Retry some writes on EINTR again

I guess?
Fixes f0e007c439 (Relocate tty metadata and protocols and clean it up,
2025-06-19).

src/common.rs

@@ -1355,7 +1355,7 @@ pub fn valid_func_name(name: &wstr) -> bool {
 
 /// A rusty port of the C++ `write_loop()` function from `common.cpp`. This should be deprecated in
 /// favor of native rust read/write methods at some point.
-pub fn write_loop<Fd: AsRawFd>(fd: &Fd, buf: &[u8]) -> std::io::Result<()> {
+pub fn safe_write_loop<Fd: AsRawFd>(fd: &Fd, buf: &[u8]) -> std::io::Result<()> {
     let fd = fd.as_raw_fd();
     let mut total = 0;
     while total < buf.len() {
@@ -1374,6 +1374,8 @@ pub fn write_loop<Fd: AsRawFd>(fd: &Fd, buf: &[u8]) -> std::io::Result<()> {
     Ok(())
 }
 
+pub use safe_write_loop as write_loop;
+
 // Output writes always succeed; this adapter allows us to use it in a write-like macro.
 struct OutputWriteAdapter<'a, T: Output>(&'a mut T);
 

src/tty_handoff.rs

@@ -1,7 +1,7 @@
 //! Utility for transferring the tty to a child process in a scoped way,
 //! and reclaiming it after.
 
-use crate::common;
+use crate::common::{self, safe_write_loop};
 use crate::flog::{FLOG, FLOGF};
 use crate::global_safety::RelaxedAtomicBool;
 use crate::job_group::JobGroup;
@@ -18,7 +18,6 @@
 use crate::wutil::perror;
 use libc::{EINVAL, ENOTTY, EPERM, STDIN_FILENO, WNOHANG};
 use std::mem::MaybeUninit;
-use std::os::fd::BorrowedFd;
 use std::sync::atomic::{AtomicBool, AtomicPtr, AtomicU8, Ordering};
 
 // Facts about our environment, which inform how we handle the tty.
@@ -316,8 +315,7 @@ pub fn safe_deactivate_tty_protocols() {
 
     let commands = protocols.safe_get_commands(false);
     // Safety: just writing data to stdout.
-    let stdout_fd = unsafe { BorrowedFd::borrow_raw(libc::STDOUT_FILENO) };
-    let _ = nix::unistd::write(stdout_fd, commands);
+    let _ = safe_write_loop(&libc::STDOUT_FILENO, commands);
     TTY_PROTOCOLS_ACTIVE.store(false, Ordering::Release);
 }