CubeComming: manual imports of large hi-res Qobuz FLACs came out as empty
shells — no audio, no tags, no length/bitrate. Root cause: mutagen's in-place
save() rewrites the file, and it's NOT atomic; if the process is interrupted or
OOM-killed mid-write (he also reported the memory-growth issue #802), the file
is left truncated — audio and tags gone.
save_audio_file (the chokepoint both the enrichment tag-write AND wipe_source_
tags route through) now saves atomically: copy the original to a temp in the
same dir, write the modified tags into the copy, verify it's still valid audio
(duration > 0), then os.replace() it in. The original is untouched until that
atomic swap, so a crash can only orphan the temp — never destroy the user's
file. Falls back to the plain in-place save (byte-identical to before) when the
atomic path can't run, so nothing is ever left worse off. tag_writer's
write_tags_to_file routes through the same helper.
Verified the atomic path works with REAL mutagen on a real FLAC (audio length
preserved 1.0s→1.0s, tag written, temp cleaned). Tests: replace-on-success,
original-survives-save-failure, corrupt-temp-rejected, no-filename-plain-save,
+ a real-FLAC round-trip (skips without ffmpeg). 2443 import/metadata/tag tests
pass.
