feat(deepsearch): 联网检索插件 + SearXNG 生命周期托管

把原 websearch 示例改名为 deepsearch（目录/go.mod/plg.json/工具前缀/README 全量对齐，
工具名 websearch_* → deepsearch_*）。

新增 searxng.go：插件自己托管搜索后端
- 启动探 healthz：已在跑则直接接管（不重启），没跑就 docker compose up -d 并等就绪
- 关闭动作注册为 stop handler（幂等、限时 4s < 内核 5s 宽限期）
- 配置 manage_searxng / searxng_dir / stop_searxng_on_exit
- 崩溃/被 kill 时不关后端（下次启动接管）：安全失败方向
- 可注入 cmdRunner + 时间预算，8 项单测离线覆盖接管/拉起/失败/幂等/保留

契约依据（internal/plugin/proc）：停止插件 = plugin.stop → RunStopHandlers（LIFO、
幂等）→ Stop() → exit(0)，宽限期 5s；stdin 关闭同路径。

验证：19 项单测（18 通过 + 1 联调跳过）、-race 干净、vet/gofmt 干净；内核 E2E 真调用
返回 58 条/37 条、58/58 带摘要；线上 daemon 实测 stop handler 与冷启动（约 3s）。

example/deepsearch/searxng_test.go

@@ -0,0 +1,197 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+type fakeCall struct {
+	dir  string
+	name string
+	args []string
+}
+
+func (c fakeCall) String() string { return c.name + " " + strings.Join(c.args, " ") }
+
+// newFakeRunner 记录调用并返回预设结果
+func newFakeRunner(calls *[]fakeCall, out string, err error) cmdRunner {
+	var mu sync.Mutex
+	return func(ctx context.Context, dir, name string, args ...string) (string, error) {
+		mu.Lock()
+		*calls = append(*calls, fakeCall{dir: dir, name: name, args: args})
+		mu.Unlock()
+		return out, err
+	}
+}
+
+// fastBudget 把就绪窗口压到毫秒级，避免单测真等
+func fastBudget() searxBudget {
+	return searxBudget{
+		probe:    50 * time.Millisecond,
+		up:       time.Second,
+		ready:    200 * time.Millisecond,
+		shutdown: time.Second,
+	}
+}
+
+// 1) 后端没跑 → 应执行 docker compose up -d，并认领关闭责任
+func TestEnsureSearxngStartsWhenUnreachable(t *testing.T) {
+	var calls []fakeCall
+	p := &Plugin{
+		name: "deepsearch", searxURL: "http://127.0.0.1:1", searxDir: "/tmp/fake-searx",
+		manageSearx: true, stopOnExit: true, userAgent: "test",
+		bud: fastBudget(), run: newFakeRunner(&calls, "Container searxng-agent Started", nil),
+	}
+	p.ensureSearxng()
+
+	if len(calls) != 1 {
+		t.Fatalf("应恰好拉起一次，实际 %d 次：%v", len(calls), calls)
+	}
+	got := calls[0]
+	if got.name != "docker" || strings.Join(got.args, " ") != "compose up -d" {
+		t.Errorf("命令不对：%s", got)
+	}
+	if got.dir != "/tmp/fake-searx" {
+		t.Errorf("工作目录应为配置的 compose 目录，实际 %q", got.dir)
+	}
+	if !p.searxOwned {
+		t.Error("既然是我们拉起的，就应认领关闭责任")
+	}
+}
+
+// 2) 后端已在跑 → 不重启，直接接管
+func TestEnsureSearxngAdoptsRunningBackend(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/healthz" {
+			_, _ = w.Write([]byte("OK"))
+			return
+		}
+		http.NotFound(w, r)
+	}))
+	defer srv.Close()
+
+	var calls []fakeCall
+	p := &Plugin{
+		name: "deepsearch", searxURL: srv.URL, searxDir: "/tmp/fake-searx",
+		manageSearx: true, stopOnExit: true, userAgent: "test",
+		bud: fastBudget(), run: newFakeRunner(&calls, "", nil),
+	}
+	p.ensureSearxng()
+
+	if len(calls) != 0 {
+		t.Errorf("已在跑就不该重启它，实际执行了：%v", calls)
+	}
+	if !p.searxOwned {
+		t.Error("接管后也应负责停止（与「不重启」不冲突）")
+	}
+}
+
+// 3) 关掉托管 → 完全不碰 docker
+func TestEnsureSearxngDisabled(t *testing.T) {
+	var calls []fakeCall
+	p := &Plugin{
+		name: "deepsearch", searxURL: "http://127.0.0.1:1", searxDir: "/tmp/fake-searx",
+		manageSearx: false, stopOnExit: true, userAgent: "test",
+		bud: fastBudget(), run: newFakeRunner(&calls, "", nil),
+	}
+	p.ensureSearxng()
+	if len(calls) != 0 || p.searxOwned {
+		t.Errorf("manage_searxng=false 时不该有任何动作：calls=%v owned=%v", calls, p.searxOwned)
+	}
+}
+
+// 4) 拉起失败不能让插件起不来（记日志即可）
+func TestEnsureSearxngFailureNonFatal(t *testing.T) {
+	var calls []fakeCall
+	p := &Plugin{
+		name: "deepsearch", searxURL: "http://127.0.0.1:1", searxDir: "/tmp/fake-searx",
+		manageSearx: true, stopOnExit: true, userAgent: "test",
+		bud: fastBudget(), run: newFakeRunner(&calls, "Cannot connect to the Docker daemon", errors.New("exit status 1")),
+	}
+	p.ensureSearxng() // 不应 panic
+	if p.searxOwned {
+		t.Error("没拉起来就不该认领关闭责任（否则停止时会去关一个不是我们起的服务）")
+	}
+}
+
+// 5) 停止：关掉我们拉起的后端，且幂等
+func TestShutdownStopsOwnedBackend(t *testing.T) {
+	var calls []fakeCall
+	runner := newFakeRunner(&calls, "ok", nil)
+	p := &Plugin{
+		name: "deepsearch", searxURL: "http://127.0.0.1:1", searxDir: "/tmp/fake-searx",
+		manageSearx: true, stopOnExit: true, userAgent: "test",
+		bud: fastBudget(), run: runner,
+	}
+	p.ensureSearxng()
+	calls = nil
+
+	p.shutdownSearxng()
+	if len(calls) != 1 {
+		t.Fatalf("应执行一次 compose stop，实际 %v", calls)
+	}
+	if got := strings.Join(calls[0].args, " "); !strings.HasPrefix(got, "compose stop") {
+		t.Errorf("停止命令不对：%s", got)
+	}
+	if p.searxOwned {
+		t.Error("停止后应清掉认领标记")
+	}
+
+	p.shutdownSearxng() // 幂等：不应再调一次
+	if len(calls) != 1 {
+		t.Errorf("重复停止应无副作用，实际 %v", calls)
+	}
+}
+
+// 6) 不是我们拉起的 → 停止时不许动它
+func TestShutdownSkippedWhenNotOwned(t *testing.T) {
+	var calls []fakeCall
+	p := &Plugin{
+		name: "deepsearch", searxDir: "/tmp/fake-searx", manageSearx: true, stopOnExit: true,
+		bud: fastBudget(), run: newFakeRunner(&calls, "", nil),
+	}
+	p.shutdownSearxng()
+	if len(calls) != 0 {
+		t.Errorf("不该去停一个我们没起的服务：%v", calls)
+	}
+}
+
+// 7) 配了「停止时保留」→ 认领过也不关
+func TestShutdownKeepsBackendWhenConfigured(t *testing.T) {
+	var calls []fakeCall
+	p := &Plugin{
+		name: "deepsearch", searxURL: "http://127.0.0.1:1", searxDir: "/tmp/fake-searx",
+		manageSearx: true, stopOnExit: false, userAgent: "test",
+		bud: fastBudget(), run: newFakeRunner(&calls, "", nil),
+	}
+	p.ensureSearxng()
+	calls = nil
+	p.shutdownSearxng()
+	if len(calls) != 0 {
+		t.Errorf("stop_searxng_on_exit=false 时不应关闭：%v", calls)
+	}
+}
+
+// 8) Stop() 自身也要收尾（内核 stdin 关闭路径不会走 stop handler 的注册顺序之外）
+func TestStopTriggersShutdown(t *testing.T) {
+	var calls []fakeCall
+	p := &Plugin{
+		name: "deepsearch", searxURL: "http://127.0.0.1:1", searxDir: "/tmp/fake-searx",
+		manageSearx: true, stopOnExit: true, userAgent: "test",
+		bud: fastBudget(), run: newFakeRunner(&calls, "", nil),
+	}
+	p.ensureSearxng()
+	calls = nil
+	if err := p.Stop(); err != nil {
+		t.Fatalf("Stop 返回错误: %v", err)
+	}
+	if len(calls) != 1 {
+		t.Errorf("Stop 应触发一次关闭，实际 %v", calls)
+	}
+}