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_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()
+}