diff --git a/api/proto/controlplane/v1/controlplane.proto b/api/proto/controlplane/v1/controlplane.proto
index 0ad8edd..1e8f963 100644
--- a/api/proto/controlplane/v1/controlplane.proto
+++ b/api/proto/controlplane/v1/controlplane.proto
@@ -235,6 +235,7 @@ message CheckTask {
   string password = 14;
   string credential_version = 15;
   uint32 max_attempts = 16;
+  string lease_token = 17;
 }
 
 enum CheckLevel {
@@ -260,6 +261,7 @@ message HealthObservation {
   google.protobuf.Duration latency = 8;
   string observed_egress_ip = 9;
   google.protobuf.Timestamp observed_at = 10;
+  string lease_token = 11;
 }
 
 message ReportObservationsResponse {
diff --git a/docs/api/control-plane.md b/docs/api/control-plane.md
index a33c83e..7f8da76 100644
--- a/docs/api/control-plane.md
+++ b/docs/api/control-plane.md
@@ -171,6 +171,9 @@ Routing 决定 AVAILABLE、SUSPECT 或 UNHEALTHY，并更新 Redis 活动池，
 检查层级、目标 Profile 与领取者一致，Reducer 成功后才确认任务；相同领取者对已确认
 任务的同一事实可重放，由活动池摘要幂等处理。当前生产配置尚未装配 Redis 共享 broker，
 因此无共享 broker 的服务会以 `Unavailable` 拒绝任务流，而不下发无租约任务。
+每次 Claim 还会签发新的不可预测 `lease_token`；Observation 必须回传该值。任务被重新
+领取后，旧 token 即使拥有相同 `task_id` 和 `checker_id` 也会被拒绝，避免过期实例的
+迟到事实覆盖新租约结果。
 
 `proxy-checker` 使用固定大小 worker-pool 执行每个 pull 批次，任务数不超过该请求的
 `max_in_flight`；每次尝试都受 `deadline` 和 `timeout` 的较小值约束，失败可在同一
diff --git a/docs/development/implementation-plan.md b/docs/development/implementation-plan.md
index d10ca09..e365702 100644
--- a/docs/development/implementation-plan.md
+++ b/docs/development/implementation-plan.md
@@ -281,7 +281,7 @@ Lua 同一原子边界归并，覆盖首次 CHECKING 失败进入 UNHEALTHY、AV
 Checker Observation 上报 RPC 已复用既有控制面监听接入 Controller：SPIFFE `checker` 身份、
 每批上限、配置阈值解析、代理归属查询与 Reducer 均已闭环。`StreamCheckTasks` 现已实现为
 有界 pull，并通过通用任务 broker 契约完成能力协商、同 Checker 并发窗口、租约到期回收、
-领取者栅栏和完成后重放；任务凭据仅由认证流在执行期下发。Redis 共享 due-index/租约持久化、
+领取者加不可预测 lease token 的栅栏和完成后重放；任务凭据仅由认证流在执行期下发。Redis 共享 due-index/租约持久化、
 生产 broker 已有契约但 Redis 实现尚未完成；`proxy-checker` 独立进程、固定大小 worker-pool、
 任务期重试/微批上报和 HTTP/HTTPS BASIC/TARGET 探测器已完成并有测试。SOCKS5、EGRESS
 专用出口探测、Redis due-index/跨副本租约和部署运行态仍未实现，因此本任务保持未完成。
diff --git a/gen/controlplane/v1/controlplane.pb.go b/gen/controlplane/v1/controlplane.pb.go
index 1077128..ba4cf73 100644
--- a/gen/controlplane/v1/controlplane.pb.go
+++ b/gen/controlplane/v1/controlplane.pb.go
@@ -1801,6 +1801,7 @@ type CheckTask struct {
 	Password          string `protobuf:"bytes,14,opt,name=password,proto3" json:"password,omitempty"`
 	CredentialVersion string `protobuf:"bytes,15,opt,name=credential_version,json=credentialVersion,proto3" json:"credential_version,omitempty"`
 	MaxAttempts       uint32 `protobuf:"varint,16,opt,name=max_attempts,json=maxAttempts,proto3" json:"max_attempts,omitempty"`
+	LeaseToken        string `protobuf:"bytes,17,opt,name=lease_token,json=leaseToken,proto3" json:"lease_token,omitempty"`
 	unknownFields     protoimpl.UnknownFields
 	sizeCache         protoimpl.SizeCache
 }
@@ -1947,6 +1948,13 @@ func (x *CheckTask) GetMaxAttempts() uint32 {
 	return 0
 }
 
+func (x *CheckTask) GetLeaseToken() string {
+	if x != nil {
+		return x.LeaseToken
+	}
+	return ""
+}
+
 type ObservationBatch struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	CheckerId     string                 `protobuf:"bytes,1,opt,name=checker_id,json=checkerId,proto3" json:"checker_id,omitempty"`
@@ -2011,6 +2019,7 @@ type HealthObservation struct {
 	Latency          *durationpb.Duration   `protobuf:"bytes,8,opt,name=latency,proto3" json:"latency,omitempty"`
 	ObservedEgressIp string                 `protobuf:"bytes,9,opt,name=observed_egress_ip,json=observedEgressIp,proto3" json:"observed_egress_ip,omitempty"`
 	ObservedAt       *timestamppb.Timestamp `protobuf:"bytes,10,opt,name=observed_at,json=observedAt,proto3" json:"observed_at,omitempty"`
+	LeaseToken       string                 `protobuf:"bytes,11,opt,name=lease_token,json=leaseToken,proto3" json:"lease_token,omitempty"`
 	unknownFields    protoimpl.UnknownFields
 	sizeCache        protoimpl.SizeCache
 }
@@ -2115,6 +2124,13 @@ func (x *HealthObservation) GetObservedAt() *timestamppb.Timestamp {
 	return nil
 }
 
+func (x *HealthObservation) GetLeaseToken() string {
+	if x != nil {
+		return x.LeaseToken
+	}
+	return ""
+}
+
 type ReportObservationsResponse struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	Accepted      uint32                 `protobuf:"varint,1,opt,name=accepted,proto3" json:"accepted,omitempty"`
@@ -2324,7 +2340,7 @@ const file_controlplane_v1_controlplane_proto_rawDesc = "" +
 	"\vinstance_id\x18\x02 \x01(\tR\n" +
 	"instanceId\x12\"\n" +
 	"\rmax_in_flight\x18\x03 \x01(\rR\vmaxInFlight\x12Q\n" +
-	"\x10supported_levels\x18\x04 \x03(\x0e2&.proxy_pool.controlplane.v1.CheckLevelR\x0fsupportedLevels\"\xde\x04\n" +
+	"\x10supported_levels\x18\x04 \x03(\x0e2&.proxy_pool.controlplane.v1.CheckLevelR\x0fsupportedLevels\"\xff\x04\n" +
 	"\tCheckTask\x12\x17\n" +
 	"\atask_id\x18\x01 \x01(\tR\x06taskId\x12\x19\n" +
 	"\bproxy_id\x18\x02 \x01(\tR\aproxyId\x12E\n" +
@@ -2344,11 +2360,13 @@ const file_controlplane_v1_controlplane_proto_rawDesc = "" +
 	"\busername\x18\r \x01(\tR\busername\x12\x1a\n" +
 	"\bpassword\x18\x0e \x01(\tR\bpassword\x12-\n" +
 	"\x12credential_version\x18\x0f \x01(\tR\x11credentialVersion\x12!\n" +
-	"\fmax_attempts\x18\x10 \x01(\rR\vmaxAttempts\"\x84\x01\n" +
+	"\fmax_attempts\x18\x10 \x01(\rR\vmaxAttempts\x12\x1f\n" +
+	"\vlease_token\x18\x11 \x01(\tR\n" +
+	"leaseToken\"\x84\x01\n" +
 	"\x10ObservationBatch\x12\x1d\n" +
 	"\n" +
 	"checker_id\x18\x01 \x01(\tR\tcheckerId\x12Q\n" +
-	"\fobservations\x18\x02 \x03(\v2-.proxy_pool.controlplane.v1.HealthObservationR\fobservations\"\xa6\x03\n" +
+	"\fobservations\x18\x02 \x03(\v2-.proxy_pool.controlplane.v1.HealthObservationR\fobservations\"\xc7\x03\n" +
 	"\x11HealthObservation\x12\x17\n" +
 	"\atask_id\x18\x01 \x01(\tR\x06taskId\x12\x19\n" +
 	"\bproxy_id\x18\x02 \x01(\tR\aproxyId\x12<\n" +
@@ -2362,7 +2380,9 @@ const file_controlplane_v1_controlplane_proto_rawDesc = "" +
 	"\x12observed_egress_ip\x18\t \x01(\tR\x10observedEgressIp\x12;\n" +
 	"\vobserved_at\x18\n" +
 	" \x01(\v2\x1a.google.protobuf.TimestampR\n" +
-	"observedAt\"T\n" +
+	"observedAt\x12\x1f\n" +
+	"\vlease_token\x18\v \x01(\tR\n" +
+	"leaseToken\"T\n" +
 	"\x1aReportObservationsResponse\x12\x1a\n" +
 	"\baccepted\x18\x01 \x01(\rR\baccepted\x12\x1a\n" +
 	"\brejected\x18\x02 \x01(\rR\brejected*\xc5\x01\n" +
diff --git a/internal/checker/controlplane/runner.go b/internal/checker/controlplane/runner.go
index eb35afe..6008c93 100644
--- a/internal/checker/controlplane/runner.go
+++ b/internal/checker/controlplane/runner.go
@@ -212,7 +212,7 @@ func (runner *Runner) executeTask(ctx context.Context, task *controlplanev1.Chec
 		result.FailureClass = probe.FailureProxyRequest
 	}
 	observation := &controlplanev1.HealthObservation{
-		TaskId: task.GetTaskId(), ProxyId: task.GetProxyId(), Level: task.GetLevel(), Success: result.Success,
+		TaskId: task.GetTaskId(), LeaseToken: task.GetLeaseToken(), ProxyId: task.GetProxyId(), Level: task.GetLevel(), Success: result.Success,
 		FailureClass: result.FailureClass, Latency: durationpb.New(result.Latency),
 		ObservedAt: timestamppb.New(runner.options.Now().UTC()),
 	}
diff --git a/internal/controller/health/grpc_handler.go b/internal/controller/health/grpc_handler.go
index 6714a98..c3952f8 100644
--- a/internal/controller/health/grpc_handler.go
+++ b/internal/controller/health/grpc_handler.go
@@ -146,7 +146,7 @@ func (handler *GRPCHandler) ReportObservations(
 			if now.IsZero() {
 				return nil, healthGRPCError(ErrInvalidGRPCHandler)
 			}
-			err = handler.options.TaskBroker.AuthorizeObservation(ctx, request.GetCheckerId(), observation, now)
+			err = handler.options.TaskBroker.AuthorizeObservation(ctx, request.GetCheckerId(), item.GetLeaseToken(), observation, now)
 		}
 		if err == nil {
 			_, err = handler.reducer.Apply(ctx, observation)
@@ -156,7 +156,7 @@ func (handler *GRPCHandler) ReportObservations(
 			if now.IsZero() {
 				return nil, healthGRPCError(ErrInvalidGRPCHandler)
 			}
-			err = handler.options.TaskBroker.CompleteObservation(ctx, request.GetCheckerId(), observation, now)
+			err = handler.options.TaskBroker.CompleteObservation(ctx, request.GetCheckerId(), item.GetLeaseToken(), observation, now)
 		}
 		if err == nil {
 			response.Accepted++
@@ -226,7 +226,7 @@ func healthGRPCError(err error) error {
 }
 
 func wireCheckTask(task LeasedTask, now time.Time) (*controlplanev1.CheckTask, error) {
-	if !validTaskIdentifier(task.TaskID) || !validTaskIdentifier(task.ProxyID) || task.Host == "" ||
+	if !validTaskIdentifier(task.TaskID) || !validTaskIdentifier(task.LeaseToken) || !validTaskIdentifier(task.ProxyID) || task.Host == "" ||
 		strings.TrimSpace(task.Host) != task.Host || task.Port == 0 || task.Attempts <= 0 || task.Attempts > math.MaxUint32 ||
 		!task.Deadline.After(now) || (task.SecretRef == "") != (task.CredentialVersion == "") {
 		return nil, ErrInvalidLeasedTask
@@ -249,7 +249,7 @@ func wireCheckTask(task LeasedTask, now time.Time) (*controlplanev1.CheckTask, e
 		return nil, ErrInvalidLeasedTask
 	}
 	return &controlplanev1.CheckTask{
-		TaskId: task.TaskID, ProxyId: task.ProxyID, Protocol: protocol, Host: task.Host, Port: uint32(task.Port),
+		TaskId: task.TaskID, LeaseToken: task.LeaseToken, ProxyId: task.ProxyID, Protocol: protocol, Host: task.Host, Port: uint32(task.Port),
 		SecretRef: task.SecretRef, CredentialVersion: task.CredentialVersion, Username: task.Username, Password: task.Password,
 		Level: level, RoutingName: task.RoutingName, TargetUrl: task.TargetURL,
 		Timeout: durationpb.New(task.Deadline.Sub(now)), Attempt: 1, MaxAttempts: uint32(task.Attempts),
diff --git a/internal/controller/health/grpc_handler_test.go b/internal/controller/health/grpc_handler_test.go
index 751ec61..5f2f6f4 100644
--- a/internal/controller/health/grpc_handler_test.go
+++ b/internal/controller/health/grpc_handler_test.go
@@ -151,17 +151,21 @@ func TestGRPCHandlerStreamsLeasedTasksAndFencesReportedFacts(t *testing.T) {
 	if _, err := stream.Recv(); !errors.Is(err, io.EOF) {
 		t.Fatalf("second Recv() error = %v, want EOF", err)
 	}
+	acceptedObservation := grpcHealthObservation(task.GetTaskId(), controlplanev1.CheckLevel_CHECK_LEVEL_BASIC, now.Add(time.Second))
+	acceptedObservation.LeaseToken = task.GetLeaseToken()
 	response, err := client.ReportObservations(context.Background(), &controlplanev1.ObservationBatch{
 		CheckerId: "checker-a", Observations: []*controlplanev1.HealthObservation{
-			grpcHealthObservation(task.GetTaskId(), controlplanev1.CheckLevel_CHECK_LEVEL_BASIC, now.Add(time.Second)),
+			acceptedObservation,
 		},
 	})
 	if err != nil || response.GetAccepted() != 1 || len(global.commands) != 1 {
 		t.Fatalf("ReportObservations() = (%+v, %v), global=%d", response, err, len(global.commands))
 	}
+	rejectedObservation := grpcHealthObservation(task.GetTaskId(), controlplanev1.CheckLevel_CHECK_LEVEL_BASIC, now.Add(time.Second))
+	rejectedObservation.LeaseToken = task.GetLeaseToken()
 	rejected, err := client.ReportObservations(context.Background(), &controlplanev1.ObservationBatch{
 		CheckerId: "checker-b", Observations: []*controlplanev1.HealthObservation{
-			grpcHealthObservation(task.GetTaskId(), controlplanev1.CheckLevel_CHECK_LEVEL_BASIC, now.Add(time.Second)),
+			rejectedObservation,
 		},
 	})
 	if err != nil || rejected.GetRejected() != 1 || len(global.commands) != 1 {
diff --git a/internal/controller/health/task_broker.go b/internal/controller/health/task_broker.go
index 57c78fd..377edbb 100644
--- a/internal/controller/health/task_broker.go
+++ b/internal/controller/health/task_broker.go
@@ -2,6 +2,7 @@ package health
 
 import (
 	"context"
+	"crypto/rand"
 	"crypto/sha256"
 	"encoding/hex"
 	"errors"
@@ -73,6 +74,7 @@ type TaskClaim struct {
 // for the duration of a task lease and must not be logged.
 type LeasedTask struct {
 	TaskID            string
+	LeaseToken        string
 	ProxyID           string
 	Protocol          proxyDomain.Scheme
 	Host              string
@@ -98,8 +100,8 @@ func (LeasedTask) Format(state fmt.State, _ rune) {
 type TaskBroker interface {
 	TaskSink
 	Claim(context.Context, TaskClaim) ([]LeasedTask, error)
-	AuthorizeObservation(context.Context, string, healthDomain.Observation, time.Time) error
-	CompleteObservation(context.Context, string, healthDomain.Observation, time.Time) error
+	AuthorizeObservation(context.Context, string, string, healthDomain.Observation, time.Time) error
+	CompleteObservation(context.Context, string, string, healthDomain.Observation, time.Time) error
 }
 
 type MemoryTaskBrokerOptions struct {
@@ -127,11 +129,13 @@ type brokerTask struct {
 type taskLease struct {
 	checkerID  string
 	instanceID string
+	token      string
 	expiresAt  time.Time
 }
 
 type taskCompletion struct {
 	checkerID string
+	token     string
 	expiresAt time.Time
 }
 
@@ -218,6 +222,7 @@ func (broker *MemoryTaskBroker) Claim(ctx context.Context, claim TaskClaim) ([]L
 		return []LeasedTask{}, nil
 	}
 	materials := make([]TaskMaterial, len(taskIDs))
+	tokens := make([]string, len(taskIDs))
 	for index, taskID := range taskIDs {
 		material, resolveErr := broker.options.Material.ResolveCheckTask(ctx, broker.tasks[taskID].plan.Candidate)
 		if resolveErr != nil {
@@ -227,6 +232,11 @@ func (broker *MemoryTaskBroker) Claim(ctx context.Context, claim TaskClaim) ([]L
 			return nil, ErrInvalidLeasedTask
 		}
 		materials[index] = material
+		leaseToken, tokenErr := newLeaseToken()
+		if tokenErr != nil {
+			return nil, tokenErr
+		}
+		tokens[index] = leaseToken
 	}
 	result := make([]LeasedTask, len(taskIDs))
 	for index, taskID := range taskIDs {
@@ -235,8 +245,9 @@ func (broker *MemoryTaskBroker) Claim(ctx context.Context, claim TaskClaim) ([]L
 		if plan.Deadline.Before(leaseUntil) {
 			leaseUntil = plan.Deadline
 		}
-		broker.leases[taskID] = taskLease{checkerID: claim.CheckerID, instanceID: claim.InstanceID, expiresAt: leaseUntil}
-		result[index] = leasedTask(taskID, plan, materials[index])
+		leaseToken := tokens[index]
+		broker.leases[taskID] = taskLease{checkerID: claim.CheckerID, instanceID: claim.InstanceID, token: leaseToken, expiresAt: leaseUntil}
+		result[index] = leasedTask(taskID, leaseToken, plan, materials[index])
 	}
 	return result, nil
 }
@@ -244,10 +255,11 @@ func (broker *MemoryTaskBroker) Claim(ctx context.Context, claim TaskClaim) ([]L
 func (broker *MemoryTaskBroker) AuthorizeObservation(
 	ctx context.Context,
 	checkerID string,
+	leaseToken string,
 	observation healthDomain.Observation,
 	now time.Time,
 ) error {
-	if ctx == nil || broker == nil || !validTaskIdentifier(checkerID) || now.IsZero() {
+	if ctx == nil || broker == nil || !validTaskIdentifier(checkerID) || !validTaskIdentifier(leaseToken) || now.IsZero() {
 		return ErrInvalidTaskBroker
 	}
 	if err := ctx.Err(); err != nil {
@@ -259,16 +271,17 @@ func (broker *MemoryTaskBroker) AuthorizeObservation(
 	}
 	broker.mu.Lock()
 	defer broker.mu.Unlock()
-	return broker.authorizeObservationLocked(checkerID, normalized, now.UTC())
+	return broker.authorizeObservationLocked(checkerID, leaseToken, normalized, now.UTC())
 }
 
 func (broker *MemoryTaskBroker) CompleteObservation(
 	ctx context.Context,
 	checkerID string,
+	leaseToken string,
 	observation healthDomain.Observation,
 	now time.Time,
 ) error {
-	if ctx == nil || broker == nil || !validTaskIdentifier(checkerID) || now.IsZero() {
+	if ctx == nil || broker == nil || !validTaskIdentifier(checkerID) || !validTaskIdentifier(leaseToken) || now.IsZero() {
 		return ErrInvalidTaskBroker
 	}
 	if err := ctx.Err(); err != nil {
@@ -281,7 +294,7 @@ func (broker *MemoryTaskBroker) CompleteObservation(
 	now = now.UTC()
 	broker.mu.Lock()
 	defer broker.mu.Unlock()
-	if err := broker.authorizeObservationLocked(checkerID, normalized, now); err != nil {
+	if err := broker.authorizeObservationLocked(checkerID, leaseToken, normalized, now); err != nil {
 		return err
 	}
 	if _, complete := broker.finished[normalized.TaskID]; complete {
@@ -289,12 +302,13 @@ func (broker *MemoryTaskBroker) CompleteObservation(
 	}
 	task := broker.tasks[normalized.TaskID]
 	delete(broker.leases, normalized.TaskID)
-	broker.finished[normalized.TaskID] = taskCompletion{checkerID: checkerID, expiresAt: task.plan.Deadline}
+	broker.finished[normalized.TaskID] = taskCompletion{checkerID: checkerID, token: leaseToken, expiresAt: task.plan.Deadline}
 	return nil
 }
 
 func (broker *MemoryTaskBroker) authorizeObservationLocked(
 	checkerID string,
+	leaseToken string,
 	observation healthDomain.Observation,
 	now time.Time,
 ) error {
@@ -307,7 +321,7 @@ func (broker *MemoryTaskBroker) authorizeObservationLocked(
 		return ErrTaskObservation
 	}
 	if finished, complete := broker.finished[observation.TaskID]; complete {
-		if finished.checkerID != checkerID {
+		if finished.checkerID != checkerID || finished.token != leaseToken {
 			return ErrTaskLeaseNotOwned
 		}
 		return nil
@@ -316,7 +330,7 @@ func (broker *MemoryTaskBroker) authorizeObservationLocked(
 	if !leased || !lease.expiresAt.After(now) {
 		return ErrTaskLeaseExpired
 	}
-	if lease.checkerID != checkerID {
+	if lease.checkerID != checkerID || lease.token != leaseToken {
 		return ErrTaskLeaseNotOwned
 	}
 	return nil
@@ -445,15 +459,23 @@ func deterministicTaskID(task PlannedTask) string {
 	return "check_" + hex.EncodeToString(digest[:])
 }
 
-func leasedTask(taskID string, plan PlannedTask, material TaskMaterial) LeasedTask {
+func leasedTask(taskID, leaseToken string, plan PlannedTask, material TaskMaterial) LeasedTask {
 	return LeasedTask{
-		TaskID: taskID, ProxyID: plan.Candidate.ProxyID, Protocol: material.Protocol, Host: material.Host, Port: material.Port,
+		TaskID: taskID, LeaseToken: leaseToken, ProxyID: plan.Candidate.ProxyID, Protocol: material.Protocol, Host: material.Host, Port: material.Port,
 		SecretRef: material.SecretRef, CredentialVersion: material.CredentialVersion, Username: material.Username, Password: material.Password,
 		Level: plan.Candidate.Level, RoutingName: plan.Candidate.RoutingName, TargetURL: plan.Candidate.TargetURL,
 		Deadline: plan.Deadline.UTC(), Attempts: plan.Attempts,
 	}
 }
 
+func newLeaseToken() (string, error) {
+	var entropy [24]byte
+	if _, err := rand.Read(entropy[:]); err != nil {
+		return "", err
+	}
+	return "lease_" + hex.EncodeToString(entropy[:]), nil
+}
+
 func taskMatchesObservation(task PlannedTask, observation healthDomain.Observation) bool {
 	return task.Candidate.ProxyID == observation.ProxyID && task.Candidate.Level == observation.Level &&
 		task.Candidate.RoutingName == observation.RoutingName && task.Candidate.TargetURL == observation.TargetURL
diff --git a/internal/controller/health/task_broker_test.go b/internal/controller/health/task_broker_test.go
index 814721f..92cf40b 100644
--- a/internal/controller/health/task_broker_test.go
+++ b/internal/controller/health/task_broker_test.go
@@ -42,16 +42,16 @@ func TestMemoryTaskBrokerClaimsSupportedTasksAndFencesObservations(t *testing.T)
 		TaskID: claimed[0].TaskID, ProxyID: "basic", Level: healthDomain.LevelBasic,
 		Success: true, Latency: time.Millisecond, ObservedAt: now.Add(time.Second),
 	}
-	if err := broker.AuthorizeObservation(context.Background(), "checker-b", observation, now.Add(time.Second)); !errors.Is(err, ErrTaskLeaseNotOwned) {
+	if err := broker.AuthorizeObservation(context.Background(), "checker-b", claimed[0].LeaseToken, observation, now.Add(time.Second)); !errors.Is(err, ErrTaskLeaseNotOwned) {
 		t.Fatalf("AuthorizeObservation(other checker) error = %v, want ErrTaskLeaseNotOwned", err)
 	}
-	if err := broker.AuthorizeObservation(context.Background(), "checker-a", observation, now.Add(time.Second)); err != nil {
+	if err := broker.AuthorizeObservation(context.Background(), "checker-a", claimed[0].LeaseToken, observation, now.Add(time.Second)); err != nil {
 		t.Fatalf("AuthorizeObservation(owner): %v", err)
 	}
-	if err := broker.CompleteObservation(context.Background(), "checker-a", observation, now.Add(time.Second)); err != nil {
+	if err := broker.CompleteObservation(context.Background(), "checker-a", claimed[0].LeaseToken, observation, now.Add(time.Second)); err != nil {
 		t.Fatalf("CompleteObservation(): %v", err)
 	}
-	if err := broker.AuthorizeObservation(context.Background(), "checker-a", observation, now.Add(2*time.Second)); err != nil {
+	if err := broker.AuthorizeObservation(context.Background(), "checker-a", claimed[0].LeaseToken, observation, now.Add(2*time.Second)); err != nil {
 		t.Fatalf("AuthorizeObservation(replay): %v", err)
 	}
 }
@@ -82,7 +82,7 @@ func TestMemoryTaskBrokerReclaimsExpiredLeaseWithoutExceedingCheckerLimit(t *tes
 	}
 	now = now.Add(2 * time.Second)
 	reclaimed, err := broker.Claim(context.Background(), TaskClaim{CheckerID: "checker-b", InstanceID: "instance-b", MaxInFlight: 1, SupportedLevels: []healthDomain.Level{healthDomain.LevelBasic}})
-	if err != nil || len(reclaimed) != 1 || reclaimed[0].TaskID != first[0].TaskID {
+	if err != nil || len(reclaimed) != 1 || reclaimed[0].TaskID != first[0].TaskID || reclaimed[0].LeaseToken == first[0].LeaseToken {
 		t.Fatalf("reclaimed Claim() = (%+v, %v)", reclaimed, err)
 	}
 }