bug(matDatePickerInput): invalid values are not cleared on control.reset #33978

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

Problem

When the default value of a date input is empty, calling control.reset() (which can be called directly or by a parent) does not clear invalid text.

This may be a dupe of #33610 which was closed due to inactivity

Potential Cause

Looks like this may have introduced by a change in the writeValue function on MatDatepickerInputBase

The below will no longer format the input field if the control value is currently empty and the input has invalid text.

  writeValue(value: D): void {
    // We produce a different date object on each keystroke which can cause signal forms'
    // interop logic to keep calling `writeValue` with the same value as the user is typing.
    // Skip such cases since they can prevent the user from typing (see #32442 and #32475).
    this._assignValueProgrammatically(value, value !== this.value);
  }

  protected _assignValueProgrammatically(value: D | null, reformat: boolean) {
    value = this._dateAdapter.deserialize(value);
    this._lastValueValid = this._isValidValue(value);
    value = this._dateAdapter.getValidDateOrNull(value);
    this._assignValue(value);

    // date adapter turns invalid dates to null so `reformat` from `writeValue` is false
    if (reformat) {
      this._formatValue(value);
    }
  }  

In previous versions, _formatValue would always be called.

Reproduction

StackBlitz link: https://stackblitz.com/edit/1hicipgd

Steps to reproduce:

1. Enter in any invalid date text into the field tied to a form control
2. Call control.reset() (Reset Datepicker button in StackBlitz)

Expected Behavior

Control should reset to default value (empty in this case) and the invalid input text should be cleared

Actual Behavior

Invalid value text remains in the input

Environment

• Angular: 22.2.0
• CDK/Material: 22.2.0
• Browser(s): Chrome 155.0.8059.85
• Operating System: Windows