💥 feat(agent)!: 添加主机监控代理首版

* 实现周期采集、快照缓存、本地 HTTP API 和主动上报

* 补齐 Linux 和 Windows 主机、网络、资源、进程和 TCP 采集

* 添加服务生命周期管理、配置加载、构建脚本和测试覆盖

BREAKING CHANGE: network.ips 拆分为 network.ipv4s 和 network.ipv6s。

internal/snapshot/snapshot_test.go

@@ -0,0 +1,103 @@
+package snapshot
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"mfd-monitor-agent/internal/status"
+)
+
+// TestCollectorFailuresReturnPartialSnapshot verifies failed collectors do not fail snapshots.
+func TestCollectorFailuresReturnPartialSnapshot(t *testing.T) {
+	cache := NewCache([]Collector{
+		CollectorFunc(func(context.Context, *status.HostStatus) error {
+			return nil
+		}),
+		CollectorFunc(func(context.Context, *status.HostStatus) error {
+			return errors.New("permission denied")
+		}),
+	}, "test", time.Now())
+
+	got := cache.Collect(context.Background())
+
+	if got.Agent.SnapshotStatus != "partial" {
+		t.Fatalf("snapshot status = %q", got.Agent.SnapshotStatus)
+	}
+	if len(got.Errors) != 1 || got.Errors[0].Message != "permission denied" {
+		t.Fatalf("errors = %+v", got.Errors)
+	}
+}
+
+// TestCacheStoresLastSnapshot verifies successful collection is cached.
+func TestCacheStoresLastSnapshot(t *testing.T) {
+	cache := NewCache([]Collector{
+		CollectorFunc(func(_ context.Context, out *status.HostStatus) error {
+			out.Host.Hostname = "host-a"
+			return nil
+		}),
+	}, "test", time.Now())
+
+	cache.Collect(context.Background())
+	got, ok := cache.Get()
+
+	if !ok {
+		t.Fatal("expected cached snapshot")
+	}
+	if got.Host.Hostname != "host-a" {
+		t.Fatalf("hostname = %q", got.Host.Hostname)
+	}
+}
+
+// TestRunCollectsImmediately verifies Run collects before the first interval tick.
+func TestRunCollectsImmediately(t *testing.T) {
+	collected := make(chan struct{})
+	cache := NewCache([]Collector{
+		CollectorFunc(func(_ context.Context, out *status.HostStatus) error {
+			out.Host.Hostname = "host-a"
+			close(collected)
+			return nil
+		}),
+	}, "test", time.Now())
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go cache.Run(ctx, time.Hour, time.Second)
+
+	select {
+	case <-collected:
+	case <-time.After(time.Second):
+		t.Fatal("initial collection did not run")
+	}
+	got, ok := cache.Get()
+	if !ok {
+		t.Fatal("expected cached snapshot")
+	}
+	if got.Host.Hostname != "host-a" {
+		t.Fatalf("hostname = %q", got.Host.Hostname)
+	}
+}
+
+// TestCollectWithTimeoutMarksCanceledCollectorPartial verifies timeout errors are partial.
+func TestCollectWithTimeoutMarksCanceledCollectorPartial(t *testing.T) {
+	cache := NewCache([]Collector{
+		CollectorFunc(func(ctx context.Context, _ *status.HostStatus) error {
+			<-ctx.Done()
+			return ctx.Err()
+		}),
+	}, "test", time.Now())
+
+	cache.collectWithTimeout(context.Background(), time.Millisecond)
+	got, ok := cache.Get()
+
+	if !ok {
+		t.Fatal("expected cached snapshot")
+	}
+	if got.Agent.SnapshotStatus != "partial" {
+		t.Fatalf("snapshot status = %q", got.Agent.SnapshotStatus)
+	}
+	if len(got.Errors) != 1 || got.Errors[0].Message != context.DeadlineExceeded.Error() {
+		t.Fatalf("errors = %+v", got.Errors)
+	}
+}