fix(P0): SSTable rangeScan 尾块漏读 — 索引块记录块尾 key 但二分按块首语义定位，endKey 落在块尾时下一块被排除导致二级索引查询丢数据（5万行丢106~771条）；endBlockIdx 多扫一块 + 4 个 sstable 边界回归 + 重建二级索引大数据量回归（含崩溃恢复）。附带：checkpoint 同步 flush 二级索引 LSM（P1）、kv 后端页面化 + SharedMemoryBackend chunk 化、生产负载验证测试

tests/engine/aria-idx-flush-race.test.ts

@@ -0,0 +1,123 @@
+/**
+ * v0.6.1-fix(P0) — 二级索引大数据量完整性回归测试
+ *
+ * 覆盖两类根因：
+ * 1. LSM.put 的 `!this.flushing` 条件竞态（修复：每次 freeze 一律挂链）
+ * 2. SSTable rangeScan 尾块漏读（索引键为块尾 key，locateBlockLE 排除
+ *    尾 key 越界的下一块 → 范围扫描丢尾部数据；修复：endBlockIdx 多扫一块）
+ */
+import { AriaEngine } from '../../src/engine/aria/index';
+import { createSchema } from '../../src/table/schema';
+import { installOPFSMock } from '../helpers/opfs-mock';
+
+let counter = 0;
+function uniqueDB(): string {
+  return `idxrace-${Date.now()}-${++counter}-${Math.random().toString(36).slice(2, 6)}`;
+}
+
+beforeEach(() => { installOPFSMock(new Map()); });
+
+describe('AriaEngine — 二级索引完整性（P0 回归）', () => {
+  it('5 万行写入：索引查询与主表一致（修复前丢 106~771 条）', async () => {
+    const engine = new AriaEngine({
+      storageBackend: 'opfs',
+      memtableSizeThreshold: 256 * 1024,
+      checkpointInterval: 2000,
+      walSyncMode: 'full',
+    });
+    await engine.open(uniqueDB(), 1);
+    await engine.createTable(createSchema('big', {
+      id: { type: 'string', primaryKey: true },
+      val: { type: 'number' },
+      tag: { type: 'string', index: true },
+      name: { type: 'string' },
+    }));
+
+    const TOTAL = 50000;
+    for (let batch = 0; batch < TOTAL / 1000; batch++) {
+      const rows = [] as Record<string, unknown>[];
+      for (let i = 0; i < 1000; i++) {
+        const idx = batch * 1000 + i;
+        rows.push({ id: `k${idx}`, val: idx, tag: `t${idx % 10}`, name: `User${idx}` });
+      }
+      await engine.insert('big', rows);
+    }
+
+    expect(await engine.count('big')).toBe(TOTAL);
+
+    // 每个 tag 的索引查询都完整（修复前丢 106-771 条）
+    for (let t = 0; t < 10; t++) {
+      const viaIdx = await engine.find('big', { table: 'big', where: { tag: `t${t}` } });
+      expect(viaIdx.length).toBe(5000);
+    }
+
+    // 崩溃恢复后索引仍完整
+    await (engine as any).backend.close();
+    (engine as any).opened = false;
+    const engine2 = new AriaEngine({
+      storageBackend: 'opfs',
+      memtableSizeThreshold: 256 * 1024,
+      checkpointInterval: 2000,
+      walSyncMode: 'full',
+    });
+    await engine2.open((engine as any).dbName, 1);
+    for (let t = 0; t < 10; t++) {
+      const viaIdx = await engine2.find('big', { table: 'big', where: { tag: `t${t}` } });
+      expect(viaIdx.length).toBe(5000);
+    }
+    await engine2.close();
+  }, 180000);
+
+  it('小批量高频写入（每批 50 行）触发极端 freeze 竞态', async () => {
+    const engine = new AriaEngine({
+      storageBackend: 'opfs',
+      memtableSizeThreshold: 32 * 1024,
+      checkpointInterval: 5000,
+      walSyncMode: 'full',
+    });
+    await engine.open(uniqueDB(), 1);
+    await engine.createTable(createSchema('items', {
+      id: { type: 'string', primaryKey: true },
+      tag: { type: 'string', index: true },
+    }));
+
+    const TOTAL = 4000;
+    for (let i = 0; i < TOTAL; i++) {
+      await engine.insert('items', [{ id: `k${i}`, tag: i % 3 === 0 ? 'a' : 'b' }]);
+    }
+    expect(await engine.count('items')).toBe(TOTAL);
+    expect(await engine.find('items', { table: 'items', where: { tag: 'a' } })).toHaveLength(Math.ceil(TOTAL / 3));
+    expect(await engine.find('items', { table: 'items', where: { tag: 'b' } })).toHaveLength(TOTAL - Math.ceil(TOTAL / 3));
+    await engine.close();
+  }, 120000);
+
+  it('多索引列同时写入：每列索引都完整', async () => {
+    const engine = new AriaEngine({
+      storageBackend: 'opfs',
+      memtableSizeThreshold: 64 * 1024,
+      checkpointInterval: 5000,
+      walSyncMode: 'full',
+    });
+    await engine.open(uniqueDB(), 1);
+    await engine.createTable(createSchema('multi', {
+      id: { type: 'string', primaryKey: true },
+      cat: { type: 'string', index: true },
+      grp: { type: 'number', index: true },
+    }));
+
+    const TOTAL = 6000;
+    for (let batch = 0; batch < TOTAL / 100; batch++) {
+      const rows = [] as Record<string, unknown>[];
+      for (let i = 0; i < 100; i++) {
+        const idx = batch * 100 + i;
+        rows.push({ id: `k${idx}`, cat: idx % 2 === 0 ? 'even' : 'odd', grp: idx % 5 });
+      }
+      await engine.insert('multi', rows);
+    }
+    expect(await engine.find('multi', { table: 'multi', where: { cat: 'even' } })).toHaveLength(TOTAL / 2);
+    expect(await engine.find('multi', { table: 'multi', where: { cat: 'odd' } })).toHaveLength(TOTAL / 2);
+    expect(await engine.find('multi', { table: 'multi', where: { grp: 0 } })).toHaveLength(TOTAL / 5);
+    expect(await engine.find('multi', { table: 'multi', where: { grp: 4 } })).toHaveLength(TOTAL / 5);
+    await engine.close();
+  }, 120000);
+});