fix: ensure isValid updates after trigger() when accessed later

[jtomaszewski]

Summary

Fixes an issue where formState.isValid doesn't update correctly after calling setValue() with { shouldValidate: true } or after trigger(), even when:

• trigger() returns true
• formState.errors is empty {}
• The form values are valid according to the schema

Root Cause

The proxy in getProxyFormState reads from React state, but when isValid isn't subscribed (accessed) before trigger() is called, the React state isn't updated. This causes stale values when isValid is accessed later.

Fix

1. In createFormControl.ts trigger(): Store the computed isValid value in _formState.isValid after the notification is emitted
2. In getProxyFormState.ts: For the isValid key, return the value from control._formState directly, which always has the most up-to-date value

The _formState.isValid update is placed AFTER _subjects.state.next() to preserve the existing notification condition that compares isValid with _formState.isValid.

Test Plan

• Added test case that reproduces the bug scenario (accessing isValid after trigger() without prior subscription)
• Added tests for setValue + trigger with built-in validation
• Added tests for useFieldArray scenarios
• All existing tests pass (1037 tests)

Related Issues

This is the same issue reported in:

• issue: the field change is not registered if you insert a value into the field #12684
• issue: revalidateMode: "onSubmit" does not work correctly with useFieldArray #12631

🤖 Generated with Claude Code

[jtomaszewski]

Raised this too early, will get back if I get a good repro (and maybe a fix).