iOS: clear and fill on a field over 120 characters leave old text behind (estimatedDeleteCount caps at 120) #3851

On iOS, fill <target> "" and fill <target> "<text>" delete at most 120 characters of the existing value. A longer value is only partly cleared, so a clear leaves text behind and a fill appends to the leftover instead of replacing it.

Reproduce

1. A SwiftUI TextEditor (or any text field) holding 501 characters.
2. fill <field> "": 381 characters remain.
3. Put 501 characters back, then fill <field> "<500 chars>": the field ends at 1261 characters and the fill fails text entry verification.

Seen on agent-device 0.21.28, iOS 26.5 simulator. The same code is on main (e35d8de).

Cause

RunnerTests+TextEntry.swift:

private func estimatedDeleteCount(for element: XCUIElement) -> Int {
  let valueText = normalizedElementText(element.value)
  let base = valueText.isEmpty ? 24 : (valueText.count + 8)
  return max(24, min(120, base))
}

clearTextInput sends that many delete keys once and never checks whether the field is empty afterwards. With 501 characters:

• clear: 501 - 120 = 381 left
• fill: 381 + 500 = 881, then the repair in RunnerTests+TextTyping.swift (clearTextInput(app: app, repairTarget) before typeText(expectedText)) deletes another 120 and retypes 500: 881 - 120 + 500 = 1261

Suggested fix

In clearTextInput, re-read the value after each delete burst and keep going until it reads empty, with a bounded number of rounds so a field that never reports its value can't loop forever. Size each burst from the value just read (keep a per-burst cap if long typeText strings are slow). When the value can't be read (secure fields, bullet-only values), fall back to the current single burst, or to select-all then delete.