feat(infra): implement zero-dependency pure in-memory cache plugin

backend/plugins/infra/cache_memory/cache.go

@@ -0,0 +1,101 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package cache_memory
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+
+	"Wavelet/core"
+	"Wavelet/core/contracts"
+	"Wavelet/pkg/cache/ram"
+)
+
+type ramEntry struct {
+	data     []byte
+	expireAt time.Time
+}
+
+type memoryCacheService struct {
+	ramCache *ram.Cache[string, ramEntry]
+	events   *core.EventBus
+}
+
+func newMemoryCacheService(capacity int, events *core.EventBus) (*memoryCacheService, error) {
+	ramCache, err := ram.New[string, ramEntry](ram.Options{
+		MaximumSize: capacity,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return &memoryCacheService{
+		ramCache: ramCache,
+		events:   events,
+	}, nil
+}
+
+func (s *memoryCacheService) Get(ctx context.Context, key string, target any) error {
+	if entry, ok := s.ramCache.GetIfPresent(key); ok {
+		if entry.expireAt.IsZero() || time.Now().Before(entry.expireAt) {
+			return json.Unmarshal(entry.data, target)
+		}
+		// Expired
+		s.ramCache.Invalidate(key)
+	}
+	return contracts.ErrCacheMiss
+}
+
+func (s *memoryCacheService) Set(ctx context.Context, key string, value any, ttl time.Duration) error {
+	data, err := json.Marshal(value)
+	if err != nil {
+		return err
+	}
+
+	var expireAt time.Time
+	if ttl > 0 {
+		expireAt = time.Now().Add(ttl)
+	}
+
+	s.ramCache.Set(key, ramEntry{
+		data:     data,
+		expireAt: expireAt,
+	})
+	return nil
+}
+
+func (s *memoryCacheService) Delete(ctx context.Context, key string) error {
+	s.ramCache.Invalidate(key)
+	if s.events != nil {
+		_ = s.events.Emit(ctx, "cache:invalidate", key)
+	}
+	return nil
+}
+
+func (s *memoryCacheService) Invalidate(ctx context.Context, key string) error {
+	return s.Delete(ctx, key)
+}
+
+func (s *memoryCacheService) GetOrSet(ctx context.Context, key string, target any, ttl time.Duration, loader func() (any, error)) error {
+	err := s.Get(ctx, key, target)
+	if err == nil {
+		return nil
+	}
+
+	val, err := loader()
+	if err != nil {
+		return err
+	}
+
+	if setErr := s.Set(ctx, key, val, ttl); setErr != nil {
+		return setErr
+	}
+
+	data, err := json.Marshal(val)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(data, target)
+}