Regression: 3.13 `traceback.format_list()` breaking behavior change.

Bug report

Bug description:

traceback.format_list() no longer works with lines that have breaks in them:

import traceback
import sys

print(f"Python {sys.version_info.major}.{sys.version_info.minor}")

# Frame with multiline text (source + variable annotations)
frames = [('test.py', 10, 'func', 'x = foo + bar\n\t\thello\n\tworld')]

print("\nInput (3 lines):")
print(repr(frames[0][3]))

print("\nOutput from traceback.format_list():")
result = traceback.format_list(frames)[0] # Yes, it't always a 1-element list both on 3.12 adn 3.13.
print(result)

Python 3.12

Input (3 lines):
'x = foo + bar\n\t\thello\n\tworld'

Output from traceback.format_list():
  File "test.py", line 10, in func
    x = foo + bar
                hello
        world

Python 3.13

Input (3 lines):
'x = foo + bar\n\t\thello\n\tworld'

Output from traceback.format_list():
  File "test.py", line 10, in func
    x = foo + bar

This broke bettre_exceptions on 3.13, which was fixed by formatting the traceback manually. Can we either

• Revert to old behavior in 3.15 and maybe document that it was broken in 3.13 and 3.14?
• Document the behavior change?

ref: https://github.com/Qix-/better-exceptions/issues/134

CPython versions tested on:

3.13

Operating systems tested on:

No response

Linked PRs

• gh-153469

Reproduce the supplied script with Python 3.12 and 3.13, then start at traceback.format_list(). Review linked PR gh-153469 and the surrounding traceback behavior before choosing whether compatibility or documentation is intended. Done means the accepted behavior is implemented or documented and the multiline case is covered by the relevant tests.