Distilled from the previous net/dataset experiment and the inline
closure version in check-ip. Keeps what actually earned its keep:
- Group ties one Fetcher to N views; a single Load drives all swaps,
so shared sources (one git pull, one zip download) don't get
re-fetched per view.
- View[T].Value() is a lock-free atomic read; the atomic.Pointer is
hidden so consumers never see in-flight reloads.
- Tick runs Load on a ticker with stderr error logging.
Dropped from the v1 design: MultiSyncer (callers fan-out inline when
needed), Close (unused outside geoip), Name (callers wrap the logger),
standalone Dataset type (Group with one view covers it), Sync vs Init
asymmetry (Load handles first-call vs update internally).
check-ip rewires to use it — file/git/http modes all build a Group
with two views, uniform shape.
check-ip and geoip no longer use it; formmailer now takes
*atomic.Pointer[ipcohort.Cohort] for Blacklist so callers own the
refresh + swap lifecycle directly. gitshallow doc comments that
referenced dataset.Syncer are trimmed.
The concepts the package tried to share (atomic-swap, group sync,
ticker-driven refresh) may come back under sync/dataset once we have
more than one in-tree caller that wants them.
- Each package gets its own go.mod: net/{dataset,httpcache,gitshallow,ipcohort,geoip,formmailer}
- go.work with replace directives for cross-module workspace resolution
- dataset.Syncer/NopSyncer moved here from httpcache; callers duck-type it
- dataset.View[T] returned by Add to prevent Init/Sync/Run misuse on group members
- cmd/check-ip moved from net/ipcohort/cmd/check-ip to top-level cmd/check-ip
- Add net/ipcohort/cmd/ipcohort-contains for standalone cohort membership testing
