fix: 强化 CPU/memory checker 错误处理、timeout 遵守和快照校验

- Memory checker: reader 与 ctx.signal race，abort 返回 memory/timeout，reject 保持 memory/snapshot
- CPU checker: 第二次快照异常返回 cpu/snapshot，计算前校验空数组/核心数不一致/非有限值/负 delta
- CPU 计算: 零 delta 安全处理，observation 不含 NaN/Infinity
- 文档: CPU 互补描述修正，Memory timeout 约束说明
- 测试: +18 覆盖 timeout、异常和边界输入

tests/server/checker/runner/cpu/calculate.test.ts

@@ -2,7 +2,7 @@ import { describe, expect, test } from "bun:test";
 
 import type { CpuCoreSnapshot } from "../../../../../src/server/checker/runner/cpu/types";
 
-import { calculateCpuStats } from "../../../../../src/server/checker/runner/cpu/calculate";
+import { calculateCpuStats, validateCpuSnapshots } from "../../../../../src/server/checker/runner/cpu/calculate";
 
 function makeCore(user: number, nice: number, sys: number, idle: number, irq: number): CpuCoreSnapshot {
   return { times: { idle, irq, nice, sys, user } };
@@ -110,3 +110,68 @@ describe("calculateCpuStats", () => {
     expect(stats.usagePercent).toBe(60);
   });
 });
+
+describe("validateCpuSnapshots", () => {
+  test("合法 snapshot 返回 null", () => {
+    const before = [makeCore(100, 0, 0, 900, 0)];
+    const after = [makeCore(200, 0, 0, 800, 0)];
+    expect(validateCpuSnapshots(before, after)).toBeNull();
+  });
+
+  test("空 before snapshot", () => {
+    const after = [makeCore(0, 0, 0, 0, 0)];
+    expect(validateCpuSnapshots([], after)).toBe("CPU 快照为空");
+  });
+
+  test("空 after snapshot", () => {
+    const before = [makeCore(0, 0, 0, 0, 0)];
+    expect(validateCpuSnapshots(before, [])).toBe("CPU 快照为空");
+  });
+
+  test("核心数不一致", () => {
+    const before = [makeCore(0, 0, 0, 0, 0)];
+    const after = [makeCore(0, 0, 0, 0, 0), makeCore(0, 0, 0, 0, 0)];
+    expect(validateCpuSnapshots(before, after)).toBe("CPU 快照核心数不一致: before=1, after=2");
+  });
+
+  test("before 包含 NaN time 值", () => {
+    const before = [{ times: { idle: NaN, irq: 0, nice: 0, sys: 0, user: 0 } }];
+    const after = [makeCore(0, 0, 0, 0, 0)];
+    const error = validateCpuSnapshots(before, after);
+    expect(error).toContain("非有限值");
+    expect(error).toContain("before[0]");
+  });
+
+  test("after 包含 Infinity time 值", () => {
+    const before = [makeCore(0, 0, 0, 0, 0)];
+    const after = [{ times: { idle: Infinity, irq: 0, nice: 0, sys: 0, user: 0 } }];
+    const error = validateCpuSnapshots(before, after);
+    expect(error).toContain("非有限值");
+    expect(error).toContain("after[0]");
+  });
+
+  test("负数 total delta", () => {
+    const before = [makeCore(1000, 0, 0, 0, 0)];
+    const after = [makeCore(100, 0, 0, 0, 0)];
+    const error = validateCpuSnapshots(before, after);
+    expect(error).toContain("负数 delta");
+  });
+
+  test("零 delta 合法", () => {
+    const before = [makeCore(100, 0, 0, 100, 0)];
+    const after = [makeCore(100, 0, 0, 100, 0)];
+    expect(validateCpuSnapshots(before, after)).toBeNull();
+  });
+
+  test("零 delta 不产生除零错误", () => {
+    const before = [makeCore(100, 0, 0, 100, 0)];
+    const after = [makeCore(100, 0, 0, 100, 0)];
+    const stats = calculateCpuStats(before, after);
+    expect(Number.isFinite(stats.usagePercent)).toBe(true);
+    expect(Number.isFinite(stats.idlePercent)).toBe(true);
+    expect(Number.isFinite(stats.maxCoreUsagePercent)).toBe(true);
+    expect(Number.isFinite(stats.minCoreUsagePercent)).toBe(true);
+    expect(stats.usagePercent).toBe(0);
+    expect(stats.idlePercent).toBe(0);
+  });
+});