forms: custom FormValueControl ignores updateOn ('blur' / 'submit') in reactive and template-driven forms

Start in Angular's forms package and reproduce the behavior using the linked minimal reproduction. Trace how FormValueControl and FormCheckboxControl connect to Reactive Forms and Template-Driven Forms, then add focused coverage for updateOn set to 'blur' and 'submit'. Done means custom controls defer FormControl or ngModel updates until the configured event, matching legacy ControlValueAccessor behavior.

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

forms

Is this a regression?

No

Description

Custom components implementing Signal Forms FormValueControl<T> (or FormCheckboxControl) without a legacy ControlValueAccessor ignore the updateOn configuration ('blur' or 'submit') when bound to Reactive Forms ([formControl], formControlName) or Template-Driven Forms ([(ngModel)] with [ngModelOptions]).
Instead of deferring the update until blur (touch output) or form submission, the bound FormControl or ngModel updates immediately on every keystroke/emission from the custom control's model() signal.

This breaks a migration path to FormValueControl since it means that switching the implementation of the custom control can break the usage. The assumption in the docs is therefore wrong.

Please provide a link to a minimal reproduction of the bug

https://github.com/sbarfurth/signal-control-update-on

Please provide the exception or error you saw

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

Angular CLI       : 22.1.8
Angular           : 22.1.6
Node.js           : 24.19.0
Package Manager   : npm 11.17.0
Operating System  : linux x64
┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package                   │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build            │ 22.1.8            │ ^22.1.8           │
│ @angular/cli              │ 22.1.8            │ ^22.1.8           │
│ @angular/common           │ 22.1.6            │ ^22.1.0           │
│ @angular/compiler         │ 22.1.6            │ ^22.1.0           │
│ @angular/compiler-cli     │ 22.1.6            │ ^22.1.0           │
│ @angular/core             │ 22.1.6            │ ^22.1.0           │
│ @angular/forms            │ 22.1.6            │ ^22.1.0           │
│ @angular/platform-browser │ 22.1.6            │ ^22.1.0           │
│ @angular/router           │ 22.1.6            │ ^22.1.0           │
│ rxjs                      │ 7.8.2             │ ~7.8.0            │
│ typescript                │ 6.0.3             │ ~6.0.2            │
│ vitest                    │ 4.1.11            │ ^4.0.8            │
└───────────────────────────┴───────────────────┴───────────────────┘

Anything else?

No response