removeValue on array field incorrectly sets isTouched=true on all shifted siblings #2131

Describe the bug

Calling form.removeValue(index) on an array field flips isTouched to true on every sibling at index ≥ removed index. Even when the user has never interacted with those fields.

The bug lives in @tanstack/form-core, so every adapter (react, vue, solid, svelte, angular, lit) is affected.

Your minimal, reproducible example

https://github.com/ntatoud/repro-tanstack-form-removevalue-touched.git

Steps to reproduce

1. git clone https://github.com/ntatoud/repro-tanstack-form-removevalue-touched.git
2. npm install && npm run test (deterministic vitest assertion)
3. npm run dev
4. Click 'remove index 2' button.
5. Notice how all shifted elements are not marked as touched.

Expected behavior

isTouched stays false on every remaining item: The user never touched anything.

values  = ['a', 'b', 'd', 'e']
touched = [false, false, false, false]

How often does this bug happen?

Every time

Screenshots or Videos

Platform

• OS: macOS 26.2
• Node: 24.15.0
• Browser: any (not related to browser)

TanStack Form adapter

react-form

TanStack Form version

1.29.0

TypeScript version

6.0.2

Additional context

Adapter-agnostic: bug is in form-core, not the React bindings

Proposed fix

In validateArrayFieldsStartingFrom, bypass validateField when the field already has a mounted instance and call fieldInstance.validate(cause) directly. This preserves validation, skipping the auto-touch:

// packages/form-core/src/FormApi.ts
batch(() => {
  fieldsToValidate.forEach((nestedField) => {
    fieldValidationPromises.push(
      Promise.resolve().then(() => {
        const fieldInstance = this.fieldInfo[nestedField]?.instance
        if (fieldInstance) {
          return fieldInstance.validate(cause)
        }
        return this.validateField(nestedField, cause)
      }),
    )
  })
})

Verified locally by patching node_modules/@tanstack/form-core/dist/esm/FormApi.js.

The same fix likely applies to swapFieldValues / moveFieldValues / insertFieldValue if they call validateArrayFieldsStartingFrom (worth auditing as a follow-up)