chore: baseline snapshot before moderation-strictness feature

Repo .git was damaged (refs/ missing, index truncated, object store near-empty).
Repaired via git init (rebuilt refs), stale index preserved as .git/index.corrupt-20260910.bak,
then full worktree committed as a rollback baseline.

internal/cache/cache.go

@@ -0,0 +1,87 @@
+// Copyright 2026 tamakyi. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+// Package cache 提供进程内、并发安全的短 TTL 缓存。
+//
+// 适用场景：结果聚合统计等"非强一致"数据，用短 TTL 换取数据库实时重算压力的显著降低
+// （投票结果页、探索页热门投票等）。需注意：进程内存缓存在多实例横向扩容时不会共享，
+// 因此仅用于可接受短暂陈旧的数据；强一致数据请勿使用本缓存。
+package cache
+
+import (
+	"sync"
+	"time"
+)
+
+type ttlEntry struct {
+	value     interface{}
+	expiresAt time.Time
+}
+
+// TTLCache 并发安全的带 TTL 进程内缓存。
+type TTLCache struct {
+	mu       sync.RWMutex
+	items    map[string]ttlEntry
+	maxItems int
+}
+
+// NewTTLCache 创建缓存实例。maxItems<=0 时使用默认容量 256；达到容量上限时，
+// 先淘汰过期项，若仍满则整表清空（避免内存无限增长，短 TTL 下过期项通常已占多数）。
+func NewTTLCache(maxItems int) *TTLCache {
+	if maxItems <= 0 {
+		maxItems = 256
+	}
+	return &TTLCache{
+		items:    make(map[string]ttlEntry, maxItems),
+		maxItems: maxItems,
+	}
+}
+
+// Get 读取缓存；命中且未过期返回值，否则返回 (nil, false)。
+func (c *TTLCache) Get(key string) (interface{}, bool) {
+	c.mu.RLock()
+	e, ok := c.items[key]
+	c.mu.RUnlock()
+	if !ok {
+		return nil, false
+	}
+	if time.Now().After(e.expiresAt) {
+		c.mu.Lock()
+		// 双重检查，避免并发重复删除（无影响，仅兜底）
+		if cur, still := c.items[key]; still && time.Now().After(cur.expiresAt) {
+			delete(c.items, key)
+		}
+		c.mu.Unlock()
+		return nil, false
+	}
+	return e.value, true
+}
+
+// Set 写入缓存并设定过期时间。
+func (c *TTLCache) Set(key string, value interface{}, ttl time.Duration) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if len(c.items) >= c.maxItems {
+		// 先淘汰过期项
+		now := time.Now()
+		for k, v := range c.items {
+			if now.After(v.expiresAt) {
+				delete(c.items, k)
+			}
+		}
+		// 仍满（多为短 TTL 下瞬时高频写入）：整表重建，保证写入成功且不 OOM
+		if len(c.items) >= c.maxItems {
+			c.items = make(map[string]ttlEntry, c.maxItems)
+		}
+	}
+	c.items[key] = ttlEntry{value: value, expiresAt: time.Now().Add(ttl)}
+}
+
+// Delete 删除指定键的缓存项；键不存在时静默返回。
+// 用于写穿式失效：数据变更（如新增投票提交）后立即清除对应缓存，避免结果页短暂陈旧。
+func (c *TTLCache) Delete(key string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	delete(c.items, key)
+}

internal/cache/cache_test.go

@@ -0,0 +1,61 @@
+// Copyright 2026 tamakyi. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package cache
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestTTLCacheBasic(t *testing.T) {
+	c := NewTTLCache(8)
+	if _, ok := c.Get("missing"); ok {
+		t.Fatal("expected miss for empty cache")
+	}
+	c.Set("k", "v", time.Minute)
+	v, ok := c.Get("k")
+	if !ok || v.(string) != "v" {
+		t.Fatalf("expected hit with v, got %v %v", v, ok)
+	}
+}
+
+func TestTTLCacheExpiry(t *testing.T) {
+	c := NewTTLCache(8)
+	c.Set("k", "v", time.Nanosecond)
+	time.Sleep(2 * time.Millisecond)
+	if _, ok := c.Get("k"); ok {
+		t.Fatal("expected expired entry to miss")
+	}
+}
+
+func TestTTLCacheCapacityEviction(t *testing.T) {
+	c := NewTTLCache(4)
+	for i := 0; i < 100; i++ {
+		c.Set(string(rune('a'+i%26))+string(rune('0'+i%10)), i, time.Minute)
+	}
+	// 不 panic 且仍可读
+	if _, ok := c.Get("a0"); ok {
+		// 命中与否均可，关键是内存不失控且无 panic
+		_ = ok
+	}
+}
+
+func TestTTLCacheConcurrent(t *testing.T) {
+	c := NewTTLCache(16)
+	var wg sync.WaitGroup
+	for g := 0; g < 20; g++ {
+		wg.Add(1)
+		go func(n int) {
+			defer wg.Done()
+			for i := 0; i < 200; i++ {
+				key := string(rune('a' + (n+i)%26))
+				c.Set(key, n, time.Minute)
+				c.Get(key)
+			}
+		}(g)
+	}
+	wg.Wait()
+}