优化数据库读写

tests/state-cache.test.mjs

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+import assert from 'node:assert/strict';
+import { createStateCache } from '../src/database/state-cache.mjs';
+
+let loads = 0;
+let release;
+const gate = new Promise(resolve => { release = resolve; });
+const coalesced = createStateCache({
+  maxAgeMs: 30000,
+  async load() {
+    loads += 1;
+    await gate;
+    return { load: loads };
+  }
+});
+const firstPending = coalesced.read();
+const secondPending = coalesced.read();
+release();
+const [first, second] = await Promise.all([firstPending, secondPending]);
+assert.equal(loads, 1, '并发冷读取应合并为一次全量加载');
+assert.strictEqual(first, second, '并发读取应共享同一份快照');
+assert.strictEqual(await coalesced.read(), first, '有效期内应直接复用内存快照');
+
+coalesced.invalidate();
+const afterInvalidation = await coalesced.read();
+assert.equal(loads, 2, '应用写入失效后应重新加载');
+assert.notStrictEqual(afterInvalidation, first, '失效后不得继续返回旧快照');
+
+let version = 1;
+let versionLoads = 0;
+const versioned = createStateCache({
+  version: () => version,
+  load: () => ({ load: ++versionLoads })
+});
+const versionOne = await versioned.read();
+assert.strictEqual(await versioned.read(), versionOne, '数据库版本未变化时应复用快照');
+version += 1;
+const versionTwo = await versioned.read();
+assert.equal(versionLoads, 2, '外部数据库版本变化后应重新加载');
+assert.notStrictEqual(versionTwo, versionOne, '外部写入后不得返回旧快照');
+
+console.log('State cache tests passed');