Address the completion review findings on top of the upstream review
fixes:
- Store runs on the engine's checkpoint goroutine without the task
lock and serializes the returned value afterwards: take the fetcher
mutex and return a deep copy instead of the live state pointer,
matching the HTTP protocol's Store pattern
- Load the journal and per-run base counters before publishing the run
as active, so Stats/Progress never observe half-initialized fields
- Bind the journal fingerprint to the key IV as well: a rotated IV on
an otherwise identical plan would silently decrypt to garbage
- Keep every EXT-X-MEDIA member per group instead of only the first
one, so a group with a URI on a later member is still detected
- After a merge that raced with a pause, keep the staged segments and
exit silently instead of cleaning them up; drop a dead context
check and an unused helper, and make the MAP identity and merge
part-file names unambiguous
- Give every task a random staging identity persisted in the saved
state: two tasks downloading the same playlist into the same
directory get separate segment folders and journals instead of
deleting each other's progress
- Bind the journal to a fingerprint of the full download plan (media
URL, ordered segments, ranges, keys); foreign or unreadable journals
are discarded rather than applied to the wrong segments, and the
ledger is rewritten through a temp file + rename
- Legacy states without a staging identity migrate to a fresh folder
instead of reusing the shared URL-hash folder
- Merge into a unique temporary file next to the target, check write
and close errors, then remove-then-rename over the final name: a
failed merge preserves the staged segments for a retry and re-merging
after a crash stays idempotent
- Drop the staging folder when a URL patch invalidates the plan
sun