Fix ft_dataset write_results dropping messages and opening output in binary mode

[Chessing234]

Bug

write_results in python/dolma/core/ft_dataset.py:

with smart_open.open(config.out_path, "wb") as o:
    while True:
        msg = q.get()

        if msg == _WRITER_EXIT_MSG:
            break

        if not flag.is_set():
            o.write(q.get())
            o.write("\n")
            written += 1

Two bugs in five lines:

1. o.write(q.get()) calls q.get() a second time, so the msg retrieved at the top of the loop is discarded (only used for the exit check) and a fresh message is pulled and written. Every other producer message is silently dropped, and the write itself can even pull and write the _WRITER_EXIT_MSG sentinel ("__WRITE__EXIT__") into the output file, leaving the writer blocked on the next q.get().

2. The file is opened with mode "wb" (binary), but the producer (process_file) puts plain str values on the queue (q.put(f"__label__{label} {final_text}")) and line 112 writes the literal "\n". Both calls raise TypeError: a bytes-like object is required, not 'str' the moment any record is produced.

Root cause

1. Typo / copy-paste: the retrieved msg was never written — q.get() was called twice.
2. Mode mismatch between the opened file (binary) and the str payloads produced upstream.

Fix

• Write the already-retrieved msg (o.write(msg)).
• Open the output path in text mode ("w") to match the str payloads.

No change to the sentinel-based shutdown or the flag-based early-exit logic.