fix(payment): restore accepted text after invalid amount input

frontend/src/components/payment/AmountInput.vue

@@ -88,8 +88,12 @@ function selectAmount(amt: number) {
 }
 
 function handleInput(e: Event) {
-  const val = (e.target as HTMLInputElement).value
-  if (!AMOUNT_PATTERN.test(val)) return
+  const input = e.target as HTMLInputElement
+  const val = input.value
+  if (!AMOUNT_PATTERN.test(val)) {
+    input.value = customText.value
+    return
+  }
   customText.value = val
   if (val === '') {
     emit('update:modelValue', null)

frontend/src/components/payment/__tests__/AmountInput.spec.ts

@@ -0,0 +1,37 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { enableAutoUnmount, mount } from '@vue/test-utils'
+import AmountInput from '../AmountInput.vue'
+
+vi.mock('vue-i18n', () => ({ useI18n: () => ({ t: (key: string) => key }) }))
+enableAutoUnmount(afterEach)
+
+function mountInput(value: number | null = null) {
+  return mount(AmountInput, { props: { modelValue: value } })
+}
+
+describe('recharge amount input', () => {
+  it.each(['10abc', '10.555', '-10', '1e2'])('restores the accepted amount after rejecting %s', async (value) => {
+    const wrapper = mountInput(10)
+    const input = wrapper.get('input')
+    await input.setValue(value)
+    expect((input.element as HTMLInputElement).value).toBe('10')
+    expect(wrapper.emitted('update:modelValue')).toBeUndefined()
+  })
+
+  it('restores the last typed amount rather than a stale prop', async () => {
+    const wrapper = mountInput()
+    const input = wrapper.get('input')
+    await input.setValue('12.50')
+    await input.setValue('12.500')
+    expect((input.element as HTMLInputElement).value).toBe('12.50')
+    expect(wrapper.emitted('update:modelValue')).toEqual([[12.5]])
+  })
+
+  it('preserves decimal editing and allows clearing the amount', async () => {
+    const wrapper = mountInput()
+    const input = wrapper.get('input')
+    for (const value of ['0', '0.', '0.5', '0.50', '']) await input.setValue(value)
+    expect(wrapper.emitted('update:modelValue')).toEqual([[null], [null], [0.5], [0.5], [null]])
+    expect((input.element as HTMLInputElement).value).toBe('')
+  })
+})