lib.backup() now waits for an ML data fetch, joining the one its refresh
started or starting one, before it writes the per-file JSON, and each
file's JSON carries the cached payload as mlData. When the fetch fails,
each file with no cached ML data gets mlDataError and an entry in
failures.json, so the result counts it as failed and quak backup exits 1;
the next run fetches again.
Judgement call: the wait comes after the originals are downloaded, so the fetch runs alongside the downloads.
Judgement call: a failed ML fetch is recorded per file in failures.json, which is how the exit code goes non-zero without changing src/cli-commands.ts.
Model: opus-5-5
sneak