Field-level `onMount` errors are never cleared on linked-field revalidation

Describe the bug

When a field has a field-level onMount validator and is linked to another field, the onMount error is never cleared, even when the other validators on that field run successfully via the linked-field mechanism and report the field as valid.

The result is that field.state.meta.errors keeps surfacing the stale mount-time error and isValid stays false indefinitely or until you touch the field. This also propagates to form.state.isValid, breaking submit-button enablement and any UI that depends on per-field validity.

Possibly related to #689, #903

Your minimal, reproducible example

https://stackblitz.com/edit/vitejs-vite-ywiic5qt?file=src%2FApp.tsx

Steps to reproduce

1. Open the StackBlitz repro.
2. Observe the initial state: password is empty, confirmPassword defaults to "password". The confirmPassword field's onMount validator correctly reports "Passwords do not match" in errorMap.onMount, and isValid is false. This is expected.
3. Type "password" into the Password input. Do not touch the Confirm Password input.
4. The onChange validator on confirmPassword runs via onChangeListenTo: ["password"] and correctly returns undefined — errorMap.onChange is now undefined.
5. Bug: errorMap.onMount still shows "Passwords do not match", and both confirmPassword.isValid and form.isValid remain false, even though both validators on the field, given the current values, return undefined.

Expected behavior

As a user, I expected the onMount error to clear once the field's other validators run successfully via the linked-field mechanism, but I am seeing the onMount error persist indefinitely (or until it's touched), leaving the field marked as invalid even though all of its validators agree that it is valid.

How often does this bug happen?

Every time

Platform

• OS: macOS
• Browser: Google Chrome
• Version: 146.0.7680.178

TanStack Form adapter

react-form

TanStack Form version

v.1.29.0

TypeScript version

v6.0.2

Additional context

Not sure whether to classify this as a bug or a design choice. onMount only clearing on direct value changes could be a deliberate "the user must acknowledge this field" rule. But it does feel like an edge case worth revisiting, given that onChangeListenTo / onBlurListenTo exist specifically for cross-field patterns.

If the current behavior is intentional, an opt-in to let successful linked-field revalidation clear the stale onMount slot would be very helpful. The only workaround I've found is to manually clear the slot via setMeta from a listener on the source field, which is fragile and easy to forget.

Start with the linked-field revalidation flow in the StackBlitz reproduction, focusing on onMount, onChangeListenTo, errorMap, and field state validity. Confirm that changing password successfully revalidates confirmPassword; done means the stale onMount error is cleared and both field.isValid and form.isValid become true without touching confirmPassword.