perf: qualify hidden aggregate columns for JOIN FetchRow cache

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

_FiveSql2/src/TSqlExecutor.prg

@@ -1297,7 +1297,11 @@ METHOD RunSelect() CLASS TSqlExecutor
          IF aCols[ i ][ 1 ][ 1 ] == ND_FN .AND. Len( aCols[ i ][ 1 ][ 3 ] ) > 0
             xArgExpr := aCols[ i ][ 1 ][ 3 ][ 1 ]
             IF xArgExpr[ 1 ] == ND_COL .AND. xArgExpr[ 2 ] != "*"
-               cBare := SqlExprName( xArgExpr )
+               /* Use the FULL qualified name (e.g. "o.amount") so
+                * FetchRow → FindWA resolves to the right workarea
+                * in JOIN contexts. Bare "amount" would fall through
+                * to aTables[1] which may be a different table. */
+               cBare := xArgExpr[ 2 ]
                lFound := .F.
                FOR j := 1 TO Len( aResultExprs )
                   IF Upper( aResultExprs[ j ][ 2 ] ) == Upper( cBare )