feat(server): per-viewer capture tally on joined and update messages

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/server/src/captures.ts

@@ -0,0 +1,20 @@
+import type { CaptureTally, Color } from '@blind-chess/shared';
+import type { Game } from './state.js';
+
+/**
+ * Per-viewer capture tally derived from move history. `byYou` is the set of
+ * opponent pieces this viewer has captured; `byOpponent` is the set of this
+ * viewer's pieces the opponent has captured. Pure function of move history —
+ * no live board state, no opponent positions.
+ */
+export function captureTally(game: Game, viewer: Color): CaptureTally {
+  const byYou: Record<string, number> = {};
+  const byOpponent: Record<string, number> = {};
+  for (const rec of game.moveHistory) {
+    const captured = rec.capturedPieceType;
+    if (!captured) continue;
+    const bucket = rec.by === viewer ? byYou : byOpponent;
+    bucket[captured] = (bucket[captured] ?? 0) + 1;
+  }
+  return { byYou, byOpponent };
+}

packages/server/src/ws.ts

@@ -19,6 +19,7 @@ import { announce } from './translator.js';
 import { buildView } from './view.js';
 import { consumeCommitToken } from './ratelimit.js';
 import { endGame, finalizeIfEnded } from './game-end.js';
+import { captureTally } from './captures.js';
 
 async function pokeBot(game: Game): Promise<void> {
   const driver = getBotDriver(game.id);
@@ -147,6 +148,7 @@ async function onHello(ctx: SocketCtx, msg: Extract<ClientMessage, { type: 'hell
     mode: game.mode,
     highlightingEnabled: game.highlightingEnabled,
     opponentConnected: !!game.players[color === 'w' ? 'b' : 'w']?.socket,
+    captures: captureTally(game, color),
     aiOpponent: game.aiOpponent,
   });
 
@@ -284,6 +286,7 @@ function sendUpdateTo(
     drawOffer,
     endReason: game.endReason,
     winner: game.winner ?? null,
+    captures: captureTally(game, color),
     aiOpponent: game.aiOpponent,
   });
 }

packages/server/test/unit/captures.test.ts

@@ -0,0 +1,32 @@
+import { describe, it, expect } from 'vitest';
+import { captureTally } from '../../src/captures.js';
+import type { Game, MoveRecord } from '../../src/state.js';
+import type { Color, PieceType } from '@blind-chess/shared';
+
+function rec(by: Color, capturedPieceType?: PieceType): MoveRecord {
+  return {
+    ply: 1, by, from: 'e2', to: 'e4', san: 'e4',
+    capturedPieceType, flags: {}, at: 0,
+  };
+}
+
+describe('captureTally', () => {
+  it('counts captures per viewer', () => {
+    const moveHistory: MoveRecord[] = [
+      rec('w', 'p'), rec('b'), rec('w', 'n'),
+      rec('b', 'p'), rec('w', 'p'),
+    ];
+    const game = { moveHistory } as unknown as Game;
+    expect(captureTally(game, 'w')).toEqual({
+      byYou: { p: 2, n: 1 }, byOpponent: { p: 1 },
+    });
+    expect(captureTally(game, 'b')).toEqual({
+      byYou: { p: 1 }, byOpponent: { p: 2, n: 1 },
+    });
+  });
+
+  it('returns empty tallies when there are no captures', () => {
+    const game = { moveHistory: [rec('w'), rec('b')] } as unknown as Game;
+    expect(captureTally(game, 'w')).toEqual({ byYou: {}, byOpponent: {} });
+  });
+});

packages/shared/src/protocol.ts

@@ -1,5 +1,5 @@
 import type {
-  BoardView, Color, GameId, GameStatus, Mode, PlayerToken,
+  BoardView, CaptureTally, Color, GameId, GameStatus, Mode, PlayerToken,
   PromotionType, Square, EndReason,
 } from './types.js';
 import type { Announcement } from './moderator.js';
@@ -34,6 +34,7 @@ export type ServerMessage =
       mode: Mode;
       highlightingEnabled: boolean;
       opponentConnected: boolean;
+      captures: CaptureTally;
       aiOpponent?: { color: Color; brain: 'casual' | 'recon' };
     }
   | {
@@ -45,6 +46,7 @@ export type ServerMessage =
       drawOffer?: { from: Color } | null;
       endReason?: EndReason;
       winner?: Color | null;
+      captures: CaptureTally;
       aiOpponent?: { color: Color; brain: 'casual' | 'recon' };
     }
   | { type: 'peer-status'; color: Color; connected: boolean; graceUntil?: number }

packages/shared/src/types.ts

@@ -61,3 +61,12 @@ export function squareAt(fileIdx: number, rankIdx: number): Square | null {
   const r = String.fromCharCode('1'.charCodeAt(0) + rankIdx);
   return `${f}${r}` as Square;
 }
+
+/** Count of pieces by type — used for the capture tally. */
+export type PieceTally = Partial<Record<PieceType, number>>;
+
+/** Per-viewer capture tally: what you took, and what you lost. */
+export interface CaptureTally {
+  byYou: PieceTally;
+  byOpponent: PieceTally;
+}