🐞[BUG]:Mutating selector data unexpectedly modifies the state without dispatching an action

[lgorecki]

Affected Package

@ngxs/store >= 18.1.5

Is this a regression?

Not sure

Description

Mutating selector data unexpectedly modifies the state without dispatching an action.

I encountered an issue where data retrieved from a selector was unintentionally modified by an Angular form control, leading to unintended state changes. My assumption was that selectors should return immutable data, preventing direct state modifications. However, this behavior suggests that the selector's return value is mutable, causing state mutations without explicit actions.
Found similar issue on StackOverflow from 4 years ago where the answer claims that it should at least complain in devmode that it is readonly but there are no such notifications. https://stackoverflow.com/questions/66563574/angular-mutating-ngxs-selector-data-is-modifying-state-without-an-action

Best case scenario I believe that NGXS selectors should be immutable or at least readonly so we can get warning that we are modifying readonly data. If the official statement is that developers should decide when to make selector immutable please share some guidelines on this matter because from my experience it destroys any optimization for selectors done in the library and makes them run much more often than they should.

🔬 Minimal Reproduction

A reproducible example is available here:
StackBlitz Demo

(even better to check on own app with redux tools)

Note: The provided example demonstrates a bad pattern but illustrates the issue I encountered. In my actual application, I retrieved data from a selector and passed it to an Angular form. Unexpectedly, one of the form controls modified an object inside array within the selector’s data, affecting the application state without an explicit action dispatch.

🔥 Exception or Error

No error

Environment

Libs:
- @angular/core version: 18.2.13
- @ngxs/store version: 18.1.6