Add seescores diagnostic command, verify zero SEE-value drift

Board-representation migration section 4 item 4: seescores <filename>
(command.c, registered alongside script/sd) reads setboard lines from
an EPD file (same convention tests/ecm*.ep_ already use), generates
legal moves per position, and prints (FEN, SAN move, SEE value) for
every capture -- meant to be run once per GetAttacksBB toggle state
and diffed, closing a gap TestGetAttacks's attacker-list comparison
can't: whether _GetAttacksBB's attacker lists, though set-identical to
asm GetAttacks, still produce identical SEE() output once fed through
_MinLegalPiece's exchange simulation.

Run against all three curated suites (747 captures total: 51 + 351 +
345), same-commit asm-vs-GETATTACKS_BITBOARD=1 A/B build (same pair
used for the earlier sd10 comparison) -- output byte-identical, zero
diff, on all three. Confirms _GetAttacksBB is correct all the way
through to the final SEE() score every move-ordering decision actually
uses, not just at the raw attacker-list level.

precommit_check.sh clean. Default (no flag) release binary restored
after testing.

Only match_play.py remains unmet before full retirement of the old
mailbox GetAttacks implementation (section 7) -- deliberately deferred,
not run this pass.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Jntky4yGUTyQVaGCXms4F2

2 files changed, 150 insertions, 8 deletions

diff --git a/src/board_representation/MIGRATION.md b/src/board_representation/MIGRATION.md
index 313c74d..c6673ce 100644
--- a/src/board_representation/MIGRATION.md
+++ b/src/board_representation/MIGRATION.md
@@ -15,12 +15,13 @@ inline as a note rather than deleted, so a future session designing
 the separate migration doesn't have to rediscover it from git history.
 
 **Status: sections 1-3 (`bbPieces`/`bbPawns`-backed
-`_WhoAttacksSquareBB`/`_GetAttacksBB`), section 4 items 1-3 and 5, and
-section 6 (the `GETATTACKS_BITBOARD` toggle) all implemented, verified,
-and committed -- including a whole-engine `sd10` check across all three
-curated suites showing zero solve-count regression and +8.38%
-aggregate NPS. Only `match_play.py` (section 4 item 6 / section 7)
-remains unmet before full retirement of the old mailbox
+`_WhoAttacksSquareBB`/`_GetAttacksBB`), all of section 4, and section 6
+(the `GETATTACKS_BITBOARD` toggle) implemented, verified, and
+committed -- including a whole-engine `sd10` check across all three
+curated suites (zero solve-count regression, +8.38% aggregate NPS) and
+a `seescores` SEE-value diff across all 747 captures in those suites
+(byte-identical, zero diff). Only `match_play.py` (section 4 item 6 /
+section 7) remains unmet before full retirement of the old mailbox
 implementation, deliberately deferred for now. Section 5's whole-engine
 item and section 7's remaining items are otherwise done; section 8 not
 started.** See the per-section status notes below for specifics.
@@ -461,7 +462,18 @@ sequence.
    ECM/random positions, run once per `GetAttacksBB` toggle state,
    diffed. Catches any behavioral drift `TestGetAttacks`'s raw-list
    comparison might miss once results feed into `_MinLegalPiece`'s
-   exchange simulation. Not started.
+   exchange simulation. **DONE.** `seescores <filename>` (`command.c`,
+   registered alongside `script`/`sd`) reads `setboard` lines from an
+   EPD file (the same convention `tests/ecm*.ep_` already use),
+   generates legal moves per position, and prints `(FEN, SAN move, SEE
+   value)` for every capture. Run against all three curated suites (747
+   captures total: 51 + 351 + 345), once per binary from section 4 item
+   5's same-commit asm-vs-`GETATTACKS_BITBOARD=1` A/B build -- output
+   **byte-identical, zero diff**, on all three. Confirms `_GetAttacksBB`
+   is correct not just at the attacker-list level (`TestGetAttacks`)
+   but all the way through `SEE()`/`_MinLegalPiece`'s exchange
+   simulation to the final score every move-ordering decision actually
+   uses.
 5. **Full-suite behavioral check is mandatory here, not optional** --
    this is the one place this migration is *riskier* than the Eval
    constant work: `GetAttacks` feeds move ordering and pruning decisions
diff --git a/src/command.c b/src/command.c
index a3361af..37686ed 100755
--- a/src/command.c
+++ b/src/command.c
@@ -1844,6 +1844,130 @@ COMMAND(SEECommand)
 }
 
 
+COMMAND(SeeScoresCommand)
+/**
+
+Routine description:
+
+    board_representation/MIGRATION.md section 4 item 4: for every
+    position in <filename> (lines starting with "setboard ", the same
+    EPD convention the 'script' command's suite files use -- see
+    tests/ecm*.ep_), compute SEE() for every legal capture and print
+    (FEN, SAN move, SEE value) triples in generation order. Meant to
+    be run once per GetAttacksBB toggle state and diffed -- catches
+    any behavioral drift TestGetAttacks's attacker-*list* comparison
+    can't see, since that test only checks GetAttacks's raw output,
+    not what SEE()/_MinLegalPiece's exchange simulation does with it
+    downstream.
+
+    Usage:
+
+        seescores <required filename>
+
+Parameters:
+
+    The COMMAND macro hides four arguments from the input parser:
+
+        CHAR *szInput : the full line of input
+        ULONG argc    : number of argument chunks
+        CHAR *argv[]  : array of ptrs to each argument chunk
+        POSITION *pos : a POSITION pointer to operate on (unused --
+            this command sets its own position per line of the file)
+
+Return value:
+
+    void
+
+**/
+{
+    FILE *pFile;
+    static CHAR szLine[SMALL_STRING_LEN_CHAR];
+    SEARCHER_THREAD_CONTEXT *ctx;
+    CHAR *szFen;
+    CHAR *p;
+    MOVE mv;
+    ULONG u;
+    ULONG uPositions = 0;
+    ULONG uCaptures = 0;
+
+    if (argc < 2)
+    {
+        Trace("Usage: seescores <required-filename>\n");
+        return;
+    }
+    if (FALSE == SystemDoesFileExist(argv[1]))
+    {
+        Trace("Error (file doesn't exist): %s\n", argv[1]);
+        return;
+    }
+    pFile = fopen(argv[1], "rb");
+    if (NULL == pFile)
+    {
+        Trace("Error (can't open file): %s\n", argv[1]);
+        return;
+    }
+    ctx = SystemAllocateMemory(sizeof(SEARCHER_THREAD_CONTEXT));
+    if (NULL == ctx)
+    {
+        fclose(pFile);
+        return;
+    }
+
+    while (fgets(szLine, ARRAY_LENGTH(szLine), pFile))
+    {
+        if (STRNCMPI(szLine, "setboard", 8))
+        {
+            continue;
+        }
+        szFen = szLine + 8;
+        while (' ' == *szFen)
+        {
+            szFen++;
+        }
+        p = strchr(szFen, '\r');
+        if (NULL != p) *p = '\0';
+        p = strchr(szFen, '\n');
+        if (NULL != p) *p = '\0';
+
+        if (FALSE == FenToPosition(&(ctx->sPosition), szFen))
+        {
+            Trace("SEESCORES: skipping malformed FEN: %s\n", szFen);
+            continue;
+        }
+        uPositions++;
+
+        mv.uMove = 0;
+        GenerateMoves(ctx, mv,
+                      (InCheck(&(ctx->sPosition), ctx->sPosition.uToMove) ?
+                       GENERATE_ESCAPES : GENERATE_ALL_MOVES));
+        ASSERT(ctx->uPly == 0);
+        for (u = ctx->sMoveStack.uBegin[0];
+             u < ctx->sMoveStack.uEnd[0];
+             u++)
+        {
+            mv = ctx->sMoveStack.mvf[u].mv;
+            if (!mv.pCaptured)
+            {
+                continue;
+            }
+            if (MakeMove(ctx, mv))
+            {
+                UnmakeMove(ctx, mv);
+                Trace("SEESCORES %s | %s | %d\n",
+                      szFen,
+                      MoveToSan(mv, &(ctx->sPosition)),
+                      SEE(&(ctx->sPosition), mv));
+                uCaptures++;
+            }
+        }
+    }
+    fclose(pFile);
+    SystemFreeMemory(ctx);
+    Trace("SEESCORES: %u position(s), %u capture(s) scored.\n",
+          uPositions, uCaptures);
+}
+
+
 COMMAND(TestCommand)
 /**
 
@@ -2404,11 +2528,17 @@ COMMAND_PARSER_ENTRY g_ParserTable[] =
       FALSE,
       "Run a script" },
     { "sd",
-      SearchDepthCommand, 
+      SearchDepthCommand,
       TRUE,
       FALSE,
       TRUE,
       "Set engine maximum search depth" },
+    { "seescores",
+      SeeScoresCommand,
+      FALSE,
+      FALSE,
+      FALSE,
+      "Dump SEE() for every legal capture in a batch of EPD positions" },
     { "set",
       SetCommand,
       TRUE,