feat: dispatch using gateway routing strategies

README.md

@@ -45,8 +45,8 @@ Proxy Pool 用 Controller 协调这些变化，并让 Gateway 数据面只消费
   Runtime 会话组件已有实现与定向测试。`SessionSupervisor` 会为可恢复控制面中断执行
   有界退避重连。Controller 可向 Worker 下发无凭据引用的已归属 Proxy 及 Gateway
   Routing 快照。Gateway 会将 Routing 与 Proxy 原子编译为同一内存 View，并只按当前未过期
-  View 匹配请求；`proxy-gateway` 命令、凭据分发，以及策略选择与 `onUnavailable` 派发语义
-  仍待装配。
+  View 匹配请求，并在内存中按 Sequential、Random、Round Robin、Weighted 或 Least
+  Connections 选择上游；`proxy-gateway` 命令、凭据分发和 `onUnavailable` 派发语义仍待装配。
 - **安全边界**：Gateway、Distribution 与 Admin 使用各自的认证语义，并支持
   CIDR、可信代理、严格请求解析和敏感信息最小化。
 
@@ -85,9 +85,8 @@ flowchart LR
   Redis 会话栅栏。
 - **部分完成**：Gateway 传输与调度组件、Snapshot 本地存储、Worker ownership
   与运行态领域组件、Docker Compose/Kubernetes 静态部署清单和 protobuf 契约。
-- **待完成**：带凭据 Proxy 分发、Gateway 进程装配、Routing 策略选择与
-  `onUnavailable`、Outcome 上报、Checker 调度与健康状态链，以及 loadgen 和代表性
-  集群压测。
+- **待完成**：带凭据 Proxy 分发、Gateway 进程装配、`onUnavailable`、Outcome 上报、
+  Checker 调度与健康状态链，以及 loadgen 和代表性集群压测。
 
 检查项数量不等于生产就绪度。静态部署清单与 protobuf descriptor 验证也不代表
 端到端拓扑已经完成；`100,000 QPS` 仍只是待验证的集群设计目标。

docs/api/control-plane.md

@@ -31,8 +31,9 @@ Gateway 校验后 ACK 并开始 Runtime 心跳。Controller 会从 Redis 的有
 `usable_until`；带凭据 Proxy 会 fail-closed，直到凭据材料分发完成。完整 Snapshot
 已从配置原始顺序和 Admin 当前状态合成 Gateway Routing，并与 Proxy 一起纳入 checksum；
 Gateway 已将该 payload 编译并原子发布到与 Proxy 相同版本的本地 View，动态 Router 只匹配
-当前未过期 View。策略选择、`onUnavailable`、增量、Gateway 进程装配、Outcome 与 Checker
-闭环尚未实现。`ReportOutcomes` 仍明确返回 `Unimplemented`；`100,000 QPS` 仍是未验证的设计目标。
+当前未过期 View；派发器已按五种策略从该 View 选择上游，且在 Proxy 容量耗尽时只在该
+View 的其余候选中回退。`onUnavailable`、增量、Gateway 进程装配、Outcome 与 Checker 闭环
+尚未实现。`ReportOutcomes` 仍明确返回 `Unimplemented`；`100,000 QPS` 仍是未验证的设计目标。
 
 `WatchSnapshots` 建立时校验当前 session；每次签发快照引用时也把 `session_id`
 交给 Redis 原子校验。重复 Register 会同时清除旧 Runtime 和已签发引用，因此迟到的

docs/development/implementation-plan.md

@@ -220,6 +220,7 @@ Snapshot 的 `valid_until` 到达时结束流；公用 `SessionSupervisor` 已
 提供可恢复错误的有界指数退避重连，并在参数/认证/协议错误时停止。Gateway Routing
 payload 已按配置顺序和 Admin revision/current 状态发布并覆盖 checksum；Gateway 已将其与
 Proxy 原子编译为同版本 View，动态 Router 只匹配该未过期 View。策略选择、`onUnavailable`、
+派发器的五种上游选择已接入该 View，并在容量耗尽时在同版本候选中回退；`onUnavailable`、
 凭据分发、Gateway 命令与 Outcome 上报仍未实现。
 
 已新增公用 `domain/activitypool` 契约及并发安全内存参考实现，Provider

docs/requirements/completion-audit.md

@@ -100,13 +100,13 @@ CI 已配置 Linux race job。PostgreSQL 18 和 Redis 8.2 的隔离 Adapter fixt
    SPIFFE mTLS 校验和 Controller 生命周期接线已完成；Redis Provider Leader、
    分布式请求额度、Distribution Client 限制和 Provider 状态丢失重建已完成。
 6. Worker 基础网络快照流、无凭据引用 Proxy/Gateway Routing payload、Gateway Snapshot
-   客户端及同版本 Routing 编译/动态匹配已完成；策略选择、`onUnavailable`、凭据分发与
-   Outcome 上报仍待完成。Redis ownership drain/ACK/过期回收及按 Worker 的可下发索引已完成。
+   客户端、同版本 Routing 编译/动态匹配和五种策略上游选择已完成；`onUnavailable`、凭据
+   分发与 Outcome 上报仍待完成。Redis ownership drain/ACK/过期回收及按 Worker 的可下发索引已完成。
 7. Checker 调度、探测器和健康 reducer。
 8. Admin/Distribution 细粒度授权和审计查询；Distribution 分布式限流已完成。
 9. 真实 Compose/Kubernetes 集成、故障演练和代表性集群负载测试。
-10. 将五种 Routing 策略和 `onUnavailable` 接入 Gateway/Distribution 运行链，
-    补齐 Sequential 持久化恢复、跨实例 CAS 和 disabled candidate 语义。
+10. 将 `onUnavailable` 接入 Gateway/Distribution 运行链，补齐 Sequential 持久化恢复、
+    跨实例 CAS 和 disabled candidate 语义。
 11. 补齐 Proxy Capacity 动态降容契约、Reservation 全生命周期观测；短 TTL
     Proxy 的零计数运行态已在后续 Snapshot Apply 中回收。
 

docs/requirements/traceability.md

@@ -19,7 +19,7 @@
 |---|---|---|---|
 | ROUTE-001 | Routing 自上而下匹配，首条命中停止 | 3534-3798, 5825-6467 | `rule.go` 与不可变/首命中单测 |
 | ROUTE-002 | Routing 与 Upstream 生命周期解耦 | 3534-3798 | 包依赖与配置模型 |
-| ROUTE-003 | 支持 sequential、random、roundRobin、weighted、leastConnections | 5825-6467 | 五种领域策略及单测已完成；配置到 Gateway/Distribution 运行链的接线待完成 |
+| ROUTE-003 | 支持 sequential、random、roundRobin、weighted、leastConnections | 5825-6467 | 五种领域策略、同版本 Gateway Snapshot 派发和定向测试已完成；Distribution 接线待完成 |
 | ROUTE-004 | Sequential 连续空结果达到阈值后原子切换一次 | 5295-5824, 6520-6617 | 进程内 `RoutingCursor` 版本 CAS 与 100 并发测试已完成；持久化恢复和跨实例 CAS 待完成 |
 | ROUTE-005 | 空计数属于 Upstream，当前选择属于 Routing | 8442-8529 | 共享 `UpstreamEmptyState` 双 Routing 测试 |
 | ROUTE-006 | 旧 Upstream 已有 Proxy 继续耗尽，不因切换直接丢弃 | 6618-6641 | 通用 ownership Drain/ACK 原语已测试；Routing 切换到 Drain 的编排待完成 |

internal/domain/routing/strategy.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"math/rand"
 	"sync"
+	"sync/atomic"
 )
 
 var ErrNoCandidate = errors.New("no eligible routing candidate")
@@ -24,7 +25,7 @@ type RandomSource interface {
 }
 
 type randomSelector struct {
-	source *synchronizedRandomSource
+	source RandomSource
 }
 
 type globalRandomSource struct{}
@@ -73,8 +74,7 @@ func (s *randomSelector) Select(candidates []Candidate) (Candidate, error) {
 }
 
 type roundRobinSelector struct {
-	mu   sync.Mutex
-	next int
+	next atomic.Uint64
 }
 
 func NewRoundRobin() Selector {
@@ -86,22 +86,36 @@ func (s *roundRobinSelector) Select(candidates []Candidate) (Candidate, error) {
 		return Candidate{}, ErrNoCandidate
 	}
 
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	start := s.next % len(candidates)
-	for offset := range len(candidates) {
-		selected := (start + offset) % len(candidates)
-		if !candidates[selected].Eligible {
-			continue
+	for {
+		next := s.next.Load()
+		start := int(next % uint64(len(candidates)))
+		for offset := range len(candidates) {
+			selected := (start + offset) % len(candidates)
+			if !candidates[selected].Eligible {
+				continue
+			}
+			if s.next.CompareAndSwap(next, uint64(selected+1)) {
+				return candidates[selected], nil
+			}
+			break
+		}
+		if allCandidatesIneligible(candidates) {
+			return Candidate{}, ErrNoCandidate
 		}
-		s.next = (selected + 1) % len(candidates)
-		return candidates[selected], nil
 	}
-	return Candidate{}, ErrNoCandidate
+}
+
+func allCandidatesIneligible(candidates []Candidate) bool {
+	for _, candidate := range candidates {
+		if candidate.Eligible {
+			return false
+		}
+	}
+	return true
 }
 
 type weightedSelector struct {
-	source *synchronizedRandomSource
+	source RandomSource
 }
 
 func NewWeighted(source ...RandomSource) Selector {
@@ -159,10 +173,9 @@ func (leastConnectionsSelector) Select(candidates []Candidate) (Candidate, error
 	return selected, nil
 }
 
-func newSynchronizedRandomSource(sources []RandomSource) *synchronizedRandomSource {
-	var source RandomSource = globalRandomSource{}
-	if len(sources) > 0 && sources[0] != nil {
-		source = sources[0]
+func newSynchronizedRandomSource(sources []RandomSource) RandomSource {
+	if len(sources) == 0 || sources[0] == nil {
+		return globalRandomSource{}
 	}
-	return &synchronizedRandomSource{source: source}
+	return &synchronizedRandomSource{source: sources[0]}
 }

internal/gateway/dispatch/dispatcher.go

@@ -2,6 +2,7 @@ package dispatch
 
 import (
 	"errors"
+	"sync"
 	"sync/atomic"
 	"time"
 
@@ -36,12 +37,24 @@ func (l *Lease) Cancel() error  { return l.reserved.Cancel() }
 func (l *Lease) Release() error { return l.reserved.Release() }
 
 type Dispatcher struct {
-	store  *snapshot.Store
-	cursor atomic.Uint64
+	store        *snapshot.Store
+	cursor       atomic.Uint64
+	random       routing.RandomSource
+	routingState atomic.Pointer[routingSelectorState]
 }
 
-func New(store *snapshot.Store) *Dispatcher {
-	return &Dispatcher{store: store}
+type routingSelectorState struct {
+	epoch     uint64
+	version   uint64
+	selectors sync.Map
+}
+
+func New(store *snapshot.Store, randomSources ...routing.RandomSource) *Dispatcher {
+	dispatcher := &Dispatcher{store: store}
+	if len(randomSources) > 0 {
+		dispatcher.random = randomSources[0]
+	}
+	return dispatcher
 }
 
 func (d *Dispatcher) Acquire(request Request) (*Lease, error) {
@@ -55,11 +68,121 @@ func (d *Dispatcher) Acquire(request Request) (*Lease, error) {
 	if request.Now.IsZero() {
 		request.Now = time.Now().UTC()
 	}
+	if request.Strategy.Type != "" {
+		return d.acquireRouted(view, request)
+	}
+	return d.acquireFromUpstreams(view, request, request.Upstreams)
+}
+
+func (d *Dispatcher) acquireRouted(view *snapshot.View, request Request) (*Lease, error) {
+	if request.Strategy.Type == routing.StrategySequential {
+		if request.Strategy.CurrentUpstream == "" {
+			return nil, ErrNoCandidate
+		}
+		return d.acquireFromUpstreams(view, request, []string{request.Strategy.CurrentUpstream})
+	}
+	candidates, err := d.routingCandidates(view, request)
+	if err != nil {
+		return nil, ErrNoCandidate
+	}
+	selector, err := d.routingSelector(view, request)
+	if err != nil {
+		return nil, ErrNoCandidate
+	}
+	for range candidates {
+		candidate, selectErr := selector.Select(candidates)
+		if selectErr != nil {
+			return nil, ErrNoCandidate
+		}
+		lease, acquireErr := d.acquireFromUpstreams(view, request, []string{candidate.Name})
+		if acquireErr == nil {
+			return lease, nil
+		}
+		for index := range candidates {
+			if candidates[index].Name == candidate.Name {
+				candidates[index].Eligible = false
+				break
+			}
+		}
+	}
+	return nil, ErrNoCandidate
+}
+
+func (d *Dispatcher) routingCandidates(view *snapshot.View, request Request) ([]routing.Candidate, error) {
+	if len(request.Upstreams) == 0 {
+		return nil, ErrNoCandidate
+	}
+	result := make([]routing.Candidate, 0, len(request.Upstreams))
+	seen := make(map[string]struct{}, len(request.Upstreams))
+	for _, upstream := range request.Upstreams {
+		if upstream == "" {
+			return nil, ErrNoCandidate
+		}
+		if _, duplicate := seen[upstream]; duplicate {
+			return nil, ErrNoCandidate
+		}
+		seen[upstream] = struct{}{}
+		candidate := routing.Candidate{Name: upstream, Eligible: true}
+		switch request.Strategy.Type {
+		case routing.StrategyWeighted:
+			weight, exists := request.Strategy.Weights[upstream]
+			if !exists || weight == 0 || uint64(weight) > uint64(maxInt()) {
+				return nil, ErrNoCandidate
+			}
+			candidate.Weight = int(weight)
+		case routing.StrategyLeastConnections:
+			candidate.Active, candidate.Eligible = view.UpstreamLoad(snapshot.Query{
+				Now: request.Now, Scheme: request.Scheme, RequiredTags: request.RequiredTags,
+				Exclude: request.Exclude, SafetyMargin: request.SafetyMargin,
+			}, upstream)
+		}
+		result = append(result, candidate)
+	}
+	return result, nil
+}
+
+func (d *Dispatcher) routingSelector(view *snapshot.View, request Request) (routing.Selector, error) {
+	state := d.selectorState(view)
+	key := request.RoutingName + "\x00" + string(request.Strategy.Type)
+	if existing, found := state.selectors.Load(key); found {
+		return existing.(routing.Selector), nil
+	}
+	var selector routing.Selector
+	switch request.Strategy.Type {
+	case routing.StrategyRandom:
+		selector = routing.NewRandom(d.random)
+	case routing.StrategyRoundRobin:
+		selector = routing.NewRoundRobin()
+	case routing.StrategyWeighted:
+		selector = routing.NewWeighted(d.random)
+	case routing.StrategyLeastConnections:
+		selector = routing.NewLeastConnections()
+	default:
+		return nil, ErrNoCandidate
+	}
+	actual, _ := state.selectors.LoadOrStore(key, selector)
+	return actual.(routing.Selector), nil
+}
+
+func (d *Dispatcher) selectorState(view *snapshot.View) *routingSelectorState {
+	for {
+		current := d.routingState.Load()
+		if current != nil && current.epoch == view.Epoch && current.version == view.Version {
+			return current
+		}
+		next := &routingSelectorState{epoch: view.Epoch, version: view.Version}
+		if d.routingState.CompareAndSwap(current, next) {
+			return next
+		}
+	}
+}
+
+func (d *Dispatcher) acquireFromUpstreams(view *snapshot.View, request Request, upstreams []string) (*Lease, error) {
 
 	selection := view.Select(snapshot.Query{
 		Now:          request.Now,
 		Scheme:       request.Scheme,
-		Upstreams:    request.Upstreams,
+		Upstreams:    upstreams,
 		RequiredTags: request.RequiredTags,
 		Exclude:      request.Exclude,
 		SafetyMargin: request.SafetyMargin,
@@ -87,3 +210,7 @@ func (d *Dispatcher) Acquire(request Request) (*Lease, error) {
 	}
 	return nil, ErrNoCandidate
 }
+
+func maxInt() int {
+	return int(^uint(0) >> 1)
+}

internal/gateway/dispatch/dispatcher_test.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	proxyDomain "proxy-pool/internal/domain/proxy"
+	"proxy-pool/internal/domain/routing"
 	"proxy-pool/internal/gateway/snapshot"
 )
 
@@ -112,6 +113,185 @@ func TestAcquireNeverOversubscribesSnapshotProxy(t *testing.T) {
 	}
 }
 
+func TestAcquireUsesSequentialCurrentUpstream(t *testing.T) {
+	store := routingStrategyStore(t)
+	dispatcher := New(store)
+	lease, err := dispatcher.Acquire(Request{
+		Now: time.Now(), RoutingName: "sequential", Upstreams: []string{"upstream-a", "upstream-b"},
+		Strategy: routing.Strategy{Type: routing.StrategySequential, CurrentUpstream: "upstream-b"},
+	})
+	if err != nil {
+		t.Fatalf("Acquire(): %v", err)
+	}
+	if lease.Proxy.SourceUpstream != "upstream-b" {
+		t.Fatalf("selected upstream = %q, want upstream-b", lease.Proxy.SourceUpstream)
+	}
+	if err := lease.Cancel(); err != nil {
+		t.Fatalf("Cancel(): %v", err)
+	}
+}
+
+func TestAcquireRoundRobinCyclesRoutingUpstreams(t *testing.T) {
+	store := routingStrategyStore(t)
+	dispatcher := New(store)
+	request := Request{
+		Now: time.Now(), RoutingName: "round-robin", Upstreams: []string{"upstream-a", "upstream-b"},
+		Strategy: routing.Strategy{Type: routing.StrategyRoundRobin},
+	}
+	for index, want := range []string{"upstream-a", "upstream-b", "upstream-a"} {
+		lease, err := dispatcher.Acquire(request)
+		if err != nil {
+			t.Fatalf("Acquire(%d): %v", index, err)
+		}
+		if lease.Proxy.SourceUpstream != want {
+			t.Fatalf("Acquire(%d) upstream = %q, want %q", index, lease.Proxy.SourceUpstream, want)
+		}
+		if err := lease.Cancel(); err != nil {
+			t.Fatalf("Cancel(%d): %v", index, err)
+		}
+	}
+}
+
+func TestAcquireResetsRoundRobinStateWhenSnapshotVersionChanges(t *testing.T) {
+	store := routingStrategyStore(t)
+	dispatcher := New(store)
+	request := Request{
+		Now: time.Now(), RoutingName: "round-robin", Upstreams: []string{"upstream-a", "upstream-b"},
+		Strategy: routing.Strategy{Type: routing.StrategyRoundRobin},
+	}
+	first, err := dispatcher.Acquire(request)
+	if err != nil {
+		t.Fatalf("Acquire(first): %v", err)
+	}
+	if first.Proxy.SourceUpstream != "upstream-a" {
+		t.Fatalf("first upstream = %q, want upstream-a", first.Proxy.SourceUpstream)
+	}
+	if err := first.Cancel(); err != nil {
+		t.Fatalf("Cancel(first): %v", err)
+	}
+
+	next := snapshot.Envelope{
+		ClusterID: "cluster-a", WorkerID: "worker-a", Epoch: 1, Version: 2, Full: true,
+		Proxies: []proxyDomain.Proxy{
+			{ID: "proxy-a", Scheme: proxyDomain.SchemeHTTP, SourceUpstream: "upstream-a", State: proxyDomain.StateAvailable, MaxConcurrency: 1},
+			{ID: "proxy-b", Scheme: proxyDomain.SchemeHTTP, SourceUpstream: "upstream-b", State: proxyDomain.StateAvailable, MaxConcurrency: 1},
+		},
+	}
+	next.Checksum = snapshot.Checksum(next.Proxies)
+	if err := store.Apply(next); err != nil {
+		t.Fatalf("Apply(next): %v", err)
+	}
+	second, err := dispatcher.Acquire(request)
+	if err != nil {
+		t.Fatalf("Acquire(second): %v", err)
+	}
+	if second.Proxy.SourceUpstream != "upstream-a" {
+		t.Fatalf("second upstream = %q, want reset upstream-a", second.Proxy.SourceUpstream)
+	}
+	if err := second.Cancel(); err != nil {
+		t.Fatalf("Cancel(second): %v", err)
+	}
+}
+
+func TestAcquireFallsBackWhenSelectedRoutingUpstreamIsFull(t *testing.T) {
+	store := routingStrategyStore(t)
+	var held *proxyDomain.Reservation
+	for _, entry := range store.Current().Entries {
+		if entry.Proxy.SourceUpstream != "upstream-a" {
+			continue
+		}
+		reservation, ok := entry.Runtime.Reserve()
+		if !ok {
+			t.Fatal("Reserve(upstream-a) = false, want true")
+		}
+		if err := reservation.Commit(); err != nil {
+			t.Fatalf("Commit(upstream-a): %v", err)
+		}
+		held = reservation
+		break
+	}
+	if held == nil {
+		t.Fatal("upstream-a reservation was not created")
+	}
+	defer func() {
+		if err := held.Release(); err != nil {
+			t.Errorf("Release(upstream-a): %v", err)
+		}
+	}()
+
+	lease, err := New(store).Acquire(Request{
+		Now: time.Now(), RoutingName: "round-robin", Upstreams: []string{"upstream-a", "upstream-b"},
+		Strategy: routing.Strategy{Type: routing.StrategyRoundRobin},
+	})
+	if err != nil {
+		t.Fatalf("Acquire(): %v", err)
+	}
+	if lease.Proxy.SourceUpstream != "upstream-b" {
+		t.Fatalf("selected upstream = %q, want upstream-b", lease.Proxy.SourceUpstream)
+	}
+	if err := lease.Cancel(); err != nil {
+		t.Fatalf("Cancel(): %v", err)
+	}
+}
+
+func TestAcquireUsesWeightedRoutingStrategy(t *testing.T) {
+	store := routingStrategyStore(t)
+	dispatcher := New(store, &fixedRoutingRandom{values: []int{0, 2, 3}})
+	request := Request{
+		Now: time.Now(), RoutingName: "weighted", Upstreams: []string{"upstream-a", "upstream-b"},
+		Strategy: routing.Strategy{Type: routing.StrategyWeighted, Weights: map[string]uint32{"upstream-a": 3, "upstream-b": 1}},
+	}
+	for index, want := range []string{"upstream-a", "upstream-a", "upstream-b"} {
+		lease, err := dispatcher.Acquire(request)
+		if err != nil {
+			t.Fatalf("Acquire(%d): %v", index, err)
+		}
+		if lease.Proxy.SourceUpstream != want {
+			t.Fatalf("Acquire(%d) upstream = %q, want %q", index, lease.Proxy.SourceUpstream, want)
+		}
+		if err := lease.Cancel(); err != nil {
+			t.Fatalf("Cancel(%d): %v", index, err)
+		}
+	}
+}
+
+func TestAcquireUsesLeastConnectionsAndSkipsFullUpstream(t *testing.T) {
+	store := routingStrategyStore(t)
+	view := store.Current()
+	for _, entry := range view.Entries {
+		if entry.Proxy.SourceUpstream != "upstream-a" {
+			continue
+		}
+		reservation, ok := entry.Runtime.Reserve()
+		if !ok {
+			t.Fatal("Reserve(upstream-a) = false, want true")
+		}
+		if err := reservation.Commit(); err != nil {
+			t.Fatalf("Commit(upstream-a): %v", err)
+		}
+		defer func() {
+			if err := reservation.Release(); err != nil {
+				t.Errorf("Release(upstream-a): %v", err)
+			}
+		}()
+		break
+	}
+
+	lease, err := New(store).Acquire(Request{
+		Now: time.Now(), RoutingName: "least", Upstreams: []string{"upstream-a", "upstream-b"},
+		Strategy: routing.Strategy{Type: routing.StrategyLeastConnections},
+	})
+	if err != nil {
+		t.Fatalf("Acquire(): %v", err)
+	}
+	if lease.Proxy.SourceUpstream != "upstream-b" {
+		t.Fatalf("selected upstream = %q, want upstream-b", lease.Proxy.SourceUpstream)
+	}
+	if err := lease.Cancel(); err != nil {
+		t.Fatalf("Cancel(): %v", err)
+	}
+}
+
 func TestAcquireSurvivesConcurrentSnapshotApply(t *testing.T) {
 	now := time.Date(2026, 7, 28, 12, 0, 0, 0, time.UTC)
 	store := snapshot.NewStore("cluster-a", "worker-a")
@@ -246,6 +426,40 @@ func BenchmarkAcquire100kIndexed(b *testing.B) {
 	}
 }
 
+func BenchmarkAcquire100kRoutingRoundRobin(b *testing.B) {
+	store := snapshot.NewStore("cluster-a", "worker-a")
+	proxies := makeTestProxies(100_000)
+	envelope := snapshot.Envelope{
+		ClusterID: "cluster-a", WorkerID: "worker-a", Epoch: 1, Version: 1, Full: true, Proxies: proxies,
+	}
+	envelope.Checksum = snapshot.Checksum(envelope.Proxies)
+	if err := store.Apply(envelope); err != nil {
+		b.Fatalf("Apply(): %v", err)
+	}
+
+	dispatcher := New(store)
+	request := Request{
+		Now: time.Date(2026, 7, 28, 12, 0, 0, 0, time.UTC), RoutingName: "benchmark-round-robin",
+		Upstreams: []string{"upstream-a", "upstream-b"}, Strategy: routing.Strategy{Type: routing.StrategyRoundRobin},
+		Scheme: proxyDomain.SchemeHTTP, RequiredTags: map[string]string{"region": "cn-east", "tier": "gold"},
+		SafetyMargin: 5 * time.Second,
+	}
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	b.RunParallel(func(parallel *testing.PB) {
+		for parallel.Next() {
+			lease, err := dispatcher.Acquire(request)
+			if err != nil {
+				b.Fatalf("Acquire(): %v", err)
+			}
+			if err := lease.Cancel(); err != nil {
+				b.Fatalf("Cancel(): %v", err)
+			}
+		}
+	})
+}
+
 func makeTestProxies(count int) []proxyDomain.Proxy {
 	now := time.Date(2026, 7, 28, 12, 0, 0, 0, time.UTC)
 	expiresAt := now.Add(10 * time.Minute)
@@ -269,6 +483,34 @@ func makeTestProxies(count int) []proxyDomain.Proxy {
 	return proxies
 }
 
+func routingStrategyStore(t *testing.T) *snapshot.Store {
+	t.Helper()
+	store := snapshot.NewStore("cluster-a", "worker-a")
+	envelope := snapshot.Envelope{
+		ClusterID: "cluster-a", WorkerID: "worker-a", Epoch: 1, Version: 1, Full: true,
+		Proxies: []proxyDomain.Proxy{
+			{ID: "proxy-a", Scheme: proxyDomain.SchemeHTTP, SourceUpstream: "upstream-a", State: proxyDomain.StateAvailable, MaxConcurrency: 1},
+			{ID: "proxy-b", Scheme: proxyDomain.SchemeHTTP, SourceUpstream: "upstream-b", State: proxyDomain.StateAvailable, MaxConcurrency: 1},
+		},
+	}
+	envelope.Checksum = snapshot.Checksum(envelope.Proxies)
+	if err := store.Apply(envelope); err != nil {
+		t.Fatalf("Apply(): %v", err)
+	}
+	return store
+}
+
+type fixedRoutingRandom struct {
+	values []int
+	index  int
+}
+
+func (source *fixedRoutingRandom) Intn(limit int) int {
+	value := source.values[source.index]
+	source.index++
+	return value % limit
+}
+
 func schemeForIndex(index int) proxyDomain.Scheme {
 	switch index % 3 {
 	case 0:

internal/gateway/snapshot/store.go

@@ -338,6 +338,30 @@ func (v *View) MatchRouting(request routing.Request) (routing.Rule, bool) {
 	return v.routing.Match(request)
 }
 
+// UpstreamLoad returns the current in-flight load and whether an eligible
+// capacity slot remains for one Upstream under the supplied request filters.
+func (v *View) UpstreamLoad(query Query, upstream string) (int64, bool) {
+	if v == nil || upstream == "" {
+		return 0, false
+	}
+	query.Upstreams = []string{upstream}
+	selection := v.Select(query)
+	var active int64
+	available := false
+	for index := 0; index < selection.Len(); index++ {
+		entry, ok := selection.EntryAt(index)
+		if !ok {
+			continue
+		}
+		entryActive, reserved, maximum := entry.Runtime.Counters()
+		active += entryActive + reserved
+		if entryActive+reserved < maximum {
+			available = true
+		}
+	}
+	return active, available
+}
+
 func (s *Store) reclaimableRuntimes(nextProxyIDs map[string]struct{}) map[string]*runtimeRegistration {
 	result := make(map[string]*runtimeRegistration)
 	for proxyID, registration := range s.runtimes {