feat(cache,worker): overhaul cache layer and add generation task lease recovery

- shared/cache: add Options/L1/async/metrics/prefix decorators, multi-key ops, Redis pool tuning, and JSON readthrough metrics
- worker-generate: claim tasks via DB lease + heartbeat, requeue stale queued tasks, expire dead leases with refund/cache invalidation
- tenant: version article cache keys so worker recovery invalidations propagate cleanly
- shared/config: expand Redis (pool/timeouts/TLS) and Generation (lease/recovery) configs with defaults

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/shared/cache/l1.go

@@ -0,0 +1,117 @@
+package cache
+
+import (
+	"context"
+	"strings"
+	"time"
+)
+
+type l1Cache struct {
+	inner Cache
+	local Cache
+	ttl   time.Duration
+}
+
+func newL1Cache(inner Cache, ttl time.Duration) Cache {
+	if ttl <= 0 {
+		return inner
+	}
+	return &l1Cache{inner: inner, local: newMemoryCache(), ttl: ttl}
+}
+
+func (c *l1Cache) Get(ctx context.Context, key string) ([]byte, error) {
+	if isCacheControlKey(key) {
+		return c.inner.Get(ctx, key)
+	}
+	if value, err := c.local.Get(ctx, key); err == nil {
+		recordCacheL1("hit")
+		return value, nil
+	}
+	recordCacheL1("miss")
+
+	value, err := c.inner.Get(ctx, key)
+	if err != nil {
+		return nil, err
+	}
+	_ = c.local.Set(ctx, key, value, c.ttl)
+	return value, nil
+}
+
+func (c *l1Cache) GetMulti(ctx context.Context, keys []string) (map[string][]byte, error) {
+	if len(keys) == 0 {
+		return map[string][]byte{}, nil
+	}
+
+	result := make(map[string][]byte, len(keys))
+	miss := make([]string, 0, len(keys))
+	for _, key := range keys {
+		value, err := c.local.Get(ctx, key)
+		if err == nil {
+			recordCacheL1("hit")
+			result[key] = value
+			continue
+		}
+		recordCacheL1("miss")
+		miss = append(miss, key)
+	}
+	if len(miss) == 0 {
+		return result, nil
+	}
+
+	values, err := c.inner.GetMulti(ctx, miss)
+	if err != nil {
+		return nil, err
+	}
+	for key, value := range values {
+		result[key] = value
+		_ = c.local.Set(ctx, key, value, c.ttl)
+	}
+	return result, nil
+}
+
+func (c *l1Cache) Set(ctx context.Context, key string, value []byte, ttl time.Duration) error {
+	if isCacheControlKey(key) {
+		return c.inner.Set(ctx, key, value, ttl)
+	}
+	if err := c.inner.Set(ctx, key, value, ttl); err != nil {
+		return err
+	}
+	return c.local.Set(ctx, key, value, c.l1TTL(ttl))
+}
+
+func (c *l1Cache) SetMulti(ctx context.Context, items []Item) error {
+	if err := c.inner.SetMulti(ctx, items); err != nil {
+		return err
+	}
+	for _, item := range items {
+		_ = c.local.Set(ctx, item.Key, item.Value, c.l1TTL(item.TTL))
+	}
+	return nil
+}
+
+func (c *l1Cache) Delete(ctx context.Context, key string) error {
+	_ = c.local.Delete(ctx, key)
+	return c.inner.Delete(ctx, key)
+}
+
+func (c *l1Cache) DeleteMany(ctx context.Context, keys []string) error {
+	_ = c.local.DeleteMany(ctx, keys)
+	return c.inner.DeleteMany(ctx, keys)
+}
+
+func (c *l1Cache) DeletePrefix(ctx context.Context, prefix string) error {
+	_ = c.local.DeletePrefix(ctx, prefix)
+	return c.inner.DeletePrefix(ctx, prefix)
+}
+
+func (c *l1Cache) l1TTL(ttl time.Duration) time.Duration {
+	if ttl > 0 && ttl < c.ttl {
+		return ttl
+	}
+	return c.ttl
+}
+
+func isCacheControlKey(key string) bool {
+	key = strings.TrimSpace(key)
+	return strings.HasPrefix(key, "cache:version:") || strings.Contains(key, ":cache:version:")
+}