Fiori Source Code assets versioning and protection

I worked full time in a ReactJS Project where 4 developers were involved.

We did everything in a github private repository.

Leader did the Ci Cd and deployed.

How is this done in SAP Fiori/SAP-UI5?

I have used deploy in a test server and seen "objects" go to SAP BSP application object. Fiori/UI5 app seem well integrated with CTS but what about the source code in snippets that remain in DEVSPACE for BAS or PC in case of VSCODE. Or the sequence of "generation" that yeoman has done.

How are source code assets protected and kept centrally?

How is source code versioned esp when multiple deployers working on same Fiori App.

As I have experience in ABAP I look for the same "comfort" of integration with CTS for source and objects generated js xml yaml etc.

Generated code esp for fiori elements means all js files etc. may not reverse engineer the sequemce of screens the developer have have navigated. This lack of production developer sync may be a problem?
ABAP Objects and SmartForms stay inside the server in on-premise.
But in BTP what happens?
What if a developer quits and another assigned maintenance task of Fiori elements?

I suppose organization has to depend on any documentation programmer has done?

Searched a lot but could not find any clear document covering the above questions/concerns.
Please help clarify my doubts.

Regards
Jayanta