fix(client): count opponents correctly when the local seat is eliminated

client/src/hooks/__tests__/liveOpponents.test.ts

@@ -0,0 +1,49 @@
+import { describe, expect, it } from "vitest";
+
+import { countLiveOpponents } from "../liveOpponents";
+
+describe("countLiveOpponents", () => {
+  it("counts the live seats other than the local human", () => {
+    expect(
+      countLiveOpponents([
+        { id: 0, is_eliminated: false },
+        { id: 1, is_eliminated: false },
+        { id: 2, is_eliminated: false },
+      ]),
+    ).toBe(2);
+  });
+
+  it("does not subtract the local seat when seat 0 is eliminated", () => {
+    // Regression: the old `Math.max(0, liveCount - 1)` undercounted this to 1.
+    expect(
+      countLiveOpponents([
+        { id: 0, is_eliminated: true },
+        { id: 1, is_eliminated: false },
+        { id: 2, is_eliminated: false },
+      ]),
+    ).toBe(2);
+  });
+
+  it("excludes eliminated opponents", () => {
+    expect(
+      countLiveOpponents([
+        { id: 0, is_eliminated: false },
+        { id: 1, is_eliminated: true },
+        { id: 2, is_eliminated: false },
+      ]),
+    ).toBe(1);
+  });
+
+  it("is zero when only the local human remains", () => {
+    expect(countLiveOpponents([{ id: 0, is_eliminated: false }])).toBe(0);
+  });
+
+  it("is zero when everyone is eliminated", () => {
+    expect(
+      countLiveOpponents([
+        { id: 0, is_eliminated: true },
+        { id: 1, is_eliminated: true },
+      ]),
+    ).toBe(0);
+  });
+});

client/src/hooks/liveOpponents.ts

@@ -0,0 +1,22 @@
+/** A player as the resumable-match summary sees it (a structural subset of the
+ *  engine `Player`, whose `is_eliminated` is optional on the wire — an absent
+ *  flag means "not eliminated"). */
+export interface ResumableSummaryPlayer {
+  id: number;
+  is_eliminated?: boolean;
+}
+
+/**
+ * Number of live opponents for the local human (seat 0) in a resumable match.
+ *
+ * Per CR 800.4 an eliminated player is out, so opponents are the live seats
+ * other than you. Only subtract the local seat when it is itself still alive:
+ * if seat 0 has been eliminated but the match is still resumable (a multi-seat
+ * local / FFA game), it is not among the live seats, so every live seat is an
+ * opponent and there is nothing to subtract.
+ */
+export function countLiveOpponents(players: ResumableSummaryPlayer[]): number {
+  const you = players.find((p) => p.id === 0);
+  const liveCount = players.filter((p) => !p.is_eliminated).length;
+  return liveCount - (you && !you.is_eliminated ? 1 : 0);
+}

client/src/hooks/useResumables.ts

@@ -1,6 +1,7 @@
 import { useEffect, useState } from "react";
 import { useNavigate } from "react-router";
 
+import { countLiveOpponents } from "./liveOpponents";
 import { loadP2PSession } from "../services/p2pSession";
 import { loadWsSession } from "../services/multiplayerSession";
 import {
@@ -86,12 +87,11 @@ export function useResumables(): Resumables {
           // CR 800.4: eliminated players are out — only live seats count as
           // opponents. Seat 0 is the local human in AI/host matches.
           const you = state.players.find((p) => p.id === 0);
-          const liveCount = state.players.filter((p) => !p.is_eliminated).length;
           setMatchSummary({
             turn: state.turn_number,
             isYourTurn: state.active_player === 0,
             yourLife: you && !you.is_eliminated ? you.life : null,
-            opponentCount: Math.max(0, liveCount - 1),
+            opponentCount: countLiveOpponents(state.players),
           });
         } else {
           clearActiveGame();