@@ -0,0 +1,185 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * Test scaffolding [#23184]: one booted sqlite `ObjectQL` engine per test file,
+ * emptied before each case that takes it, instead of one boot per case.
+ *
+ * A suite in this package that builds a real engine over better-sqlite3
+ * `:memory:` pays `init()` plus `syncSchemas()` (the DDL for every object it
+ * registers) once per case: about 80 ms for the 32 objects a SCIM deployment
+ * registers, and 6 to 10 ms for a small fixture set, so a file of 110 cases
+ * spends most of a second booting. The engine a case receives from this pool
+ * was built by the same `boot` function, so its registry, its hooks and its
+ * driver are the ones a fresh boot gives; what the previous case left behind
+ * is its ROWS, and those are deleted before the engine is handed out again.
+ *
+ * What is NOT reset, and why that is safe or refused:
+ *
+ *  - the engine's in-memory autonumber counters: a pool whose objects declare
+ *    an `autonumber` field is refused when it first boots, since a counter
+ *    seeded by an earlier case would not restart where a fresh engine does;
+ *  - the engine's memo of the install's organizations, which only an engine
+ *    write to `sys_organization` invalidates: the rows are deleted below the
+ *    engine, so a database that holds an organization row is refused rather
+ *    than emptied;
+ *  - the schema itself: a case that created or dropped a table leaves an
+ *    engine a fresh boot would not give, and the next `take()` refuses it;
+ *  - the write epoch and the log-once sets: counters and logging only, read by
+ *    nothing these suites assert on.
+ *
+ * A case may hold several engines at once: `take()` hands out a pooled engine
+ * no case holds, or boots another. Engines that were taken come back with
+ * `release()` in the file's `afterEach`, and `destroy()` closes them all in
+ * its `afterAll`. A suite that needs a differently-built engine (other hooks,
+ * other objects) boots it itself, as before; only the one `boot` shape is
+ * pooled.
+ *
+ * ```ts
+ * const pool = sqliteEnginePool(async () => ({ engine, driver }));
+ * afterEach(pool.release);
+ * afterAll(pool.destroy);
+ * const engine = await pool.take();
+ * ```
+ */
+
+import type { ObjectQL } from '@objectstack/objectql';
+import type { SqlDriver } from '@objectstack/driver-sql';
+
+/** What the pool's `boot` returns: the engine, and the driver it registered as the default. */
+export interface BootedSqliteEngine<E extends ObjectQL = ObjectQL> {
+  engine: E;
+  driver: SqlDriver;
+}
+
+export interface SqliteEnginePoolOptions<E extends ObjectQL> {
+  /** Per-engine fixture state the suite keeps beside the database (a catalog set, say), reset with it. */
+  onReset?: (engine: E) => void | Promise<void>;
+}
+
+export interface SqliteEnginePool<E extends ObjectQL> {
+  /** An emptied pooled engine no case holds, or a fresh boot when every pooled engine is held. */
+  take(): Promise<E>;
+  /** Hand back every engine taken since the last release; the file's `afterEach`. */
+  release(): void;
+  /** Destroy every engine the pool booted; the file's `afterAll`. */
+  destroy(): Promise<void>;
+  /** Boots run, and resets performed, since the pool was made. */
+  counts(): { boots: number; resets: number };
+}
+
+interface Entry<E extends ObjectQL> {
+  engine: E;
+  driver: SqlDriver;
+  /** The tables the boot created, sorted. */
+  tables: readonly string[];
+  held: boolean;
+}
+
+/** The engine's in-memory organization memo is keyed on this object's rows (see the header). */
+const ORGANIZATION_TABLE = 'sys_organization';
+
+type Knex = ReturnType<SqlDriver['getKnex']>;
+
+async function tableNames(knex: Knex): Promise<string[]> {
+  const rows = (await knex('sqlite_master').where({ type: 'table' }).select('name')) as Array<{ name: string }>;
+  return rows
+    .map((row) => row.name)
+    .filter((name) => !name.startsWith('sqlite_'))
+    .sort();
+}
+
+function autonumberFields(engine: ObjectQL): string[] {
+  const objects = engine.registry.getAllObjects() as Array<{ name: string; fields?: Record<string, { type?: string }> }>;
+  return objects.flatMap((object) =>
+    Object.entries(object.fields ?? {})
+      .filter(([, field]) => field?.type === 'autonumber')
+      .map(([name]) => `${object.name}.${name}`),
+  );
+}
+
+/** Make a pool over `boot`; see the module header for what a reused engine does and does not carry. */
+export function sqliteEnginePool<E extends ObjectQL>(
+  boot: () => Promise<BootedSqliteEngine<E>>,
+  options: SqliteEnginePoolOptions<E> = {},
+): SqliteEnginePool<E> {
+  const entries: Array<Entry<E>> = [];
+  let boots = 0;
+  let resets = 0;
+
+  async function bootEntry(): Promise<Entry<E>> {
+    const { engine, driver } = await boot();
+    boots += 1;
+    const counted = autonumberFields(engine);
+    if (counted.length > 0) {
+      try {
+        await engine.destroy();
+      } catch {
+        /* noop */
+      }
+      throw new Error(
+        `sqliteEnginePool: ${counted.join(', ')} declare an autonumber field, whose counter the engine keeps in ` +
+          'memory across a reset; boot that engine per case instead of pooling it.',
+      );
+    }
+    const entry: Entry<E> = { engine, driver, tables: await tableNames(driver.getKnex()), held: true };
+    entries.push(entry);
+    return entry;
+  }
+
+  async function empty(entry: Entry<E>): Promise<void> {
+    const knex = entry.driver.getKnex();
+    const tables = await tableNames(knex);
+    if (tables.join('\n') !== entry.tables.join('\n')) {
+      const added = tables.filter((t) => !entry.tables.includes(t));
+      const dropped = entry.tables.filter((t) => !tables.includes(t));
+      throw new Error(
+        `sqliteEnginePool: a case changed this engine's schema (created: ${added.join(', ') || 'none'}; ` +
+          `dropped: ${dropped.join(', ') || 'none'}), so it is no longer the engine a fresh boot gives. ` +
+          'Boot that case its own engine.',
+      );
+    }
+    if (tables.includes(ORGANIZATION_TABLE)) {
+      const [row] = (await knex(ORGANIZATION_TABLE).count({ n: '*' })) as Array<{ n: number | string }>;
+      if (Number(row?.n ?? 0) > 0) {
+        throw new Error(
+          `sqliteEnginePool: a case left ${row?.n} ${ORGANIZATION_TABLE} row(s), and the engine memoizes the ` +
+            'organization set until an engine write to that object invalidates it; deleting them below the ' +
+            'engine would hand the next case a stale memo. Boot that case its own engine.',
+        );
+      }
+    }
+    await knex.transaction(async (trx) => {
+      // Checked at commit, when every table is empty: the delete order does not matter.
+      await trx.raw('PRAGMA defer_foreign_keys = ON');
+      for (const table of tables) await trx(table).del();
+      const [sequence] = (await trx('sqlite_master').where({ type: 'table', name: 'sqlite_sequence' })) as unknown[];
+      if (sequence) await trx('sqlite_sequence').del();
+    });
+    await options.onReset?.(entry.engine);
+    resets += 1;
+  }
+
+  return {
+    async take() {
+      const free = entries.find((entry) => !entry.held);
+      if (!free) return (await bootEntry()).engine;
+      free.held = true;
+      await empty(free);
+      return free.engine;
+    },
+    release() {
+      for (const entry of entries) entry.held = false;
+    },
+    async destroy() {
+      while (entries.length) {
+        const entry = entries.pop()!;
+        try {
+          await entry.engine.destroy();
+        } catch {
+          /* noop */
+        }
+      }
+    },
+    counts: () => ({ boots, resets }),
+  };
+}
@@ -51,7 +51,7 @@
  * file re-run it on the same fixtures rather than describing it.
  */
 
-import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { describe, it, expect, beforeEach, afterEach, afterAll } from 'vitest';
 import { ObjectQL } from '@objectstack/objectql';
 import { SqlDriver } from '@objectstack/driver-sql';
 import { isAPIError } from 'better-auth/api';
@@ -63,6 +63,7 @@ import { SYS_USER_PROFILE_EDIT_FIELDS } from './sys-user-writable-fields.js';
 import { createObjectQLAdapterFactory } from './objectql-adapter.js';
 import { buildAdminPluginSchema, buildOrganizationPluginSchema } from './auth-schema-config.js';
 import { bindTestSecurityCatalog } from './__tests__/security-catalog.testkit.js';
+import { sqliteEnginePool, type BootedSqliteEngine } from './__tests__/sqlite-engine-pool.testkit.js';
 import { admin } from 'better-auth/plugins/admin';
 import { organization } from 'better-auth/plugins/organization';
 
@@ -246,6 +247,7 @@ afterEach(async () => {
   else process.env[POSTURE_ENV] = ambientPosture;
   if (ambientMultiOrg === undefined) delete process.env[MULTI_ORG_ENV];
   else process.env[MULTI_ORG_ENV] = ambientMultiOrg;
+  defaultEngines.release();
   // `:memory:` dies with its connection; closing keeps one live database per
   // test from piling up in a file this size.
   const open = engines;
@@ -255,17 +257,34 @@ afterEach(async () => {
   }
 });
 
+/**
+ * [#23184] Every `boot()` with no options — the engine most cases take, often
+ * twice in one case — comes from a per-file pool instead of a fresh boot: the
+ * same six objects, the same guard registration, its rows deleted and its
+ * catalog emptied before a case receives it (`sqlite-engine-pool.testkit.ts`
+ * says what a reused engine does and does not carry). 110 cases spent about a
+ * second booting engines they never told apart. Any other option set boots a
+ * fresh engine per call, as before, because its hooks differ.
+ */
+const defaultEngines = sqliteEnginePool(() => bootEngine({}), {
+  onReset: (engine) => catalogOf(engine).clear(),
+});
+afterAll(defaultEngines.destroy);
+
 async function boot(opts: BootOptions = {}): Promise<ObjectQL> {
+  if (Object.keys(opts).length === 0) return defaultEngines.take();
+  return (await bootEngine(opts, engines)).engine;
+}
+
+async function bootEngine(opts: BootOptions, track?: ObjectQL[]): Promise<BootedSqliteEngine> {
   const engine = new ObjectQL();
-  engines.push(engine);
-  engine.registerDriver(
-    new SqlDriver({
-      client: 'better-sqlite3',
-      connection: { filename: ':memory:' },
-      useNullAsDefault: true,
-    }),
-    true,
-  );
+  track?.push(engine);
+  const driver = new SqlDriver({
+    client: 'better-sqlite3',
+    connection: { filename: ':memory:' },
+    useNullAsDefault: true,
+  });
+  engine.registerDriver(driver, true);
   await engine.init();
   for (const o of [sysUser, sysMember, sysPermissionSet, sysUserPermissionSet, sysAccount, sysMetadataActivation]) {
     engine.registry.registerObject(o as never);
@@ -288,7 +307,7 @@ async function boot(opts: BootOptions = {}): Promise<ObjectQL> {
       ...(opts.maxScan !== undefined ? { maxScan: opts.maxScan } : {}),
     });
   }
-  return engine;
+  return { engine, driver };
 }
 
 /** A user row, plus whatever standing the case needs. */