Fix table lookup for equal-strength material configs

PieceConfig canonicalizes side ordering by total strength (stronger
side -> White), but only swapped when bs > ws, leaving the bs == ws
case with no tiebreak. For equal-strength asymmetric material (e.g.
KQP vs KRR, both 1000), the canonical orientation then depended on
which color held which pieces on the probed board, so cfg.name()
produced "KQPKRR" or "KRRKQP" depending on the input.

Since tables are opened by cfg.name(), half the orientations of every
such material computed a filename that doesn't exist on disk and
probing wrongly reported table-not-found.

Add a deterministic tiebreak mirroring Piece_Config::sort_pieces in
the C++ generator: when totals are equal, the side with more
high-value pieces (more queens, then rooks, ...) becomes White, so
cfg.name() reproduces the generator's on-disk filename.

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

Author: noobpwnftw

chess/chesstb.py

@@ -146,6 +146,18 @@ def material_key_of(pieces: List[Tuple[int, int]]) -> int:
 _TYPE_ORDER = {KING: 0, QUEEN: 1, ROOK: 2, BISHOP: 3, KNIGHT: 4, PAWN: 5}
 
 
+def _composition_key(pieces: List[Tuple[int, int]], color: int) -> List[int]:
+    """Per-type piece counts for `color`, indexed by C++ type code so that
+    lexicographic comparison orders by KING, QUEEN, ROOK, BISHOP, KNIGHT, PAWN.
+    Mirrors the ``std::array<int8_t, PIECE_TYPE_NB>`` tiebreak key in
+    ``Piece_Config::sort_pieces`` (src/chess/piece_config.cpp)."""
+    counts = [0] * (PAWN + 1)
+    for c, t in pieces:
+        if c == color:
+            counts[t] += 1
+    return counts
+
+
 class PieceConfig:
     """Canonical material config. `pieces` is a list of (cpp_color, type)."""
 
@@ -154,7 +166,10 @@ def __init__(self, pieces: List[Tuple[int, int]]):
         # Input may be in any orientation; we canonicalize.
         ws = sum(_STRENGTH[t] for c, t in pieces if c == CPP_WHITE)
         bs = sum(_STRENGTH[t] for c, t in pieces if c == CPP_BLACK)
-        if bs > ws:
+        swap = bs > ws
+        if bs == ws:
+            swap = _composition_key(pieces, CPP_BLACK) > _composition_key(pieces, CPP_WHITE)
+        if swap:
             pieces = [(CPP_BLACK if c == CPP_WHITE else CPP_WHITE, t) for c, t in pieces]
         # sort: white side first then black; within side by type order.
         pieces = sorted(pieces, key=lambda ct: (ct[0], _TYPE_ORDER[ct[1]]))