NO 2D bundle (%d):" % len(resid))
+    for n in resid:
+        print("        %s" % n)
+
     print("\n## `<stem>_sub.rat` sub-bundles inside RATC")
     print("   distinct _sub.rat names: %d" % len(rat))
     for k in sorted(rat):