eval.c: defer B/N/R mobility scoring near enemy king, queen king-adjacency fix, FLIP() -> precomputed xColor

Bishop/knight/rook mobility computed during their own eval pass only
sees enemy pawn (B/N) or pawn+minor (R) attacks -- a square right next
to the enemy king looks "safe" and counts toward mobility even though
it plainly isn't (e.g. a pawn push cutting off a bishop's retreat onto
squares next to the enemy king). Below EVAL_MOBILITY_CAREFULLY_BELOW
(3) candidate squares, defer scoring to _EvalTrappedPieces, which
re-derives the true safe-escape count once every piece type -- the
enemy king included -- has contributed to the attack tables. Genuinely
0-mobility pieces are scored immediately instead: more attack info can
only shrink an already-empty set, so there's nothing to gain by
waiting.

Queen doesn't need deferral (its own eval pass runs after every
smaller piece type, so it already has complete information) -- instead
bbUnsafeForQueen now also excludes squares adjacent to the enemy king
unless we already defend them.

Also: precompute xColor = FLIP(uColor) once per function/loop
iteration everywhere eval.c could hit FLIP() more than once evaluating
it, instead of recomputing it at each use site.

Verified: precommit_check.sh (self-test + DEBUG smoke test) clean.
Curated ECM suites at sd10 vs head_reference: ecm_ringers 4/11 (was
3/11), ecm_confident_quick 70/90 (flat), ecm_hard_quick 19/90 (was
18/90) -- no regressions. Overnight self-play SPRT trending positive
(370 games, llr=+0.20).

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 308 insertions, 122 deletions

diff --git a/src/eval.c b/src/eval.c
index 7d3f38b..e84470b 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -50,6 +50,18 @@ Revision History:
 #define CoorFromBitBoardRank1ToRank8 FastCoorFromBitBoardRank1ToRank8
 #endif // !CROUTINES
 
+// Bishop/knight/rook mobility computed during their own eval pass only
+// knows about enemy PAWN attacks (bishop/knight) or enemy PAWN+MINOR
+// attacks (rook) -- the only attack tables fully populated that early
+// -- so a square right next to the enemy king, or (for bishop/knight)
+// covered by an enemy piece not yet evaluated, looks "safe" and counts
+// toward mobility even though it plainly isn't. Below this many
+// candidate squares, don't trust that partial-information count: defer
+// to _EvalTrappedPieces, which re-derives a final safe-escape count
+// once the full attack picture (both colors, both kings) is in.
+// Genuinely 0-mobility pieces are the one exception -- see
+// _EvalBishop's comment on why those are scored immediately instead.
+#define EVAL_MOBILITY_CAREFULLY_BELOW (3)
 
 //
 // To simplify code / maintenance I use the same loop for both colors
@@ -1782,6 +1794,7 @@ Return value:
 **/
 {
     ULONG uColor;
+    ULONG xColor;
     ULONG u, v;
     COOR c;
     COOR cLeftmostPasser, cRightmostPasser;
@@ -1796,6 +1809,7 @@ Return value:
     FOREACH_COLOR(uColor)
     {
         ASSERT(IS_VALID_COLOR(uColor));
+        xColor = FLIP(uColor);
         if (pHash->bbPasserLocations[uColor])
         {
             ASSERT(FastCountBits(pos->bbPawns[uColor]) > 0);
@@ -1881,10 +1895,10 @@ Return value:
 #endif
             for (u = A; u <= D; u++)
             {
-                if (pHash->uCountPerFile[FLIP(uColor)][u + 1] != 0)
+                if (pHash->uCountPerFile[xColor][u + 1] != 0)
                 {
-                    ASSERT(pos->bbPawns[FLIP(uColor)] & BBFILE[u]);
-                    if (!(pHash->bbPasserLocations[FLIP(uColor)] & BBFILE[u]))
+                    ASSERT(pos->bbPawns[xColor] & BBFILE[u]);
+                    if (!(pHash->bbPasserLocations[xColor] & BBFILE[u]))
                     {
                         break;
                     }
@@ -1902,10 +1916,10 @@ Return value:
 
             for (u = H; u >= E; u--)
             {
-                if (pHash->uCountPerFile[FLIP(uColor)][u + 1] != 0)
+                if (pHash->uCountPerFile[xColor][u + 1] != 0)
                 {
-                    ASSERT(pos->bbPawns[FLIP(uColor)] & BBFILE[u]);
-                    if (!(pHash->bbPasserLocations[FLIP(uColor)] & BBFILE[u]))
+                    ASSERT(pos->bbPawns[xColor] & BBFILE[u]);
+                    if (!(pHash->bbPasserLocations[xColor] & BBFILE[u]))
                     {
                         break;
                     }
@@ -2017,6 +2031,8 @@ Return value:
 
 **/
 {
+    ULONG xColor = FLIP(uColor);
+
     if (0 == pHash->uCountPerFile[uColor][uPawnFile + 1])
     {
         return FALSE;                 // no friendly pawn on that file at all
@@ -2049,7 +2065,7 @@ Return value:
         {
             BITBOARD bbDestination = (uColor == WHITE) ?
                 (bbHelper >> 8) : (bbHelper << 8);
-            if ((bbDestination & pos->bbPawnAttacks[FLIP(uColor)]) &&
+            if ((bbDestination & pos->bbPawnAttacks[xColor]) &&
                 !(bbDestination & pos->bbPawnAttacks[uColor]))
             {
                 return FALSE;
@@ -2062,7 +2078,7 @@ Return value:
     // enemy pawn on this same file already sits at c's rank or behind
     // it (from our own forward direction), permanently blocking the
     // way.
-    return (0 == (pos->bbPawns[FLIP(uColor)] & BBFILE[uPawnFile] & bbBlockingRanks));
+    return (0 == (pos->bbPawns[xColor] & BBFILE[uPawnFile] & bbBlockingRanks));
 }
 
 
@@ -4065,23 +4081,29 @@ Return value:
 static void
 _RecordTrappedCandidate(IN OUT POSITION *pos,
                          IN ULONG uColor,
-                         IN COOR c)
+                         IN COOR c,
+                         IN BITBOARD bbEscapes)
 /**
 
 Routine description:
 
-    Record a zero-mobility piece as a trapped-piece candidate for
-    uColor. Used by _EvalBishop/_EvalKnight/_EvalRook/_EvalQueen; the
-    actual attacked-or-not check happens later, in
-    _EvalTrappedPieces. Capped at ARRAY_LENGTH(pos->cTrapped[0])
-    candidates per side -- extras are just dropped, not a real concern
-    in practice.
+    Record a trapped-piece candidate for uColor -- either a genuinely
+    zero-mobility piece (bbEscapes passed as 0: nothing to re-derive,
+    see _EvalBishop's comment), or a bishop/knight deferred because its
+    own partial-information mobility count was low but nonzero
+    (bbEscapes is that piece's own bbMobility snapshot at nomination
+    time). Used by _EvalBishop/_EvalKnight/_EvalRook/_EvalQueen; the
+    actual attacked-or-not check, and (for a deferred candidate) the
+    final mobility re-derivation, happen later in _EvalTrappedPieces.
+    Capped at ARRAY_LENGTH(pos->cTrapped[0]) candidates per side --
+    extras are just dropped, not a real concern in practice.
 
 Parameters:
 
     POSITION *pos,
     ULONG uColor,
-    COOR c
+    COOR c,
+    BITBOARD bbEscapes
 
 Return value:
 
@@ -4091,6 +4113,7 @@ Return value:
 {
     if (pos->uNumTrapped[uColor] < ARRAY_LENGTH(pos->cTrapped[uColor]))
     {
+        pos->bbTrappedEscapes[uColor][pos->uNumTrapped[uColor]] = bbEscapes;
         pos->cTrapped[uColor][pos->uNumTrapped[uColor]++] = c;
     }
 }
@@ -4201,19 +4224,6 @@ Return value:
               "good/bad transient pawns");
 
     //
-    // Removed 2026-08-30: BISHOP_IN_CLOSED_POSITION[pos->uClosedScaler]
-    // duplicated bishop mobility (computed just below) rather than
-    // adding a distinct angle on it. uClosedScaler is a coarse,
-    // whole-board openness proxy for exactly the same fact bishop
-    // mobility measures directly and per-bishop via ray-casting -- how
-    // much this specific bishop's diagonals are blocked by pawns. The
-    // mobility term is strictly more precise (opposite-bishop-color
-    // endgames are the clearest case where "position is open overall"
-    // and "this bishop's diagonal is blocked" diverge), so cut the
-    // redundant whole-board proxy rather than scale it down.
-    //
-
-    //
     // Bishop mobility (and update attack tables) -- board_representation/
     // EVAL.md section 1b: _BishopAttacksBB(c, pos->bbOccupied)
     // (generate.c's magic-bitboard slider lookup, already used by move
@@ -4310,20 +4320,51 @@ Return value:
     uTotalMobility = CountBits(bbMobility);
 
     ASSERT(uTotalMobility <= 13);
-    EVAL_TERM(uColor,
-              BISHOP,
-              c,
-              pos->iScore[uColor],
-              BISHOP_MOBILITY_BY_SQUARES[uTotalMobility],
-              "bishop mobility");
 
     //
-    // Look for bishops with no mobility, they are trapped and, later,
-    // we'll see if they are also under attack too.
+    // uTotalMobility here is necessarily pessimistic-as-an-upper-bound
+    // (not pessimistic-as-a-lower-bound): at this point in Eval() only
+    // enemy PAWN attacks are known, so a square next to the enemy king,
+    // or covered by an enemy piece that hasn't run its own eval pass
+    // yet, still looks safe and gets counted. More attack information
+    // can only mark MORE squares unsafe later, never fewer -- so this
+    // count can only ever be too high, never too low.
     //
-    if (uTotalMobility == 0)
+    // That asymmetry is exactly why a genuinely 0-mobility bishop is
+    // scored and recorded immediately rather than deferred: 0 is
+    // already the floor, so a fuller attack picture later can't change
+    // it (0 minus more unsafe squares is still 0) -- there is nothing
+    // to gain by waiting. A LOW but nonzero count, however, could
+    // easily still be an overcount (the classic case that motivated
+    // this: a pawn push that cuts off the bishop's retreat leaves two
+    // "safe" squares right next to the enemy king that are only safe
+    // because the king's own attacks aren't in the table yet) -- defer
+    // those to _EvalTrappedPieces, which re-derives the true count once
+    // both kings and every piece type have contributed to the attack
+    // tables, instead of locking in a score that a fuller picture might
+    // revise downward.
+    //
+    if (uTotalMobility < EVAL_MOBILITY_CAREFULLY_BELOW)
     {
-        _RecordTrappedCandidate(pos, uColor, c);
+        if (uTotalMobility == 0)
+        {
+            EVAL_TERM(uColor,
+                      BISHOP,
+                      c,
+                      pos->iScore[uColor],
+                      BISHOP_MOBILITY_BY_SQUARES[0],
+                      "bishop mobility");
+        }
+        _RecordTrappedCandidate(pos, uColor, c, bbMobility);
+    }
+    else // reasonable mobility
+    {
+        EVAL_TERM(uColor,
+                  BISHOP,
+                  c,
+                  pos->iScore[uColor],
+                  BISHOP_MOBILITY_BY_SQUARES[uTotalMobility],
+                  "bishop mobility");
     }
 
     //
@@ -4391,6 +4432,7 @@ Return value:
     ULONG xColor;
     ULONG uPawnsSupporting;
     ULONG uMobilitySquares;
+    BITBOARD bbMobility;
     SCORE i;
     ULONG uDist;
 
@@ -4542,7 +4584,6 @@ Return value:
         BITBOARD bbEnemyNonPawnOcc = _BuildFriendlySideBB(pos, xColor) &
                                       ~pos->bbPawns[xColor];
         BITBOARD bbUnsafeForMinor = pos->bbPawnAttacks[xColor];
-        BITBOARD bbMobility;
 
         pos->bbMinorAttacks[uColor] |= bbAttack;
 
@@ -4553,15 +4594,31 @@ Return value:
     }
     ASSERT(uMobilitySquares >= 0);
     ASSERT(uMobilitySquares <= 8);
-    EVAL_TERM(uColor,
-              KNIGHT,
-              c,
-              pos->iScore[uColor],
-              KNIGHT_MOBILITY_BY_COUNT[uMobilitySquares],
-              "knight mobility");
-    if (uMobilitySquares == 0)
+
+    // See _EvalBishop's comment above its own identically-structured
+    // mobility scoring for why 0-mobility is scored immediately while
+    // a low-but-nonzero count is deferred to _EvalTrappedPieces instead.
+    if (uMobilitySquares < EVAL_MOBILITY_CAREFULLY_BELOW)
     {
-        _RecordTrappedCandidate(pos, uColor, c);
+        if (uMobilitySquares == 0)
+        {
+            EVAL_TERM(uColor,
+                      KNIGHT,
+                      c,
+                      pos->iScore[uColor],
+                      KNIGHT_MOBILITY_BY_COUNT[0],
+                      "knight mobility");
+        }
+        _RecordTrappedCandidate(pos, uColor, c, bbMobility);
+    }
+    else // reasonable mobility
+    {
+        EVAL_TERM(uColor,
+                  KNIGHT,
+                  c,
+                  pos->iScore[uColor],
+                  KNIGHT_MOBILITY_BY_COUNT[uMobilitySquares],
+                  "knight mobility");
     }
 }
 
@@ -4588,6 +4645,7 @@ Return value:
     PIECE p;
     ULONG uColor;
     ULONG uTotalMobility;
+    BITBOARD bbMobility;
     COOR cSquare;
     SCORE i;
 
@@ -4640,7 +4698,7 @@ Return value:
               c,
               pos->iScore[uColor],
               ROOK_VALUE_AS_PAWNS_COME_OFF[FastCountBits(pos->bbPawns[uColor]) +
-                                           FastCountBits(pos->bbPawns[FLIP(uColor)])],
+                                           FastCountBits(pos->bbPawns[xColor])],
               "increase in value/pawns");
 
     //
@@ -4670,21 +4728,21 @@ Return value:
     //
     {
         BITBOARD bbAttack = _RookAttacksBB(c, pos->bbOccupied);
-        BITBOARD bbEnemyOcc = _BuildFriendlySideBB(pos, FLIP(uColor));
-        BITBOARD bbEnemySame = pos->bbPieces[FLIP(uColor)][ROOK];
-        BITBOARD bbEnemyGEContinue = pos->bbPieces[FLIP(uColor)][QUEEN] |
-                                       COOR_TO_BB(KingPosition(pos, FLIP(uColor)));
+        BITBOARD bbEnemyOcc = _BuildFriendlySideBB(pos, xColor);
+        BITBOARD bbEnemySame = pos->bbPieces[xColor][ROOK];
+        BITBOARD bbEnemyGEContinue = pos->bbPieces[xColor][QUEEN] |
+                                       COOR_TO_BB(KingPosition(pos, xColor));
         BITBOARD bbFriendRQ = pos->bbPieces[uColor][ROOK] |
                               pos->bbPieces[uColor][QUEEN];
-        BITBOARD bbUnsafeForRook = pos->bbPawnAttacks[FLIP(uColor)] |
-                                    pos->bbMinorAttacks[FLIP(uColor)];
+        BITBOARD bbUnsafeForRook = pos->bbPawnAttacks[xColor] |
+                                    pos->bbMinorAttacks[xColor];
         BITBOARD bbExclude = 0;
         BITBOARD bbSeen = 0;
         BITBOARD bbLayer = bbAttack;
-        BITBOARD bbMobility = 0;
         BITBOARD bbXrayAccum = 0;
         BITBOARD bbFirstLayerMask = 0;
 
+        bbMobility = 0;
         pos->bbRookAttacks[uColor] |= bbAttack;
 
         //
@@ -4769,57 +4827,74 @@ Return value:
         uTotalMobility = CountBits(bbMobility);
     }
     ASSERT(uTotalMobility <= 14);
+    ASSERT(pos->uArmyScaler[xColor] <= 31);
 
-    ASSERT(pos->uArmyScaler[FLIP(uColor)] <= 31);
-    i = ROOK_MOBILITY_BY_SQUARES[uTotalMobility];
-    i *= (int)(REDUCED_MATERIAL_UP_SCALER[pos->uArmyScaler[FLIP(uColor)]] + 1);
-    i /= 8;
-    EVAL_TERM(uColor,
-              ROOK,
-              c,
-              pos->iScore[uColor],
-              i,
-              "rook mobility");
-
-    if (uTotalMobility < 3)
+    // Same partial-information reasoning, and same immediate-0/deferred-
+    // low-nonzero split, as _EvalBishop's identically-structured
+    // mobility scoring (see its comment) -- bbUnsafeForRook above only
+    // knows about enemy pawn/minor attacks, not the enemy king's or (for
+    // a rook specifically) a not-yet-evaluated enemy queen's, so a low
+    // nonzero count here is still liable to be an overcount.
+    if (uTotalMobility < EVAL_MOBILITY_CAREFULLY_BELOW)
     {
-        // Look for rooks with no mobility who are under attack.  These
-        // pieces are trapped!
         if (uTotalMobility == 0)
         {
-            _RecordTrappedCandidate(pos, uColor, c);
+            i = ROOK_MOBILITY_BY_SQUARES[0];
+            i *= (int)(REDUCED_MATERIAL_UP_SCALER[pos->uArmyScaler[xColor]] + 1);
+            i /= 8;
+            EVAL_TERM(uColor,
+                      ROOK,
+                      c,
+                      pos->iScore[uColor],
+                      i,
+                      "rook mobility");
         }
+        _RecordTrappedCandidate(pos, uColor, c, bbMobility);
 
-        // Rook trapped in the corner by a stupid friendly king? --
-        // color-indexed instead of a WHITE/BLACK branch over two
-        // mirrored blocks (board_representation/EVAL.md section 9).
+        // Is the rook trapped in the corner by a stupid friendly
+        // king? -- purely geometric (unrelated to the mobility
+        // deferral above), still gated on the same coarse "cramped"
+        // raw-mobility threshold -- color-indexed instead of a
+        // WHITE/BLACK branch over two mirrored blocks
+        // (board_representation/EVAL.md section 9).
         ASSERT(IS_VALID_COLOR(uColor));
-        {
-            static const ULONG BACK_RANK_MASK[2] = { 0x00, 0x70 }; // BLACK, WHITE
-            static const COOR E_CORNER[2] = { E8, E1 };
-            static const COOR D_CORNER[2] = { D8, D1 };
+        ASSERT(IS_ON_BOARD(c));
 
-            ASSERT(IS_ON_BOARD(c));
-            if ((c & 0xF0) == BACK_RANK_MASK[uColor])
+        static const ULONG BACK_RANK_MASK[2] = { 0x00, 0x70 }; // BLACK, WHITE
+        static const COOR E_CORNER[2] = { E8, E1 };
+        static const COOR D_CORNER[2] = { D8, D1 };
+
+        if ((c & 0xF0) == BACK_RANK_MASK[uColor])
+        {
+            cSquare = KingPosition(pos, uColor);
+            ASSERT(IS_ON_BOARD(cSquare));
+            if ((cSquare & 0xF0) == BACK_RANK_MASK[uColor])
             {
-                cSquare = KingPosition(pos, uColor);
-                ASSERT(IS_ON_BOARD(cSquare));
-                if ((cSquare & 0xF0) == BACK_RANK_MASK[uColor])
+                if (((cSquare > E_CORNER[uColor]) && (c > cSquare)) ||
+                    ((cSquare < D_CORNER[uColor]) && (c < cSquare)))
                 {
-                    if (((cSquare > E_CORNER[uColor]) && (c > cSquare)) ||
-                        ((cSquare < D_CORNER[uColor]) && (c < cSquare)))
-                    {
-                        EVAL_TERM(uColor,
-                                  ROOK,
-                                  c,
-                                  pos->iScore[uColor],
-                                  KING_TRAPPING_ROOK,
-                                  "king trapping rook");
-                    }
+                    EVAL_TERM(uColor,
+                              ROOK,
+                              c,
+                              pos->iScore[uColor],
+                              KING_TRAPPING_ROOK,
+                              "king trapping rook");
                 }
             }
         }
-    } // if low mobility
+    }
+    else // reasonable mobility
+    {
+        i = ROOK_MOBILITY_BY_SQUARES[uTotalMobility];
+        i *= (int)(REDUCED_MATERIAL_UP_SCALER[pos->uArmyScaler[xColor]] + 1);
+        i /= 8;
+        EVAL_TERM(uColor,
+                  ROOK,
+                  c,
+                  pos->iScore[uColor],
+                  i,
+                  "rook mobility");
+    }
 }
 
 
@@ -4843,6 +4918,7 @@ Return value:
 {
     PIECE p = pos->rgSquare[c].pPiece;
     ULONG uColor;
+    ULONG xColor;
     ULONG uTotalMobility;
     ULONG u;
     COOR cKing;
@@ -4851,7 +4927,8 @@ Return value:
     ASSERT(p && IS_QUEEN(p));
     uColor = GET_COLOR(p);
     ASSERT(IS_VALID_COLOR(uColor));
-    cKing = KingPosition(pos, FLIP(uColor));
+    xColor = FLIP(uColor);
+    cKing = KingPosition(pos, xColor);
     ASSERT(IS_ON_BOARD(cKing));
     ASSERT(IS_KING(pos->rgSquare[cKing].pPiece));
 
@@ -4890,12 +4967,29 @@ Return value:
     // more), so the enemy side of each pass's continue-set is empty.
     //
     {
-        BITBOARD bbEnemyOcc = _BuildFriendlySideBB(pos, FLIP(uColor));
-        BITBOARD bbEnemyGE = pos->bbPieces[FLIP(uColor)][QUEEN] |
+        BITBOARD bbEnemyOcc = _BuildFriendlySideBB(pos, xColor);
+        BITBOARD bbEnemyGE = pos->bbPieces[xColor][QUEEN] |
                               COOR_TO_BB(cKing);
-        BITBOARD bbUnsafeForQueen = pos->bbPawnAttacks[FLIP(uColor)] |
-                                     pos->bbMinorAttacks[FLIP(uColor)] |
-                                     pos->bbRookAttacks[FLIP(uColor)];
+        //
+        // Enemy king attacks are also unsafe for the queen -- a free
+        // O(1) table lookup by king square, independent of eval order
+        // (unlike the enemy minor/rook attacks above, which do need
+        // both colors' knight/bishop/rook passes to finish first, and
+        // already have by queen's turn: see the eval call order in
+        // Eval() below). Only unsafe when the queen wouldn't be
+        // recaptured by something of our own first -- if a friendly
+        // pawn/minor/rook already covers that square, the king can't
+        // just take the queen for free. Every one of those tables (ours
+        // AND the enemy's) is fully populated by now: pawns, minors,
+        // and rooks all run their own eval pass before queen does.
+        //
+        BITBOARD bbUnsafeForQueen = pos->bbPawnAttacks[xColor] |
+                                     pos->bbMinorAttacks[xColor] |
+                                     pos->bbRookAttacks[xColor] |
+                                     (g_KingAttacksBB[cKing] &
+                                      ~(pos->bbPawnAttacks[uColor] |
+                                        pos->bbMinorAttacks[uColor] |
+                                        pos->bbRookAttacks[uColor]));
         BITBOARD bbAttackTotal = 0;
         BITBOARD bbXrayAccum = 0;
         BITBOARD bbMobility = 0;
@@ -4963,7 +5057,7 @@ Return value:
     // pieces are trapped!
     if (uTotalMobility == 0)
     {
-        _RecordTrappedCandidate(pos, uColor, c);
+        _RecordTrappedCandidate(pos, uColor, c, 0);
     }
 }
 
@@ -5494,6 +5588,7 @@ Return value:
 {
     BITBOARD bb[2];
     ULONG uColor;
+    ULONG xColor;
     int d1;
     COOR cQueen;
     COOR cKing, c;
@@ -5523,7 +5618,8 @@ Return value:
                               (pos->bbPawns[WHITE] != 0));
     FOREACH_COLOR(uColor)
     {
-        if (TotalNonPawnCount(pos, FLIP(uColor)) == 1)
+        xColor = FLIP(uColor);
+        if (TotalNonPawnCount(pos, xColor) == 1)
         {
             d1 = 16 * g_iAhead[uColor];
             ASSERT((d1 * 2) == (32 * g_iAhead[uColor]));
@@ -5534,10 +5630,10 @@ Return value:
                 {
                     // If the enemy king can take this passer and is
                     // on the move, all bets are off!
-                    cKing = KingPosition(pos, FLIP(uColor));
+                    cKing = KingPosition(pos, xColor);
                     ASSERT(IS_KING(pos->rgSquare[cKing].pPiece));
                     ASSERT(GET_COLOR(pos->rgSquare[cKing].pPiece) != uColor);
-                    if (pos->uToMove == FLIP(uColor) &&
+                    if (pos->uToMove == xColor &&
                         (DISTANCE(cKing, c) == 1))
                     {
                         // TODO: something clever here about protected pawns
@@ -5608,7 +5704,7 @@ Return value:
                     uKingDist = DISTANCE(cKing, cQueen);
                     if (uKingDist > 0)
                     {
-                        uKingDist -= (pos->uToMove == FLIP(uColor));
+                        uKingDist -= (pos->uToMove == xColor);
                     }
                     ASSERT((uKingDist >= 0) && (uPawnDist <= 7));
 
@@ -5701,6 +5797,7 @@ Return value:
 {
     ULONG u;
     ULONG uColor;
+    ULONG xColor;
     COOR c;
     COOR cSquare;
     BITBOARD bb;
@@ -5714,6 +5811,7 @@ Return value:
 
     FOREACH_COLOR(uColor)
     {
+        xColor = FLIP(uColor);
         bb = pHash->bbPasserLocations[uColor];
         if (bb != 0)
         {
@@ -5730,7 +5828,7 @@ Return value:
                 cSquare = c + d1;
                 ASSERT(IS_ON_BOARD(cSquare));
                 u = _WhoControlsSquareFast(pos, cSquare);
-                if (u == FLIP(uColor))
+                if (u == xColor)
                 {
                     EVAL_TERM(uColor,
                               PAWN,
@@ -5772,16 +5870,16 @@ Return value:
                     //
                     // The enemy king is ahead of the passer
                     //
-                    i += FILE_DISTANCE(c, KingPosition(pos, FLIP(uColor))) * 4;
+                    i += FILE_DISTANCE(c, KingPosition(pos, xColor)) * 4;
                 }
                 else
                 {
                     //
                     // The enemy king is behind the passer
                     //
-                    i += 10 + DISTANCE(c, KingPosition(pos, FLIP(uColor))) * 4;
+                    i += 10 + DISTANCE(c, KingPosition(pos, xColor)) * 4;
                 }
-                i *= PASSER_MATERIAL_UP_SCALER[pos->uArmyScaler[FLIP(uColor)]];
+                i *= PASSER_MATERIAL_UP_SCALER[pos->uArmyScaler[xColor]];
                 i /= 8;
                 EVAL_TERM(uColor,
                           PAWN,
@@ -5795,7 +5893,7 @@ Return value:
                 // are even more dangerous.
                 //
                 if (TotalNonPawnCount(pos, uColor) >
-                    TotalNonPawnCount(pos, FLIP(uColor)))
+                    TotalNonPawnCount(pos, xColor))
                 {
                     i = (PASSER_BY_RANK[uColor][RANK(c)] / 2);
                     EVAL_TERM(uColor,
@@ -5976,32 +6074,120 @@ Return value:
     COOR cBestOwnTrapped;
     ULONG uBestOwnTrappedValue;
     ULONG uColor;
+    ULONG xColor;
     ULONG u;
+    ULONG uFinalMobility;
+    BITBOARD bbOwnDefend;
+    BITBOARD bbUnsafeNow;
+    BITBOARD bbStillSafe;
     POSITION *pos = &ctx->sPosition;
     PIECE p;
+    SCORE i;
 
     FOREACH_COLOR(uColor)
     {
+        xColor = FLIP(uColor);
         cBestOwnTrapped = ILLEGAL_COOR;
         uBestOwnTrappedValue = 0;
         for (u = 0; u < pos->uNumTrapped[uColor]; u++)
         {
             c = pos->cTrapped[uColor][u];
             ASSERT(IS_ON_BOARD(c));
-            if (_WhoControlsSquareFast(pos, c) == FLIP(uColor))
-            {
-                // Unconditional even outside DEBUG builds: EVAL_TERM
-                // below reads p unconditionally (its PIE argument
-                // feeds EvalTrace() in EVAL_TRACE builds), so an
-                // assignment gated behind #ifdef DEBUG alone left p
-                // uninitialized on read in a non-DEBUG/EVAL_TRACE
-                // build.
-                p = pos->rgSquare[c].pPiece;
+            p = pos->rgSquare[c].pPiece;
 #ifdef DEBUG
-                ASSERT(p);
-                ASSERT(!IS_PAWN(p));
-                ASSERT(GET_COLOR(p) == uColor);
+            ASSERT(p);
+            ASSERT(!IS_PAWN(p));
+            ASSERT(GET_COLOR(p) == uColor);
 #endif
+
+            // A nonzero bbTrappedEscapes snapshot means this candidate
+            // was genuinely deferred (a bishop/knight/rook nominated at
+            // low-but-nonzero partial-information mobility -- see
+            // EVAL_MOBILITY_CAREFULLY_BELOW's comment) and is still
+            // owed both its real mobility score (skipped at nomination
+            // time) and a final trapped/not-trapped verdict, now that
+            // every piece type -- including the enemy king -- has
+            // contributed to the attack tables. A zero snapshot means
+            // either a genuinely 0-mobility piece (already scored
+            // inline, nothing left to re-derive -- see _EvalBishop's
+            // comment on why those are never deferred) or a queen
+            // (never deferred at all -- its own eval pass already runs
+            // after every smaller piece type, so it doesn't have this
+            // partial-information problem in the first place; see
+            // _EvalQueen's bbUnsafeForQueen).
+            if (pos->bbTrappedEscapes[uColor][u] != 0)
+            {
+                // bbOwnDefend excludes the candidate's own piece-type
+                // bucket: bbMinorAttacks/bbRookAttacks already include
+                // this very piece's own attack squares (populated
+                // unconditionally before the nomination decision),
+                // which are exactly its candidate escape squares --
+                // crediting that back as "defense" would be circular (a
+                // piece can't defend the square it would occupy after
+                // moving off its own square). Conservative side effect:
+                // a genuinely different friendly minor/rook defending
+                // the same square as a trapped minor/rook is also
+                // excluded, since the merged bitboards can't
+                // distinguish "this piece" from "another piece of the
+                // same bucket" -- known limitation, not fixed here.
+                bbOwnDefend = pos->bbPawnAttacks[uColor] |
+                              pos->bbQueenAttacks[uColor];
+                if (!IS_BISHOP(p) && !IS_KNIGHT(p))
+                {
+                    bbOwnDefend |= pos->bbMinorAttacks[uColor];
+                }
+                if (!IS_ROOK(p))
+                {
+                    bbOwnDefend |= pos->bbRookAttacks[uColor];
+                }
+
+                // The only thing nomination-time couldn't see: the
+                // enemy king's own attacks (pos->bbKingAttacks[xColor]
+                // -- both kings have finished evaluating well before
+                // _EvalTrappedPieces runs, see Eval()'s call order).
+                // Everything else a candidate square could be unsafe
+                // for (a cheaper enemy piece attacking it) was already
+                // known and excluded at nomination time -- see
+                // EVAL_MOBILITY_CAREFULLY_BELOW's comment.
+                bbUnsafeNow = pos->bbKingAttacks[xColor] & ~bbOwnDefend;
+                bbStillSafe = pos->bbTrappedEscapes[uColor][u] & ~bbUnsafeNow;
+                uFinalMobility = CountBits(bbStillSafe);
+
+                if (IS_BISHOP(p))
+                {
+                    EVAL_TERM(uColor, BISHOP, c, pos->iScore[uColor],
+                              BISHOP_MOBILITY_BY_SQUARES[uFinalMobility],
+                              "bishop mobility (deferred)");
+                }
+                else if (IS_KNIGHT(p))
+                {
+                    EVAL_TERM(uColor, KNIGHT, c, pos->iScore[uColor],
+                              KNIGHT_MOBILITY_BY_COUNT[uFinalMobility],
+                              "knight mobility (deferred)");
+                }
+                else if (IS_ROOK(p))
+                {
+                    ASSERT(pos->uArmyScaler[xColor] <= 31);
+                    i = ROOK_MOBILITY_BY_SQUARES[uFinalMobility];
+                    i *= (int)(REDUCED_MATERIAL_UP_SCALER[pos->uArmyScaler[xColor]] + 1);
+                    i /= 8;
+                    EVAL_TERM(uColor, ROOK, c, pos->iScore[uColor], i,
+                              "rook mobility (deferred)");
+                }
+
+                if (bbStillSafe != 0)
+                {
+                    // A real escape exists once full attack information
+                    // is in -- the loose, partial-information nomination
+                    // was a false alarm, not actually trapped. Its
+                    // (corrected, lower) mobility score was already
+                    // banked above; nothing more to do for it.
+                    continue;
+                }
+            }
+
+            if (_WhoControlsSquareFast(pos, c) == xColor)
+            {
                 // See if the side who created the trap and controls
                 // the square the trapped piece is sitting on has the
                 // move too.  If so, uColor moved at ply-1.