feat(worker): 实现集群限流与自适应负载

保留平台模型 RPM、TPM 和并发策略语义，增加 PostgreSQL 集群级租约、饱和候选重选和多平台自动负载，避免突发任务固定等待首个平台。\n\n新增 Worker 实时负载采样、自适应 active/heavy 容量、心跳与管理端指标，并扩展本地 acceptance runner，覆盖三 Worker、同模型三平台 2/4/6 并发和 48 个带图视频突发任务。\n\n验证：go test ./...、go vet ./...、PostgreSQL 跨 Store 集成测试、gofmt、bash -n、ShellCheck 及本地集群 provider-burst 验收通过；48/48 成功，无越限、重复提交、重复计费、重复回调或终态资源泄漏。

apps/api/internal/workerload/sampler.go

@@ -0,0 +1,131 @@
+package workerload
+
+import (
+	"errors"
+	"os"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+type SystemSampler struct {
+	mu sync.Mutex
+
+	root          string
+	lastCPUUsage  int64
+	lastCPUTime   time.Time
+	lastThrottled int64
+}
+
+func NewSystemSampler() *SystemSampler {
+	return &SystemSampler{root: "/sys/fs/cgroup"}
+}
+
+func NewSystemSamplerAt(root string) *SystemSampler {
+	return &SystemSampler{root: strings.TrimRight(root, "/")}
+}
+
+func (s *SystemSampler) Sample(databaseConnections, databaseMax int32) ResourceSample {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	now := time.Now()
+	memoryCurrent, memoryLimit := s.memory()
+	cpuUsage, throttledCount := s.cpuStat()
+	cpuLimit := s.cpuLimit()
+	cpuUtilization := 0.0
+	if s.lastCPUUsage > 0 && cpuUsage >= s.lastCPUUsage && !s.lastCPUTime.IsZero() {
+		elapsed := now.Sub(s.lastCPUTime).Seconds()
+		if elapsed > 0 {
+			cpuUtilization = float64(cpuUsage-s.lastCPUUsage) / 1_000_000 / elapsed / cpuLimit
+		}
+	}
+	throttled := s.lastThrottled > 0 && throttledCount > s.lastThrottled
+	s.lastCPUUsage = cpuUsage
+	s.lastThrottled = throttledCount
+	s.lastCPUTime = now
+	return ResourceSample{
+		MemoryCurrentBytes: memoryCurrent,
+		MemoryLimitBytes:   memoryLimit,
+		CPUUtilization:     bounded(cpuUtilization),
+		CPUThrottled:       throttled,
+		DBConnections:      databaseConnections,
+		DBMaxConnections:   databaseMax,
+		SampledAt:          now,
+	}
+}
+
+func (s *SystemSampler) memory() (int64, int64) {
+	current, currentErr := readIntFile(s.root + "/memory.current")
+	limit, limitErr := readLimitFile(s.root + "/memory.max")
+	if currentErr == nil && limitErr == nil {
+		return current, limit
+	}
+	current, _ = readIntFile(s.root + "/memory/memory.usage_in_bytes")
+	limit, _ = readLimitFile(s.root + "/memory/memory.limit_in_bytes")
+	return current, limit
+}
+
+func (s *SystemSampler) cpuStat() (usageUsec, throttled int64) {
+	data, err := os.ReadFile(s.root + "/cpu.stat")
+	if err != nil {
+		return 0, 0
+	}
+	for _, line := range strings.Split(string(data), "\n") {
+		fields := strings.Fields(line)
+		if len(fields) != 2 {
+			continue
+		}
+		value, parseErr := strconv.ParseInt(fields[1], 10, 64)
+		if parseErr != nil {
+			continue
+		}
+		switch fields[0] {
+		case "usage_usec":
+			usageUsec = value
+		case "nr_throttled":
+			throttled = value
+		}
+	}
+	return usageUsec, throttled
+}
+
+func (s *SystemSampler) cpuLimit() float64 {
+	data, err := os.ReadFile(s.root + "/cpu.max")
+	if err == nil {
+		fields := strings.Fields(string(data))
+		if len(fields) == 2 && fields[0] != "max" {
+			quota, quotaErr := strconv.ParseFloat(fields[0], 64)
+			period, periodErr := strconv.ParseFloat(fields[1], 64)
+			if quotaErr == nil && periodErr == nil && quota > 0 && period > 0 {
+				return max(quota/period, .001)
+			}
+		}
+	}
+	return max(float64(runtime.GOMAXPROCS(0)), 1)
+}
+
+func readIntFile(path string) (int64, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.ParseInt(strings.TrimSpace(string(data)), 10, 64)
+}
+
+func readLimitFile(path string) (int64, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	value := strings.TrimSpace(string(data))
+	if value == "" || value == "max" {
+		return 0, errors.New("cgroup limit is unlimited")
+	}
+	limit, err := strconv.ParseInt(value, 10, 64)
+	if err != nil || limit <= 0 || limit > 1<<60 {
+		return 0, errors.New("cgroup limit is not finite")
+	}
+	return limit, nil
+}