Which @angular/* package(s) are the source of the bug?

core

Is this a regression?

No

Description

Hey,
I've noticed that on each page load, after Angular initializes, all element attributes get re-rendered. This is easy to see with the "Rendering -> Paint flashing" option enabled in dev tools & console.logs from mutation observer.

I've added an app initializer that blocks rendering for 1 second and registers a mutation observer to track all attribute changes:

provideAppInitializer(()=>{returnnewPromise((resolve)=>{if(typeofwindow!=='undefined'){// mutation observer for console.logs}setTimeout(()=>{resolve(true);},1000);});})

According to thedocs:

Hydration is the process that restores the server-side rendered application on the client. This includes things like reusing the server rendered DOM structures, persisting the application state, transferring application data that was retrieved already by the server, and other processes.

Do I understand correctly that in this case, hydration simply doesn't work?

Please provide a link to a minimal reproduction of the bug

https://github.com/zip-fa/ng20-hydration-issue

Please provide the exception or error you saw

Please provide the environment you discovered this bug in (runng version)

Angular: 20.1.1... common, compiler, compiler-cli, core, forms, localize... platform-browser, platform-server, routerPackage                      Version------------------------------------------------------@angular-devkit/architect    0.2001.0@angular-devkit/core         20.1.1@angular-devkit/schematics   20.1.1@angular/build               20.1.1@angular/cli                 20.1.1@angular/ssr                 20.1.1@schematics/angular          20.1.1rxjs                         7.8.2typescript                   5.8.3

Anything else?

ng build && node dist/ng20-hydration-issue/server/server.mjs