sys.stdin.read() exits the REPL process when stdin is set to be non-blocking on 3.14

Bug report

Bug description:

import sys
import os

os.set_blocking(sys.stdin.fileno(), False)
sys.stdin.read()

Just a weird side effect I found while ckecking out #109523 on Python 3.14 using the new REPL.
Running the code mentioned in #109523 raises a BlockingIOError and exits the REPL process.
Running the code from a script produces an error that is consistent with the previous report.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-121689

在 Linux 上新的 Python 3.14 REPL 中重现该代码片段，并将其与将相同代码作为脚本运行进行比较。审查 gh-121689 中链接的工作，并验证 BlockingIOError 不再退出 REPL 进程，同时脚本行为仍与早期报告一致。