Add transaction method stubs to IndexedDB engine

[Copilot]

IndexedDB engine was missing begin, commit, and rollback methods, causing engines[...].begin is not a function errors when using transaction statements.

Changes

• src/91indexeddb.js: Added IDB.begin(), IDB.commit(), and IDB.rollback() methods (29 lines)
  • IDB.commit() - Simple no-op returning success (IndexedDB auto-commits per operation)
  • IDB.begin - Alias to commit (follows LOCALSTORAGE pattern)
  • IDB.rollback() - No-op with documentation that operations cannot be undone
• test/test2361.js: Browser test suite covering transaction statement execution

Implementation

Methods implemented as no-ops because IndexedDB manages transactions internally per operation. Each operation (insert, select, update, delete) automatically commits when complete.

This provides API compatibility so user code works without errors, while respecting IndexedDB's native auto-commit behavior.

// Now works without errors
alasql.promise(['ATTACH INDEXEDDB DATABASE mydb', 'USE mydb'])
  .then(() => alasql.promise('BEGIN TRANSACTION'))
  .then(() => alasql.promise(query))
  .then(() => alasql.promise('COMMIT TRANSACTION'))

Follows the same pattern as LOCALSTORAGE where begin is an alias to commit.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>transactions does not seem to work with indexeddb</issue_title>
<issue_description>Hello.

I'm trying to use alasql for our browser app.
We need to use transactions on IndexedDb. It seems that transactions are not implemented for INDEXEDDB.

Here's my code
`const queriesAttach = [
'ATTACH INDEXEDDB DATABASE ' + SCHEMA_NAME,
'USE ' + SCHEMA_NAME
];

return new Observable((subscriber) => {
  alasql.promise(queriesAttach)
    .then(() => alasql.promise('BEGIN TRANSACTION'))
    .then(() => alasql.promise(query))
    .then(() => alasql.promise('COMMIT TRANSACTION'))
    .then((res) => subscriber.next(res))
    .catch((error) => console.error(error));
});`

I get the error
l.engines[l.databases[l.useid].engineid].begin is not a function </issue_description>

Comments on the Issue (you are @copilot in this section)

@mathiasrw Thank you!

• Fixes transactions does not seem to work with indexeddb #1969

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[mathiasrw]

@copilot

Methods implemented as successful no-ops because IndexedDB manages transactions internally per operation

Should we forward the transaction request to the underlying engine?

[Copilot]

@copilot

Methods implemented as successful no-ops because IndexedDB manages transactions internally per operation
...

The current implementation provides API compatibility to prevent the error, but doesn't implement true transaction semantics.

IndexedDB's native transactions are synchronous and scope-based (auto-commit when execution context ends), which differs from AlaSQL's multi-step async pattern (BEGIN -> operations -> COMMIT/ROLLBACK).

To properly forward to IndexedDB, we'd need to implement transaction state management similar to LOCALSTORAGE:

• Keep operations in memory during transaction
• Persist to IndexedDB only on COMMIT
• Discard on ROLLBACK

Should I implement proper transaction support with this behavior? This would be a more significant change but would provide true transactional guarantees.

[mathiasrw]

@copilot

Yes, please provide transaction state management similar to LOCALSTORAGE. See if you can reuse across the two engines.

[Copilot]

@copilot

Yes, please provide transaction state management similar to LOCALSTORAGE. See if you can reuse across the two engines.

Implemented transaction state management similar to LOCALSTORAGE in commit 1ae1356:

Added helper functions:

• IDB.storeTable - Persists in-memory data to IndexedDB
• IDB.restoreTable - Loads data from IndexedDB to memory

Transaction behavior:

• When autocommit is OFF, data is loaded into memory on attach
• Operations work on in-memory data during transactions
• BEGIN ensures data is loaded in memory
• COMMIT persists all changes to IndexedDB
• ROLLBACK reloads data from IndexedDB, discarding changes

Shared pattern:
Both LOCALSTORAGE and INDEXEDDB now follow the same transaction model - operations on in-memory data with explicit persistence on commit. The helper functions have similar signatures but use storage-specific APIs (localStorage vs IndexedDB).