Describe the bug

If you have a process which outputs lots of logging on stdout and stderr, the nu docs say you could do "cmd out+err> [filename]" to pipe both into a file. This hangs and when you kill the process it ends up having around 64KB's of data in the output file flushed at the end, every time.

How to reproduce

1. Create a program called foo.c:

#include <stdio.h>

int main() {
	// Should emit 1MiB on stderr
	for (int i = 0; i < (1024 * 1024) / 16; i++) {
		fprintf(stderr, "0123456789ABCDE\n");
	}
}

2. Compile with gcc foo.c
3. Run with ./a.out out+err> /tmp/foo.txt
4. Observe that it hangs, exit and observe /tmp/foo.txt filesize
5. Run with ./a.out err> /tmp/foo.txt
6. Observe that it doesn't hang and observe /tmp/foo.txt filesize

Expected behavior

It shouldn't hang when mixing out+err> pipe form and should populate the file the same as in the err> pipe case.

Screenshots

No response

Configuration

Additional context

No response