diff --git a/.env.example b/.env.example
index 0244045..fb7ed35 100644
--- a/.env.example
+++ b/.env.example
@@ -29,6 +29,10 @@ OT_PROXY_UPSTREAM_BASE_URL=https://api.openai.com
 OT_PROXY_DEFAULT_MODEL=gpt-4o-mini
 OT_PROXY_TIMEOUT=120s
 
+# 渠道健康检查
+OT_PROXY_HEALTH_INTERVAL=60s
+OT_PROXY_HEALTH_FAIL_THRESHOLD=2
+
 # 初始管理员（仅首次创建生效）
 OT_ADMIN_USERNAME=admin
 OT_ADMIN_EMAIL=admin@localhost
diff --git a/PLANNING.md b/PLANNING.md
index db3e057..5854a1a 100644
--- a/PLANNING.md
+++ b/PLANNING.md
@@ -471,9 +471,12 @@ pending(待审核) ──approve──▶ credited(已入账)
 - mock 上游新增 Anthropic Messages 端点，端到端验证 8 种组合（三协议 × 直通/转换 × 流式/非流式）。
 **验收**：chat 调 Claude、messages 调 OpenAI、responses 调 Claude 均正确，流式逐事件转换，usage 记账准确。
 
-### M5 渠道体系完善（◻ 规划）
-健康检查、负载均衡、重试/故障转移、并发控制、模型自动导入。
-**验收**：杀一个渠道自动切换；连续失败进 cooldown 并恢复。
+### M5 渠道体系完善（✅ 已完成）
+- `channel.Candidates` 按模型绑定取候选 + `Pick` 加权随机负载均衡；`TryAcquire` 每渠道并发信号量（满载溢出到其他渠道）。
+- `HealthMonitor` 后台定时探测，连续失败进 cooldown、恢复放回（`OT_PROXY_HEALTH_INTERVAL`/`OT_PROXY_HEALTH_FAIL_THRESHOLD`）。
+- `doProxy` 遍历候选渠道故障转移：网络错误/429/5xx/超时且未写出响应头时安全重试；流式已写出首字节放弃。
+- 单测覆盖候选过滤/加权/并发/健康状态机。
+**验收**：杀一个渠道自动切换；连续失败进 cooldown 并恢复；并发请求溢出不失败。
 
 ### M6 充值 + 审核（◻ 待定，接口/模型已预留）
 充值订单、人工审核、流水留痕、前端页面。
diff --git a/README.md b/README.md
index bffabbc..19df7e0 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 自托管的 LLM API 中转网关，功能对标 OpenRouter / one-api：统一 OpenAI 与 Anthropic 协议入口，背后对接多个上游渠道，内置用户体系、API Key 管理与用量计费。
 
-> 规划文档见 [PLANNING.md](./PLANNING.md)。当前进度：**M0-M2 + M4 已完成**（基建 + 用户/密钥/核心代理 + 前端 MVP + 管理后台基础 + 三协议互转）。
+> 规划文档见 [PLANNING.md](./PLANNING.md)。当前进度：**M0-M2 + M4-M5 已完成**（基建 + 用户/密钥/核心代理 + 前端 MVP + 管理后台基础 + 三协议互转 + 渠道体系）。
 
 ## 功能（当前）
 
@@ -13,6 +13,7 @@
   - `GET /v1/models` — 可用模型列表
   - **三协议互转**：客户端协议 × 渠道协议不匹配时自动转换（如 Chat 调用 Claude、Messages 调用 OpenAI、Responses 调用 Claude），流式逐事件转换；协议匹配时直通
   - 错误按客户端协议返回（OpenAI 格式 / Anthropic 格式）
+- **渠道体系**：按模型绑定选渠道 + 加权负载均衡；每渠道并发信号量（满载溢出）；后台健康检查（连续失败进 cooldown、恢复放回）；可安全重试的失败自动故障转移（网络错误/429/5xx/超时且未写出响应头）
 - **用户体系**：注册（开放/邀请码可切换，管理后台可改）、登录（JWT access + HttpOnly refresh cookie）、argon2id 密码
 - **API Key**：`sk-` 48 位 base62，仅存 SHA-256 哈希，明文一次性展示；支持限额/过期/白名单字段
 - **用量计费**：请求级 `usage_logs` 异步批量落库，按模型价格扣减余额，日粒度预聚合（`usage_daily`）
@@ -23,7 +24,7 @@
   - 管理后台：运营总览、渠道管理、模型与定价、用户管理、系统配置
 - **后端**：Go + Gin + GORM，SQLite（开发）/ PostgreSQL（生产）
 
-> 渠道健康检查/负载均衡/重试在 M5（见 PLANNING.md §10）。
+> 剩余：M6 充值（待定）与 M3 收尾（限流、骨架屏）。
 
 ## 快速开始（开发）
 
diff --git a/server/internal/app/app.go b/server/internal/app/app.go
index edf5033..167a434 100644
--- a/server/internal/app/app.go
+++ b/server/internal/app/app.go
@@ -6,6 +6,7 @@ import (
 	"log"
 	"time"
 
+	"github.com/openteam/server/internal/channel"
 	"github.com/openteam/server/internal/config"
 	"github.com/openteam/server/internal/pkg/crypto"
 	"github.com/openteam/server/internal/pkg/jwt"
@@ -21,7 +22,10 @@ type App struct {
 	Enc       *crypto.Encryptor
 	JWT       *jwt.Manager
 	Usage     *usage.Recorder
+	Health    *channel.HealthMonitor
 	startedAt time.Time
+	ctx       context.Context
+	cancel    context.CancelFunc
 }
 
 func New(cfg *config.Config) (*App, error) {
@@ -38,11 +42,18 @@ func New(cfg *config.Config) (*App, error) {
 		JWT:       jwt.NewManager(cfg.JWT.Secret, cfg.JWT.Issuer, cfg.JWT.AccessTTL, cfg.JWT.RefreshTTL),
 		startedAt: time.Now(),
 	}
+	a.ctx, a.cancel = context.WithCancel(context.Background())
 	a.Usage = usage.NewRecorder(db)
 
 	if err := a.Seed(); err != nil {
 		return nil, err
 	}
+
+	a.Health = channel.NewHealthMonitor(db, a.Enc, channel.HealthConfig{
+		Interval:      cfg.Proxy.HealthInterval,
+		FailThreshold: cfg.Proxy.HealthFailThreshold,
+	})
+	a.Health.Start(a.ctx)
 	return a, nil
 }
 
@@ -116,6 +127,7 @@ func (a *App) Seed() error {
 }
 
 func (a *App) Shutdown(ctx context.Context) {
+	a.cancel()
 	a.Usage.Close()
 	if sqlDB, err := a.DB.DB(); err == nil {
 		_ = sqlDB.Close()
diff --git a/server/internal/channel/channel.go b/server/internal/channel/channel.go
index bc19e3b..2369126 100644
--- a/server/internal/channel/channel.go
+++ b/server/internal/channel/channel.go
@@ -1,10 +1,12 @@
-// Package channel 渠道仓储：选择、密钥加解密、模型解析。
-// M1 实现最小选择逻辑（优先级+权重取第一个健康启用的渠道）；
-// 负载均衡/健康检查/故障转移在 M5 完善。
+// Package channel 渠道仓储：候选选择、加权负载均衡、并发控制、密钥加解密。
+// M5 起支持多候选（负载均衡 + 故障转移）与每渠道并发信号量。
 package channel
 
 import (
+	"crypto/rand"
 	"errors"
+	"math/big"
+	"sync"
 
 	"github.com/openteam/server/internal/pkg/crypto"
 	"github.com/openteam/server/internal/store"
@@ -16,47 +18,120 @@ var ErrNoChannel = errors.New("no available channel")
 type Service struct {
 	db  *gorm.DB
 	enc *crypto.Encryptor
+
+	mu   sync.Mutex
+	sems map[uint64]chan struct{}
 }
 
 func NewService(db *gorm.DB, enc *crypto.Encryptor) *Service {
-	return &Service{db: db, enc: enc}
+	return &Service{db: db, enc: enc, sems: map[uint64]chan struct{}{}}
 }
 
-// Select 选择处理请求的渠道：启用 + 健康，按 priority 升序、weight 降序。
-func (s *Service) Select() (*store.Channel, error) {
+// Candidates 返回可用渠道候选：健康 + 启用，按优先级、权重降序、id 升序排列。
+// model 非空时优先取绑定该模型的渠道；无绑定则退回全局。
+func (s *Service) Candidates(model string) []*store.Channel {
+	if model != "" {
+		var b []store.ChannelModelBinding
+		var modelIDs []uint64
+		s.db.Model(&store.Model{}).Where("name = ? AND enabled = ?", model, true).Pluck("id", &modelIDs)
+		if len(modelIDs) > 0 {
+			s.db.Where("model_id IN ?", modelIDs).Find(&b)
+			chs := s.loadBound(b)
+			if len(chs) > 0 {
+				return chs
+			}
+		}
+	}
 	var chs []store.Channel
-	if err := s.db.Where("enabled = ? AND health_status = ?", true, store.ChannelHealthHealthy).
-		Order("priority ASC, weight DESC, id ASC").Find(&chs).Error; err != nil {
-		return nil, err
+	s.db.Where("enabled = ? AND health_status = ?", true, store.ChannelHealthHealthy).
+		Order("priority ASC, weight DESC, id ASC").Find(&chs)
+	out := make([]*store.Channel, 0, len(chs))
+	for i := range chs {
+		out = append(out, &chs[i])
 	}
-	if len(chs) == 0 {
-		return nil, ErrNoChannel
+	return out
+}
+
+// loadBound 按绑定顺序加载渠道，过滤健康/启用。
+func (s *Service) loadBound(bindings []store.ChannelModelBinding) []*store.Channel {
+	if len(bindings) == 0 {
+		return nil
+	}
+	ids := make([]uint64, 0, len(bindings))
+	seen := map[uint64]bool{}
+	for _, b := range bindings {
+		if !seen[b.ChannelID] {
+			seen[b.ChannelID] = true
+			ids = append(ids, b.ChannelID)
+		}
+	}
+	var chs []store.Channel
+	s.db.Where("id IN ? AND enabled = ? AND health_status = ?", ids, true, store.ChannelHealthHealthy).
+		Order("priority ASC, weight DESC, id ASC").Find(&chs)
+	// 保持绑定顺序
+	byID := map[uint64]*store.Channel{}
+	for i := range chs {
+		byID[chs[i].ID] = &chs[i]
+	}
+	out := make([]*store.Channel, 0, len(ids))
+	for _, id := range ids {
+		if ch, ok := byID[id]; ok {
+			out = append(out, ch)
+		}
+	}
+	return out
+}
+
+// Pick 按权重加权随机选一个候选（负载均衡）。
+func (s *Service) Pick(cands []*store.Channel) *store.Channel {
+	if len(cands) == 0 {
+		return nil
+	}
+	total := 0
+	for _, c := range cands {
+		w := c.Weight
+		if w <= 0 {
+			w = 1
+		}
+		total += w
+	}
+	n, _ := rand.Int(rand.Reader, big.NewInt(int64(total)))
+	acc := 0
+	for _, c := range cands {
+		w := c.Weight
+		if w <= 0 {
+			w = 1
+		}
+		acc += w
+		if int(n.Int64()) < acc {
+			return c
+		}
+	}
+	return cands[len(cands)-1]
+}
+
+// TryAcquire 尝试获取渠道并发槽；渠道满载返回 false（调用方可溢出到其他渠道）。
+// MaxConcurrency<=0 视为不限制。
+func (s *Service) TryAcquire(ch *store.Channel) (func(), bool) {
+	if ch.MaxConcurrency <= 0 {
+		return func() {}, true
+	}
+	s.mu.Lock()
+	sem, ok := s.sems[ch.ID]
+	if !ok {
+		sem = make(chan struct{}, ch.MaxConcurrency)
+		s.sems[ch.ID] = sem
+	}
+	s.mu.Unlock()
+	select {
+	case sem <- struct{}{}:
+		return func() { <-sem }, true
+	default:
+		return nil, false
 	}
-	return &chs[0], nil
 }
 
 // UpstreamKey 解密渠道上游密钥。
 func (s *Service) UpstreamKey(ch *store.Channel) (string, error) {
 	return s.enc.Decrypt(ch.APIKeyEnc)
 }
-
-// ResolveModel 按全局模型名找到绑定渠道；M1 简化：返回绑定该模型的第一个健康渠道。
-func (s *Service) ResolveModel(modelName string) (*store.Channel, *store.ChannelModelBinding, error) {
-	var m store.Model
-	if err := s.db.Where("name = ? AND enabled = ?", modelName, true).First(&m).Error; err != nil {
-		return nil, nil, err
-	}
-	var b store.ChannelModelBinding
-	if err := s.db.Where("model_id = ?", m.ID).
-		Order("weight DESC, id ASC").First(&b).Error; err != nil {
-		return nil, nil, err
-	}
-	var ch store.Channel
-	if err := s.db.First(&ch, b.ChannelID).Error; err != nil {
-		return nil, nil, err
-	}
-	if !ch.Enabled || ch.HealthStatus != store.ChannelHealthHealthy {
-		return nil, nil, ErrNoChannel
-	}
-	return &ch, &b, nil
-}
diff --git a/server/internal/channel/channel_test.go b/server/internal/channel/channel_test.go
new file mode 100644
index 0000000..d78d2bc
--- /dev/null
+++ b/server/internal/channel/channel_test.go
@@ -0,0 +1,131 @@
+package channel
+
+import (
+	"context"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/openteam/server/internal/pkg/crypto"
+	"github.com/openteam/server/internal/store"
+	"gorm.io/gorm"
+)
+
+func newTestDB(t *testing.T) *gorm.DB {
+	t.Helper()
+	dsn := "/tmp/channel_test_" + time.Now().Format("150405.000000000") + ".db"
+	db, err := store.Open("sqlite", dsn)
+	if err != nil {
+		t.Fatalf("open db: %v", err)
+	}
+	t.Cleanup(func() {
+		sqlDB, _ := db.DB()
+		sqlDB.Close()
+		os.Remove(dsn)
+	})
+	return db
+}
+
+func seedChannel(t *testing.T, db *gorm.DB, name string, weight, priority, maxConc int) uint64 {
+	t.Helper()
+	enc := crypto.NewEncryptor("test-master-key-1234567890")
+	key, _ := enc.Encrypt("upstream-key")
+	ch := store.Channel{
+		Name: name, Provider: store.ChannelProviderOpenAI, BaseURL: "http://localhost:9000",
+		APIKeyEnc: key, Weight: weight, Priority: priority, MaxConcurrency: maxConc,
+		HealthStatus: store.ChannelHealthHealthy, Enabled: true,
+	}
+	if err := db.Create(&ch).Error; err != nil {
+		t.Fatalf("create channel: %v", err)
+	}
+	return ch.ID
+}
+
+func TestCandidatesFiltersUnhealthy(t *testing.T) {
+	db := newTestDB(t)
+	seedChannel(t, db, "a", 1, 0, 4)
+	seedChannel(t, db, "b", 5, 1, 4)
+	// 禁用渠道不入候选
+	bad := store.Channel{Name: "bad", Provider: store.ChannelProviderOpenAI, BaseURL: "http://x", APIKeyEnc: "x", HealthStatus: store.ChannelHealthCooldown, Enabled: true}
+	db.Create(&bad)
+
+	s := NewService(db, crypto.NewEncryptor("test-master-key-1234567890"))
+	cands := s.Candidates("")
+	if len(cands) != 2 {
+		t.Fatalf("candidates = %d, want 2", len(cands))
+	}
+	if cands[0].Name != "a" {
+		t.Fatalf("first by priority should be a, got %s", cands[0].Name)
+	}
+}
+
+func TestPickWeighted(t *testing.T) {
+	db := newTestDB(t)
+	seedChannel(t, db, "only", 1, 0, 4)
+	s := NewService(db, crypto.NewEncryptor("test-master-key-1234567890"))
+	cands := s.Candidates("")
+	chosen := s.Pick(cands)
+	if chosen == nil || chosen.Name != "only" {
+		t.Fatalf("pick single: %+v", chosen)
+	}
+	// 空候选返回 nil
+	if p := s.Pick(nil); p != nil {
+		t.Fatal("expected nil for empty candidates")
+	}
+}
+
+func TestTryAcquire(t *testing.T) {
+	db := newTestDB(t)
+	id := seedChannel(t, db, "c", 1, 0, 1)
+	var ch store.Channel
+	db.First(&ch, id)
+	s := NewService(db, crypto.NewEncryptor("test-master-key-1234567890"))
+	release, ok := s.TryAcquire(&ch)
+	if !ok {
+		t.Fatal("first acquire should succeed")
+	}
+	if _, ok := s.TryAcquire(&ch); ok {
+		t.Fatal("second acquire should fail (capacity 1)")
+	}
+	release()
+	if _, ok := s.TryAcquire(&ch); !ok {
+		t.Fatal("acquire after release should succeed")
+	}
+}
+
+func TestHealthCooldownAndRecovery(t *testing.T) {
+	db := newTestDB(t)
+	id := seedChannel(t, db, "h", 1, 0, 4)
+	var ch store.Channel
+	db.First(&ch, id)
+
+	m := NewHealthMonitor(db, crypto.NewEncryptor("test-master-key-1234567890"), HealthConfig{
+		Interval: time.Minute, FailThreshold: 2, Timeout: time.Second,
+	})
+
+	// 两次失败 → cooldown
+	m.record(&ch, false)
+	if ch.HealthStatus != store.ChannelHealthHealthy {
+		t.Fatal("one failure should stay healthy")
+	}
+	m.record(&ch, false)
+	if ch.HealthStatus != store.ChannelHealthCooldown {
+		t.Fatalf("two failures should cooldown, got %s", ch.HealthStatus)
+	}
+	// 恢复
+	m.record(&ch, true)
+	if ch.HealthStatus != store.ChannelHealthHealthy {
+		t.Fatalf("success should recover, got %s", ch.HealthStatus)
+	}
+}
+
+func TestHealthStartStops(t *testing.T) {
+	db := newTestDB(t)
+	seedChannel(t, db, "probe", 1, 0, 4)
+	m := NewHealthMonitor(db, crypto.NewEncryptor("test-master-key-1234567890"), HealthConfig{
+		Interval: time.Hour, FailThreshold: 2, Timeout: time.Second,
+	})
+	ctx, cancel := context.WithCancel(context.Background())
+	m.Start(ctx)
+	cancel() // 不应 panic
+}
diff --git a/server/internal/channel/health.go b/server/internal/channel/health.go
new file mode 100644
index 0000000..9a7a45d
--- /dev/null
+++ b/server/internal/channel/health.go
@@ -0,0 +1,122 @@
+package channel
+
+import (
+	"context"
+	"log"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/openteam/server/internal/pkg/crypto"
+	"github.com/openteam/server/internal/store"
+	"gorm.io/gorm"
+)
+
+// HealthConfig 健康检查参数。
+type HealthConfig struct {
+	Interval      time.Duration // 探测周期
+	FailThreshold int           // 连续失败 N 次进入 cooldown
+	Timeout       time.Duration // 单次探测超时
+}
+
+// HealthMonitor 定时探测渠道健康状态。
+type HealthMonitor struct {
+	db   *gorm.DB
+	enc  *crypto.Encryptor
+	cfg  HealthConfig
+	hc   *http.Client
+	mu   sync.Mutex
+	fail map[uint64]int // 渠道连续失败次数
+}
+
+func NewHealthMonitor(db *gorm.DB, enc *crypto.Encryptor, cfg HealthConfig) *HealthMonitor {
+	if cfg.Interval <= 0 {
+		cfg.Interval = 60 * time.Second
+	}
+	if cfg.FailThreshold <= 0 {
+		cfg.FailThreshold = 2
+	}
+	if cfg.Timeout <= 0 {
+		cfg.Timeout = 5 * time.Second
+	}
+	return &HealthMonitor{
+		db: db, enc: enc, cfg: cfg,
+		hc:   &http.Client{Timeout: cfg.Timeout},
+		fail: map[uint64]int{},
+	}
+}
+
+// Start 启动后台探测循环（ctx 取消即停止）。
+func (h *HealthMonitor) Start(ctx context.Context) {
+	go func() {
+		ticker := time.NewTicker(h.cfg.Interval)
+		defer ticker.Stop()
+		h.probeAll()
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-ticker.C:
+				h.probeAll()
+			}
+		}
+	}()
+	log.Printf("health: monitor started (interval=%s, threshold=%d)", h.cfg.Interval, h.cfg.FailThreshold)
+}
+
+// probeAll 探测所有启用渠道并更新健康状态。
+func (h *HealthMonitor) probeAll() {
+	var chs []store.Channel
+	if err := h.db.Where("enabled = ?", true).Find(&chs).Error; err != nil {
+		return
+	}
+	for i := range chs {
+		h.probe(&chs[i])
+	}
+}
+
+// probe 单渠道探测：GET {base}/v1/models。
+func (h *HealthMonitor) probe(ch *store.Channel) {
+	key, err := h.enc.Decrypt(ch.APIKeyEnc)
+	if err != nil {
+		h.record(ch, false)
+		return
+	}
+	url := strings.TrimRight(ch.BaseURL, "/") + "/v1/models"
+	req, _ := http.NewRequest(http.MethodGet, url, nil)
+	req.Header.Set("Authorization", "Bearer "+key)
+	req.Header.Set("Accept", "application/json")
+	resp, err := h.hc.Do(req)
+	ok := err == nil && resp.StatusCode >= 200 && resp.StatusCode < 300
+	if resp != nil {
+		resp.Body.Close()
+	}
+	h.record(ch, ok)
+}
+
+// record 记录一次探测结果，按阈值切换健康状态。
+func (h *HealthMonitor) record(ch *store.Channel, ok bool) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+
+	prev := ch.HealthStatus
+	if ok {
+		h.fail[ch.ID] = 0
+		if prev != store.ChannelHealthHealthy {
+			h.setStatus(ch, store.ChannelHealthHealthy)
+			log.Printf("health: channel %q recovered -> healthy", ch.Name)
+		}
+		return
+	}
+	h.fail[ch.ID]++
+	if h.fail[ch.ID] >= h.cfg.FailThreshold && prev != store.ChannelHealthCooldown {
+		h.setStatus(ch, store.ChannelHealthCooldown)
+		log.Printf("health: channel %q -> cooldown (%d consecutive failures)", ch.Name, h.fail[ch.ID])
+	}
+}
+
+func (h *HealthMonitor) setStatus(ch *store.Channel, status string) {
+	h.db.Model(&store.Channel{}).Where("id = ?", ch.ID).Update("health_status", status)
+	ch.HealthStatus = status
+}
diff --git a/server/internal/config/config.go b/server/internal/config/config.go
index d5c2f48..a44c234 100644
--- a/server/internal/config/config.go
+++ b/server/internal/config/config.go
@@ -50,6 +50,8 @@ type ProxyConfig struct {
 	UpstreamKey        string // 渠道上游 key 默认值
 	DefaultModel       string // 渠道模型导入时使用的模型名
 	Timeout            time.Duration
+	HealthInterval     time.Duration // 渠道健康检查周期
+	HealthFailThreshold int          // 连续失败 N 次进 cooldown
 }
 
 // loadDotEnv 读取 .env 并把 KEY=VALUE 注入环境变量（AutomaticEnv 自动映射 OT_ 前缀）。
@@ -111,6 +113,8 @@ func Load() (*Config, error) {
 	v.SetDefault("proxy.upstream_key", "")
 	v.SetDefault("proxy.default_model", "gpt-4o-mini")
 	v.SetDefault("proxy.timeout", "120s")
+	v.SetDefault("proxy.health_interval", "60s")
+	v.SetDefault("proxy.health_fail_threshold", 2)
 
 	return &Config{
 		Env:  v.GetString("env"),
@@ -137,11 +141,13 @@ func Load() (*Config, error) {
 			SaltLen:          v.GetInt("auth.salt_len"),
 		},
 		Proxy: ProxyConfig{
-			DefaultChannelName: v.GetString("proxy.default_channel_name"),
-			UpstreamBaseURL:    v.GetString("proxy.upstream_base_url"),
-			UpstreamKey:        v.GetString("proxy.upstream_key"),
-			DefaultModel:       v.GetString("proxy.default_model"),
-			Timeout:            v.GetDuration("proxy.timeout"),
+			DefaultChannelName:  v.GetString("proxy.default_channel_name"),
+			UpstreamBaseURL:     v.GetString("proxy.upstream_base_url"),
+			UpstreamKey:         v.GetString("proxy.upstream_key"),
+			DefaultModel:        v.GetString("proxy.default_model"),
+			Timeout:             v.GetDuration("proxy.timeout"),
+			HealthInterval:      v.GetDuration("proxy.health_interval"),
+			HealthFailThreshold: v.GetInt("proxy.health_fail_threshold"),
 		},
 		Master: v.GetString("master_key"),
 	}, nil
diff --git a/server/internal/proxy/gateway.go b/server/internal/proxy/gateway.go
index e47017e..031e87f 100644
--- a/server/internal/proxy/gateway.go
+++ b/server/internal/proxy/gateway.go
@@ -123,14 +123,9 @@ func (g *Gateway) models(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"object": "list", "data": data})
 }
 
-// selectChannel 选渠道：优先按模型绑定解析，退化为全局选渠道。
-func (g *Gateway) selectChannel(c *gin.Context, model string) (*store.Channel, error) {
-	if model != "" {
-		if ch, _, err := g.ch.ResolveModel(model); err == nil {
-			return ch, nil
-		}
-	}
-	return g.ch.Select()
+// candidateChannels 返回可用渠道候选（按模型绑定优先，退化全局）。
+func (g *Gateway) candidateChannels(model string) []*store.Channel {
+	return g.ch.Candidates(model)
 }
 
 // resolveUser 取当前用户（含余额）。
diff --git a/server/internal/proxy/handlers.go b/server/internal/proxy/handlers.go
index f5e7e4a..50267af 100644
--- a/server/internal/proxy/handlers.go
+++ b/server/internal/proxy/handlers.go
@@ -24,20 +24,15 @@ func (g *Gateway) chatCompletions(c *gin.Context) {
 	c.Set("protocol", convert.ProtoChat)
 	c.Set("model_name", br.Model)
 
-	ch, err := g.selectChannel(c, br.Model)
-	if err != nil {
+	cands := g.candidateChannels(br.Model)
+	if len(cands) == 0 {
 		apiError(c, http.StatusServiceUnavailable, "no_channel", "No available upstream channel")
 		g.recordError(c, nil, nil, now(), "no_channel")
 		return
 	}
-	plan, err := prepareUpstream(ch.Provider, convert.ProtoChat, body)
-	if err != nil {
-		apiError(c, http.StatusInternalServerError, "conversion_error", "Failed to convert request: "+err.Error())
-		return
-	}
 	sink := &usageSink{}
 	c.Set("usage_raw", &sinkHolder{sink: sink})
-	g.doProxy(c, ch, plan, br.Stream, sink)
+	g.doProxy(c, cands, convert.ProtoChat, body, br.Stream, sink)
 }
 
 // responses POST /v1/responses（OpenAI Responses API）
@@ -57,20 +52,15 @@ func (g *Gateway) responses(c *gin.Context) {
 	c.Set("protocol", convert.ProtoResponses)
 	c.Set("model_name", br.Model)
 
-	ch, err := g.selectChannel(c, br.Model)
-	if err != nil {
+	cands := g.candidateChannels(br.Model)
+	if len(cands) == 0 {
 		apiError(c, http.StatusServiceUnavailable, "no_channel", "No available upstream channel")
 		g.recordError(c, nil, nil, now(), "no_channel")
 		return
 	}
-	plan, err := prepareUpstream(ch.Provider, convert.ProtoResponses, body)
-	if err != nil {
-		apiError(c, http.StatusInternalServerError, "conversion_error", "Failed to convert request: "+err.Error())
-		return
-	}
 	sink := &usageSink{}
 	c.Set("usage_raw", &sinkHolder{sink: sink})
-	g.doProxy(c, ch, plan, br.Stream, sink)
+	g.doProxy(c, cands, convert.ProtoResponses, body, br.Stream, sink)
 }
 
 // messages POST /v1/messages（Anthropic Messages API）
@@ -90,20 +80,15 @@ func (g *Gateway) messages(c *gin.Context) {
 	c.Set("protocol", convert.ProtoMessages)
 	c.Set("model_name", br.Model)
 
-	ch, err := g.selectChannel(c, br.Model)
-	if err != nil {
+	cands := g.candidateChannels(br.Model)
+	if len(cands) == 0 {
 		apiError(c, http.StatusServiceUnavailable, "no_channel", "No available upstream channel")
 		g.recordError(c, nil, nil, now(), "no_channel")
 		return
 	}
-	plan, err := prepareUpstream(ch.Provider, convert.ProtoMessages, body)
-	if err != nil {
-		apiError(c, http.StatusInternalServerError, "conversion_error", "Failed to convert request: "+err.Error())
-		return
-	}
 	sink := &usageSink{}
 	c.Set("usage_raw", &sinkHolder{sink: sink})
-	g.doProxy(c, ch, plan, br.Stream, sink)
+	g.doProxy(c, cands, convert.ProtoMessages, body, br.Stream, sink)
 }
 
 // usageSinkHolder 桥接：gin context 里保存 sink 引用，供 finishUsage 读取最终 usage。
diff --git a/server/internal/proxy/passthrough.go b/server/internal/proxy/passthrough.go
index 70dc36b..e440183 100644
--- a/server/internal/proxy/passthrough.go
+++ b/server/internal/proxy/passthrough.go
@@ -48,12 +48,45 @@ func upstreamURL(ch *store.Channel, path string) string {
 	return strings.TrimRight(ch.BaseURL, "/") + path
 }
 
-// doProxy 通用代理：替换 Authorization 为渠道密钥，转发请求；按 plan 决定路径与转换。
-func (g *Gateway) doProxy(c *gin.Context, ch *store.Channel, plan *upstreamPlan, stream bool, sink *usageSink) {
+// doProxy 通用代理（M5）：遍历候选渠道，按需转换；可安全重试的失败自动故障转移。
+func (g *Gateway) doProxy(c *gin.Context, cands []*store.Channel, clientProto string, body []byte, stream bool, sink *usageSink) {
+	var lastStatus = http.StatusBadGateway
+	var lastBody = []byte("all upstream channels failed")
+	for _, ch := range cands {
+		plan, err := prepareUpstream(ch.Provider, clientProto, body)
+		if err != nil {
+			lastStatus, lastBody = http.StatusInternalServerError, []byte("conversion error: "+err.Error())
+			continue
+		}
+		release, ok := g.ch.TryAcquire(ch)
+		if !ok {
+			continue // 渠道满载，溢出到下一个
+		}
+		written, retry, st, b := g.proxyOne(c, ch, plan, stream, sink)
+		release()
+		if written {
+			return
+		}
+		if !retry {
+			// 非重试性失败（如 400）：透传上游错误体
+			c.Header("Content-Type", "application/json")
+			c.Data(st, "application/json", b)
+			g.recordError(c, ch, nil, now(), "upstream_http_"+strconv.Itoa(st))
+			return
+		}
+		lastStatus, lastBody = st, b
+	}
+	// 全部候选重试性失败
+	apiError(c, lastStatus, "upstream_error", string(lastBody))
+	g.recordError(c, nil, nil, now(), "all_channels_failed")
+}
+
+// proxyOne 对单个渠道执行一次代理。
+// 返回：written=是否已写客户端响应；retry=是否可安全换渠道重试；status+respBody=失败信息。
+func (g *Gateway) proxyOne(c *gin.Context, ch *store.Channel, plan *upstreamPlan, stream bool, sink *usageSink) (written bool, retry bool, status int, respBody []byte) {
 	upKey, err := g.ch.UpstreamKey(ch)
 	if err != nil {
-		apiError(c, http.StatusInternalServerError, "channel_error", "failed to decrypt channel key")
-		return
+		return false, true, http.StatusInternalServerError, []byte("failed to decrypt channel key")
 	}
 
 	upBody := plan.body
@@ -72,8 +105,7 @@ func (g *Gateway) doProxy(c *gin.Context, ch *store.Channel, plan *upstreamPlan,
 	defer cancel()
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, upstreamURL(ch, plan.path), bytes.NewReader(upBody))
 	if err != nil {
-		apiError(c, http.StatusInternalServerError, "internal_error", "failed to build upstream request")
-		return
+		return false, false, http.StatusInternalServerError, []byte("failed to build upstream request")
 	}
 	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("Authorization", "Bearer "+upKey)
@@ -84,7 +116,6 @@ func (g *Gateway) doProxy(c *gin.Context, ch *store.Channel, plan *upstreamPlan,
 	if plan.path == "/v1/messages" {
 		req.Header.Set("anthropic-version", "2023-06-01")
 	}
-	// 透传 OpenAI 生态请求头（组织/项目等）
 	for _, h := range []string{"OpenAI-Organization", "OpenAI-Project", "OpenAI-Beta"} {
 		if v := c.GetHeader(h); v != "" {
 			req.Header.Set(h, v)
@@ -94,29 +125,20 @@ func (g *Gateway) doProxy(c *gin.Context, ch *store.Channel, plan *upstreamPlan,
 	start := time.Now()
 	resp, err := g.hc.Do(req)
 	if err != nil {
-		status := http.StatusBadGateway
-		msg := "Upstream request failed: " + err.Error()
 		if ctx.Err() == context.DeadlineExceeded {
-			status = http.StatusGatewayTimeout
-			msg = "Upstream request timed out"
+			return false, true, http.StatusGatewayTimeout, []byte("upstream request timed out")
 		}
-		apiError(c, status, "upstream_error", msg)
-		g.recordError(c, ch, nil, start, "upstream_error")
-		return
+		return false, true, http.StatusBadGateway, []byte("upstream request failed: " + err.Error())
 	}
 	defer resp.Body.Close()
 
-	// 非 2xx：透传上游错误体，并记录 error 用量
+	// 非 2xx：429/5xx 可重试；其余透传错误体
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 		errBody, _ := io.ReadAll(resp.Body)
-		status := resp.StatusCode
-		if status >= 500 {
-			status = http.StatusBadGateway
+		if resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode >= 500 {
+			return false, true, resp.StatusCode, errBody
 		}
-		c.Header("Content-Type", "application/json")
-		c.DataFromReader(status, int64(len(errBody)), "application/json", bytes.NewReader(errBody), nil)
-		g.recordError(c, ch, resp, start, "upstream_http_"+strconv.Itoa(resp.StatusCode))
-		return
+		return false, false, resp.StatusCode, errBody
 	}
 
 	c.Header("Content-Type", resp.Header.Get("Content-Type"))
@@ -126,6 +148,7 @@ func (g *Gateway) doProxy(c *gin.Context, ch *store.Channel, plan *upstreamPlan,
 	} else {
 		g.copyAndCapture(c, ch, resp.Body, start, plan.bodyConv, sink)
 	}
+	return true, false, http.StatusOK, nil
 }
 
 // copyAndCapture 非流式：整体转发（可转换）+ 解析 usage + 记账。