ROOT interpreter doesn't handle `<Insert>` key properly at the prompt

[amadio]

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Description

When the <Insert> key is pressed within an interactive session, only one character can be typed/seen at a time, so the prompt doesn't work correctly. Pressing the key again restores normal behavior.

Reproducer

~ $ root --version
ROOT Version: 6.38.00
Built for linuxx8664gcc on Feb 25 2026, 09:57:44
From tags/6-38-00@6-38-00
~ $ root.exe
   ------------------------------------------------------------------
  | Welcome to ROOT 6.38.00                        https://root.cern |
  | (c) 1995-2025, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for linuxx8664gcc on Feb 25 2026, 09:57:44                 |
  | From tags/6-38-00@6-38-00                                        |
  | With  std201703                                                  |
  | Try '.help'/'.?', '.demo', '.license', '.credits', '.quit'/'.q'  |
   ------------------------------------------------------------------

root [0] // press <Insert> key after this comment, then try to .q to quit
root [1] q
input_line_10:2:3: error: use of undeclared identifier 'q'
 (q)
  ^
Error in <HandleInterpreterException>: Error evaluating expression (q)
Execution of your code was aborted.
root [2] // pressing <Insert> key again "fixes" the problem
root [3] // only one character can be seen at a time when <Insert> is active

ROOT version

6.38.00

Installation method

emerge

Operating system

Gentoo Linux

Additional context

No response