feat(cluster): 停用改为「标记」语义，让 disabled 真正随令牌环跨节点传播

承接用户提问「设计上停用不是本来就会跨节点传输吗」——核实结论：结构上确实
如此（TopoEntry.Link 是完整 store.Link，整个 State 随 token 每轮广播），但
实际路径断了。断点正是「撤销会删掉 topology 条目」：条目是 flag 的载体，
删了就无处传播，于是停用只能靠一次性 revoke 任务投递给 owner，**owner 当时
不在线就收不到**（实测 .60 记 disabled=1 / .106 记 0，就是这么来的）。

## 改为标记而非移除

撤销不再 RemoveTopology，而是 UpdateTopologyDisabled(true)，条目保留、
Link.Disabled=true、Active=false。Active 正是为此存在：OfflineReassign()
只处理 Active 条目，所以停用的转发在 owner 掉线时不会被重新排队。

- 新增 UpdateTopologyDisabled / TopologyDisabled（照 UpdateTopologyGroup 的桥）
- 新增 store.ReconcileLinkDisabled 作接收端：adoption 时把环上的 flag 落进
  本地 store；本节点没有该转发时补一条 disabled 占位行（否则日后在本节点被
  claim 会复活），enable 则不建行
- SetTopologySync 由单向（store→环）扩为双向：群组仍上行，disabled 下行
- AddTopology 的 Active 跟随 Link.Disabled（原本硬编码 true，认领一个停用
  转发就会复活它）
- 审计日志细分 forward.stop / forward.start，与 forward.remove 区分

## 语义变更带出的两个新问题（都已修）

1. **「启动」这条路断了**。条目保留 ⇒ SubmitTask 被去重挡下，而认领路径的
   duplicate-claim 防御又会丢弃「已有 owner」的任务 ⇒ 重启任务发不出去，owner
   永远收不到，转发**能停不能起**。
   修：新增 Task.Restart 这一独立任务类型 + SubmitRestart + Handler.RestartFn，
   显式绕过 duplicate-claim 防御并原地复活（不重复建条目、不重跑 claim 簿记）。
   SubmitTask 的守卫同时从 HasTask 收窄为新的 HasActiveTask（跳过 disabled 条目
   与撤销任务）；saveCanvas 的判断相应改用 HasActiveTask，避免每次保存都对
   已标记的转发重复发撤销。

2. 原本两处 RemoveTopologyEntry 调用（ClaimFn/RevokeFn 的 disabled 分支）在
   新语义下会把本该保留的条目删掉，改为 UpdateTopologyDisabled。

## 测试（每个都做了「回退修复行→必须变红→还原变绿」双向验证）

- TestStoppedTopologyEntrySurvivesAdoption —— 离线成员也能学到停用，
  一次性 revoke 任务永远做不到这一点
- TestStoppedForwardNotRequeuedOnNodeDeparture / TestAddTopologyRespectsDisabledFlag
  —— 标记而非删除为何安全
- TestSubmitTaskNotBlockedByStoppedEntry / TestSubmitTaskStillDedupesActiveForward
- TestRestartTaskBypassesDuplicateClaimGuard / TestRestartFlagSurvivesTokenSerialization
- TestStopThenStartPublishesRestartTask（HTTP 端到端，断言**任务真的发出**）
- TestReconcileLinkDisabled*（store 侧三条）

★ 两次踩到**假绿**：第一版只断言 store 层（newTestHandler 的 Ring 为 nil，
坏掉的路根本没执行）；第二版在 re-enable **之后**才调 SubmitTask，此时新旧
谓词结果相同，测不出差异。都是靠「回退修复行看是否变红」抓出来的 —— 这个
双向验证已经是本项目的固定动作。

go build / go vet / go test ./... 全绿，gofmt 干净。

internal/httpapi/forward_revoke_test.go

@@ -117,3 +117,88 @@ func TestStopForwardPublishesDisabledFlagInRevokeTask(t *testing.T) {
 			"this stop was deliberate, which is the bug that let stopped forwards resurrect")
 	}
 }
+
+// TestStopThenStartPublishesRestartTask guards the failure mode that
+// mark-don't-remove introduces, and that only shows up on the WIRE.
+//
+// A stop keeps the topology entry (it is the carrier for the flag), so on
+// re-enable:
+//   - SubmitTask dedupes, because the entry exists;
+//   - the claim path discards any task for a forward that already has an owner.
+//
+// Both channels therefore refuse, no task is published, the owner never learns
+// about the re-enable, and the forward stays stopped forever — a forward the
+// user can stop but never restart.
+//
+// Asserting the task is PUBLISHED is the point: asserting only that the flag
+// cleared would pass while nothing reached the owner. (The earlier version of
+// this test did exactly that and stayed green against the broken code.)
+func TestStopThenStartPublishesRestartTask(t *testing.T) {
+	_, ring, ts := newRingTestHandler(t)
+
+	saveCanvas(t, ts, `{
+		"locals": [{"name":"svc","ip":"127.0.0.1","port":59999,"protocol":"tcp"}],
+		"remotes": [{"name":"srv-a","ip":"1.2.3.4","port":7000,"enabled":true}],
+		"links": [{"local":"svc","remote":"srv-a","remotePort":45999}]
+	}`)
+	// Claim it so a topology entry exists (that is what makes the two normal
+	// channels refuse later).
+	if _, err := ring.OnToken(context.Background(), &cluster.Token{Cycle: 1, State: *ring.State()}); err != nil {
+		t.Fatal(err)
+	}
+	if !ring.HasActiveTask("svc", "srv-a", 45999) {
+		t.Fatalf("precondition: forward should be active, topo=%+v", ring.State().TopologyList())
+	}
+
+	forwards := func(action string) {
+		t.Helper()
+		b, _ := json.Marshal(stopForwardReq{"svc", "srv-a", 45999})
+		req, _ := http.NewRequest(http.MethodPost, ts.URL+"/api/manager/forwards/"+action, bytes.NewReader(b))
+		req.SetBasicAuth("admin", "pw")
+		resp, err := ts.Client().Do(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp.Body.Close()
+		if resp.StatusCode != http.StatusOK {
+			t.Fatalf("%s status = %d", action, resp.StatusCode)
+		}
+	}
+
+	// --- stop: entry kept, marked disabled -------------------------------
+	forwards("stop")
+	if d, known := ring.TopologyDisabled("svc", "srv-a", 45999); !known || !d {
+		t.Fatalf("stop did not mark the topology entry disabled (known=%v disabled=%v)", known, d)
+	}
+	if ring.HasActiveTask("svc", "srv-a", 45999) {
+		t.Fatal("a stopped forward must not count as active")
+	}
+
+	// --- start: a task MUST reach the owner ------------------------------
+	forwards("start")
+	if d, _ := ring.TopologyDisabled("svc", "srv-a", 45999); d {
+		t.Fatal("start did not clear the disabled flag")
+	}
+	if !ring.HasActiveTask("svc", "srv-a", 45999) {
+		t.Fatal("after start the forward must be active again")
+	}
+
+	// The actual regression: something has to be queued for the owner. The
+	// re-enable must be published as a restart task, since a plain creation task
+	// would be deduped or discarded.
+	var restart *cluster.Task
+	for _, tk := range ring.State().PendingList() {
+		if tk.Restart && tk.Local.Name == "svc" && tk.Link.RemotePort == 45999 {
+			restart = tk
+			break
+		}
+	}
+	if restart == nil {
+		t.Fatalf("start published no restart task — the owner would never bring the "+
+			"worker back, leaving the forward permanently stopped (pending=%+v)",
+			ring.State().PendingList())
+	}
+	if restart.Link.Disabled {
+		t.Fatal("the restart task carries disabled=true, so the owner would re-apply the stop")
+	}
+}

internal/httpapi/handlers.go

@@ -245,7 +245,12 @@ func (h *Handler) applyCanvas(w http.ResponseWriter, r *http.Request, canvas *ca
 			}
 			if ln.Disabled {
 				// Stopped on the forwards page: make sure it leaves the topology.
-				if h.Ring.HasTask(ln.Local, ln.Remote, ln.RemotePort) {
+				// Guard on an ACTIVE task — an entry that is already marked
+				// disabled has nothing left to revoke, and re-issuing a revocation
+				// for it on every canvas save would be pure noise. (HasTask, which
+				// also matches disabled entries, is the right predicate for the
+				// "already handled" question this branch is not asking.)
+				if h.Ring.HasActiveTask(ln.Local, ln.Remote, ln.RemotePort) {
 					h.Ring.RevokeTask(loc, rem, ln)
 				}
 				continue

internal/httpapi/handlers_forwards.go

@@ -84,6 +84,25 @@ func (h *Handler) startForward(local, remote string, port int) error {
 		}
 		return nil
 	}
+	if h.Ring != nil {
+		// Publish the enable into the topology so it rides the ring (a peer that
+		// still holds the stale "stopped" copy learns about it on adoption).
+		h.Ring.UpdateTopologyDisabled(local, remote, port, false)
+	}
+	// A cluster forward whose topology entry still exists needs its OWNER to
+	// bring the worker back, and neither of the normal channels can do it:
+	//   - SubmitTask is idempotency-guarded, and the entry still exists (a stop
+	//     keeps it as the flag's carrier), so the submission is deduped away;
+	//   - the claim path drops any task for a forward that already has an
+	//     owner, as a defence against duplicate-claim collisions.
+	// So a re-enable of an existing entry is published as a dedicated RESTART
+	// task, which the owner applies unconditionally. Without it a forward the
+	// user can stop but not restart — which is what marking-instead-of-removing
+	// would otherwise have produced.
+	if h.Ring != nil && h.Ring.HasTopologyEntry(local, remote, port) {
+		h.Ring.SubmitRestart(loc, rem, ln)
+		return nil
+	}
 	if h.Ring != nil {
 		h.Ring.SubmitTask(loc, rem, ln)
 	}
@@ -119,6 +138,14 @@ func (h *Handler) stopForward(local, remote string, port int) error {
 	// SetLinkDisabled(true) above, so the link published into the token still
 	// carried disabled=false and got copied into the topology entry verbatim.
 	ln.Disabled = true
+	// Publish the stop into the topology BEFORE revoking: the revoke retires the
+	// own-side worker/entry, so the flag must already exist somewhere that
+	// survives it and travels the ring. This is the send half of cluster-wide
+	// disabled propagation (see store.ReconcileLinkDisabled for the receive
+	// half).
+	if h.Ring != nil {
+		h.Ring.UpdateTopologyDisabled(local, remote, port, true)
+	}
 	if loc.LocalOnly {
 		if h.Process != nil {
 			key := process.WorkerKey(local, remote, port)