Extract controlled field array logic into reusable hook

[gilgardosh]

Summary

Refactors repeated field array control logic across multiple components into a new useControlledFieldArray hook. This hook wraps useFieldArray and merges registered fields with watched values, ensuring components always render current values while maintaining stable field IDs.

Key Changes

• New hook: useControlledFieldArray in packages/client/src/hooks/use-controlled-field-array.ts

  • Encapsulates the pattern of watching field array values and merging them with registered fields
  • Exports FieldArrayItem type to replace the now-shadowed FieldArray type from react-hook-form v7.82+
  • Returns controlledFields, append, remove, and watchFieldArray

• Updated components to use the new hook:

  • FlightPathInput
  • StringArrayInput
  • ChargeSpreadInput
  • AttendeesStayInput

• Type safety improvements: Replaced casts using the deprecated FieldArray type with the new FieldArrayItem type

Implementation Details

The hook eliminates boilerplate by automatically:

1. Calling useFieldArray with the provided control and array path
2. Watching the field array values
3. Merging watched values with field metadata (preserving stable IDs)
4. Returning the merged fields alongside append and remove actions

This ensures all components render always-current values from the form state while keeping field IDs stable for React reconciliation.

https://claude.ai/code/session_01UAZSFDb2GcgSmp5uXhy4w8

[gemini-code-assist]

Code Review

This pull request introduces a new custom hook, useControlledFieldArray, which encapsulates the logic of wrapping useFieldArray and merging registered fields with watched values. This hook is then integrated into several input components (AttendeesStayInput, FlightPathInput, ChargeSpreadInput, and StringArrayInput) to reduce boilerplate and unify behavior. Feedback on the hook highlights a critical bug where spreading primitive values (like strings) inside an object literal pollutes the returned object, and suggests improving type safety by genericizing the hook's path parameter.

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