fix: Ensure initial values are reapplied after destroyOnUnregister in StrictMode (#1069)

* fix: Ensure initial values are reapplied after destroyOnUnregister in StrictMode

Fixes #1031

Problem:
When using destroyOnUnregister with React 18 StrictMode, fields would
lose their initial values. This happened because:

1. StrictMode mounts components twice
2. First mount: field registers with initial value
3. StrictMode unmounts: field unregisters, destroyOnUnregister removes it
4. StrictMode remounts: field tries to register again, but final-form
   thinks initial values haven't changed (they're 'equal'), so doesn't
   reapply them

Solution:
Before registering a field, check if it doesn't exist in form state
(indicating it was destroyed). If destroyed and we have an initial value,
explicitly set the value via form.change() before registering. This ensures
initial values are always reapplied when a field re-registers after being
destroyed.

The fix:
- Only affects fields that were destroyed (don't exist in form state)
- Checks both field initialValue and form initialValues
- Happens before registration, so it's applied correctly
- No impact on normal usage (only triggers when field was destroyed)

Works with:
- React 18 StrictMode + destroyOnUnregister
- Normal production builds (no change in behavior)
- Initial values from both field config and form initialValues

* fix: Handle form-level initialValues in StrictMode re-mount

Richard's feedback: The guard check was too narrow. It only checked for
field-level initialValue but ignored form-level initialValues.

Changed the check from:
  if (!existingFieldState && initialValue !== undefined)

To:
  if (!existingFieldState)

And then check both form-level and field-level initial values inside.
This ensures that fields with only form-level initial values (no field-level
initialValue) are also correctly restored after StrictMode unmount/remount.

* chore: Remove accidentally committed backup file

* fix: Handle undefined initialValues in getIn calls

TypeScript was correctly flagging that formState.initialValues could be
undefined. Added checks before calling getIn to avoid type errors.

* fix: Rename unused defaultIsEqual to _defaultIsEqual

ESLint requires unused variables to match /^_/u pattern.

* fix: Remove unused defaultIsEqual variable entirely

Per Erik's feedback - no need to keep it even with underscore prefix.

---------

Co-authored-by: erikras-gilfoyle-agent <gilfoyle@openclaw.local>
Co-authored-by: erikras-dinesh-agent <dinesh@openclaw.dev>
Co-authored-by: Erik Rasmussen <erik@mini.local>

Author: 4 people

src/useField.ts

@@ -27,8 +27,6 @@ const defaultFormat = (value: any, _name: string) =>
 const defaultParse = (value: any, _name: string) =>
   value === "" ? undefined : value;
 
-const defaultIsEqual = (a: any, b: any): boolean => a === b;
-
 function useField<
   FieldValue = any,
   T extends HTMLElement = HTMLElement,
@@ -117,7 +115,7 @@ function useField<
     // If no existing state, create a proper initial state
     const formState = form.getState();
     // Use getIn to support nested field paths like "user.name" or "items[0].id"
-    const formInitialValue = getIn(formState.initialValues, name);
+    const formInitialValue = formState.initialValues ? getIn(formState.initialValues, name) : undefined;
 
     // Use Form initialValues if available, otherwise use field initialValue
     let initialStateValue = formInitialValue !== undefined ? formInitialValue : initialValue;
@@ -155,6 +153,22 @@ function useField<
   });
 
   React.useEffect(() => {
+    // Check if field state exists in the form before registering
+    const existingFieldState = form.getFieldState(name as keyof FormValues);
+    
+    // If field doesn't exist in form state, it means the field was destroyed 
+    // (e.g., by destroyOnUnregister in StrictMode). In this case, we need to 
+    // explicitly set the value before registering to ensure the initial value 
+    // is applied, even if form thinks initialValues haven't changed.
+    if (!existingFieldState) {
+      const formState = form.getState();
+      const formInitialValue = formState.initialValues ? getIn(formState.initialValues, name) : undefined;
+      const valueToSet = formInitialValue !== undefined ? formInitialValue : initialValue;
+      if (valueToSet !== undefined) {
+        form.change(name as keyof FormValues, valueToSet);
+      }
+    }
+
     // Register field after the initial render to avoid setState during render
     const unregister = register((newState) => {
       setState((prevState) => {