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/execute.test.ts

@@ -210,6 +210,130 @@ describe("CpuChecker execute", () => {
     expect(result.failure?.path).toBe("timeout");
   });
 
+  test("第二次 snapshot 抛错返回 cpu/snapshot failure", async () => {
+    const before = [makeCore(0, 0, 0, 10000, 0)];
+    let callCount = 0;
+    const reader: SnapshotReader = () => {
+      callCount++;
+      if (callCount === 1) return before;
+      throw new Error("second snapshot failed");
+    };
+    const checker = new CpuChecker(reader);
+
+    const target: RawTargetConfig = { cpu: {}, id: "cpu-test", type: "cpu" };
+    const resolved = checker.resolve(target, makeResolveContext({ defaultTimeoutMs: 5000 }));
+
+    const ctx = { signal: new AbortController().signal };
+    const result = await checker.execute(resolved, ctx);
+
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("cpu");
+    expect(result.failure?.path).toBe("snapshot");
+    expect(result.observation).toBeNull();
+  });
+
+  test("空 snapshot pair 返回 cpu/snapshot failure", async () => {
+    const reader: SnapshotReader = () => [];
+    const checker = new CpuChecker(reader);
+
+    const target: RawTargetConfig = { cpu: {}, id: "cpu-test", type: "cpu" };
+    const resolved = checker.resolve(target, makeResolveContext({ defaultTimeoutMs: 5000 }));
+
+    const ctx = { signal: new AbortController().signal };
+    const result = await checker.execute(resolved, ctx);
+
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("cpu");
+    expect(result.failure?.path).toBe("snapshot");
+  });
+
+  test("核心数不一致返回 cpu/snapshot failure", async () => {
+    let callCount = 0;
+    const snapshots = [[makeCore(0, 0, 0, 100, 0)], [makeCore(0, 0, 0, 100, 0), makeCore(0, 0, 0, 100, 0)]];
+    const reader: SnapshotReader = () => {
+      const result = snapshots[Math.min(callCount, snapshots.length - 1)]!;
+      callCount++;
+      return result;
+    };
+    const checker = new CpuChecker(reader);
+
+    const target: RawTargetConfig = { cpu: {}, id: "cpu-test", type: "cpu" };
+    const resolved = checker.resolve(target, makeResolveContext({ defaultTimeoutMs: 5000 }));
+
+    const ctx = { signal: new AbortController().signal };
+    const result = await checker.execute(resolved, ctx);
+
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("cpu");
+    expect(result.failure?.path).toBe("snapshot");
+    expect(result.failure?.message).toContain("核心数不一致");
+  });
+
+  test("非有限 CPU time 值返回 cpu/snapshot failure", async () => {
+    let callCount = 0;
+    const snapshots: CpuCoreSnapshot[][] = [
+      [makeCore(0, 0, 0, 100, 0)],
+      [{ times: { idle: NaN, irq: 0, nice: 0, sys: 0, user: 100 } }],
+    ];
+    const reader: SnapshotReader = () => {
+      const result = snapshots[Math.min(callCount, snapshots.length - 1)]!;
+      callCount++;
+      return result;
+    };
+    const checker = new CpuChecker(reader);
+
+    const target: RawTargetConfig = { cpu: {}, id: "cpu-test", type: "cpu" };
+    const resolved = checker.resolve(target, makeResolveContext({ defaultTimeoutMs: 5000 }));
+
+    const ctx = { signal: new AbortController().signal };
+    const result = await checker.execute(resolved, ctx);
+
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("cpu");
+    expect(result.failure?.path).toBe("snapshot");
+    expect(result.failure?.message).toContain("非有限值");
+  });
+
+  test("负数 CPU time delta 返回 cpu/snapshot failure", async () => {
+    const before = [makeCore(1000, 0, 0, 0, 0)];
+    const after = [makeCore(100, 0, 0, 0, 0)];
+    const reader = makeSnapshotReader(before, after);
+    const checker = new CpuChecker(reader);
+
+    const target: RawTargetConfig = { cpu: {}, id: "cpu-test", type: "cpu" };
+    const resolved = checker.resolve(target, makeResolveContext({ defaultTimeoutMs: 5000 }));
+
+    const ctx = { signal: new AbortController().signal };
+    const result = await checker.execute(resolved, ctx);
+
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("cpu");
+    expect(result.failure?.path).toBe("snapshot");
+    expect(result.failure?.message).toContain("负数 delta");
+  });
+
+  test("零 delta snapshot 返回稳定安全值", async () => {
+    const before = [makeCore(100, 0, 0, 100, 0)];
+    const after = [makeCore(100, 0, 0, 100, 0)];
+    const reader = makeSnapshotReader(before, after);
+    const checker = new CpuChecker(reader);
+
+    const target: RawTargetConfig = { cpu: {}, id: "cpu-test", type: "cpu" };
+    const resolved = checker.resolve(target, makeResolveContext({ defaultTimeoutMs: 5000 }));
+
+    const ctx = { signal: new AbortController().signal };
+    const result = await checker.execute(resolved, ctx);
+
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+    expect(result.observation).toMatchObject({
+      idlePercent: 0,
+      maxCoreUsagePercent: 0,
+      minCoreUsagePercent: 0,
+      usagePercent: 0,
+    });
+  });
+
   test("includePerCore=true 时输出 perCoreUsagePercent", async () => {
     const before = [makeCore(0, 0, 0, 0, 0), makeCore(0, 0, 0, 0, 0)];
     const after = [makeCore(8000, 0, 0, 2000, 0), makeCore(2000, 0, 0, 8000, 0)];