sqlite: run backup completion in callback scope

Run SQLite backup after-work callbacks inside an internal callback
scope. This drains promise reactions and next ticks before the event
loop can become idle.

Add a child-process regression test where backup is the final active
request.

Assisted-by: Codex
Signed-off-by: Filip Skokan <panva.ip@gmail.com>

Author: panva

src/node_sqlite.cc

@@ -624,9 +624,13 @@ class BackupJob : public ThreadPoolWork {
   }
 
   void AfterThreadPoolWork(int status) override {
-    HandleScope handle_scope(env()->isolate());
+    Isolate* isolate = env()->isolate();
+    HandleScope handle_scope(isolate);
+    Context::Scope context_scope(env()->context());
+    InternalCallbackScope callback_scope(
+        env(), Object::New(isolate), {0, 0}, InternalCallbackScope::kNoFlags);
     Local<Promise::Resolver> resolver =
-        Local<Promise::Resolver>::New(env()->isolate(), resolver_);
+        Local<Promise::Resolver>::New(isolate, resolver_);
 
     if (!(backup_status_ == SQLITE_OK || backup_status_ == SQLITE_DONE ||
           backup_status_ == SQLITE_BUSY || backup_status_ == SQLITE_LOCKED)) {

test/fixtures/sqlite/backup-last-request.mjs

@@ -0,0 +1,34 @@
+import { backup, DatabaseSync } from 'node:sqlite';
+
+const source = new DatabaseSync(':memory:');
+source.exec(`
+  CREATE TABLE data(value);
+  INSERT INTO data VALUES (zeroblob(1048576));
+`);
+
+let keepAlive = setInterval(() => {}, 1_000);
+let settled = false;
+
+process.once('beforeExit', () => {
+  if (!settled) {
+    process.stderr.write('backup promise did not settle before the event loop became idle\n');
+    process.exit(1);
+  }
+});
+
+backup(source, process.argv[2], {
+  rate: 1,
+  progress() {
+    if (keepAlive !== undefined) {
+      clearInterval(keepAlive);
+      keepAlive = undefined;
+    }
+  },
+}).then(() => {
+  settled = true;
+  source.close();
+}, (error) => {
+  settled = true;
+  process.stderr.write(`${error.stack ?? error}\n`);
+  process.exitCode = 1;
+});

test/parallel/test-sqlite-backup.mjs

@@ -1,5 +1,10 @@
 // Flags: --expose-gc
-import { isWindows, skipIfSQLiteMissing } from '../common/index.mjs';
+import {
+  isWindows,
+  skipIfSQLiteMissing,
+  spawnPromisified,
+} from '../common/index.mjs';
+import fixtures from '../common/fixtures.js';
 import tmpdir from '../common/tmpdir.js';
 import { join } from 'node:path';
 import { describe, test } from 'node:test';
@@ -364,3 +369,13 @@ test('source database is kept alive while a backup is in flight', async (t) => {
   const rows = backupDb.prepare('SELECT COUNT(*) AS n FROM data').get();
   t.assert.strictEqual(rows.n, 500);
 });
+
+test('backup promise settles when the backup is the last active request', async (t) => {
+  const { code, signal, stderr } = await spawnPromisified(process.execPath, [
+    fixtures.path('sqlite', 'backup-last-request.mjs'),
+    nextDb(),
+  ]);
+
+  t.assert.strictEqual(signal, null);
+  t.assert.strictEqual(code, 0, stderr);
+});