0.3.0: backend::Store and parent-linked folder history

CHANGELOG.md

@@ -1,5 +1,95 @@
 # Changelog
 
+## Unreleased
+
+### Added
+
+- **Archived objects are a typed error.** A read the store refuses with
+  S3's `InvalidObjectState` (an object in GLACIER or DEEP_ARCHIVE that was
+  not restored) fails with `bigstore::backend::Error::Archived { key }`,
+  and in folder mode with the new `bigstore::folder::Error::Archived { key }`
+  (pull, log, and the history reads of push and status). Any other 403
+  stays the permission error it was. object_store exposes neither S3's
+  error code nor the storage class as data, so the code is read from the
+  error response it reports.
+- **Folder history is a graph of parent-linked versions.** Each record is
+  a DVC 3 `.dvc` pointer plus `meta: {bigstore: {parents, writer, time}}`,
+  stored create-once as `bigstore-history/<key>/<parents>/<id>.dvc`
+  (`<id>`: the first 32 hex characters of the SHA-256 of the record;
+  `<parents>`: `root`, or the parent ids sorted and `+`-joined, at most 8).
+  One listing gives the graph; the latest version is the only *head* (a
+  record no other follows). A record whose bytes do not hash to its name's
+  id, or whose parents differ from its name's, is refused as a bad record.
+- **Push checks the output's base**, the version its `.dvc` records in
+  `meta: {bigstore: {base: <id>}}`, before uploading anything. An output
+  equal to the only head adopts it and publishes nothing (this also
+  repairs a crash between the record and the `.dvc`). A `.dvc` without a
+  base that records the only head's content counts as based on it.
+  Otherwise push is refused with the new
+  `folder::Error::StaleBase { base, heads }` if there is no `.dvc` while
+  history has versions, or the base is not the only head;
+  and with `folder::Error::Diverged { heads }` if the history has forked,
+  unless `PushOptions::resolve` is `Resolve::Merge` (CLI:
+  `folder push --resolve merge`) and the base is one of the heads. The
+  record is published before the `.dvc`, which is written last. History is
+  then listed again: pushes that raced from the same base are reported in
+  `PushReport::forked_with` (a CLI warning).
+- `PushOptions::writer` (the host name by default) is recorded in each
+  version; `PushReport::version` is the version the output now is.
+- **Pull from history writes `<into>.dvc`** with the pulled version as its
+  base, last, once every file is in place; a cancelled or failed pull
+  leaves the old `.dvc`. A `.dvc` there that push would refuse to replace
+  is refused first. Pulling an older version makes the next push of it
+  `StaleBase`. `Selector::Latest` in a forked history is `Diverged`.
+- `SyncState::Stale { base, head }` and `SyncState::Diverged { heads }`;
+  `folder status` prints both. `folder log` prints each version's parents
+  and writer, and marks heads, fork points and merges.
+- `HistoryRecord` has `id`, `parents` and `writer` fields;
+  `HistoryRecord::output_id()` is the content id (manifest id or md5).
+- `bigstore::dvc::{RecordId, BigstoreMeta}`, and `DvcPointer::meta`: the
+  strict parser accepts exactly bigstore's two `meta:` shapes, and still
+  refuses any other `meta:` (so push never replaces a `.dvc` carrying
+  someone else's annotations).
+
+### Changed
+
+- **Breaking (library): `bigstore::backend::Store`** replaces the `Backend`
+  enum and the free functions `from_config`, `exists`, `put_bytes`,
+  `get_bytes`, `list`, `upload`, `download` and `download_verified`. Build
+  one with `Store::open(&cfg)` or `Store::from_object_store(client)`; its
+  methods are `head(key)` (size and modification time, `None` if absent;
+  replaces `exists`), `get(key, limit)`, `put(key, bytes)`,
+  `put_file(key, path)` (streamed, multipart above 10 MiB, aborted on a
+  failed read), `list(prefix)` (sorted `Listed { key, size, modified }`)
+  and `download_verified(key, expected, dir)`. The unverified `download` is
+  gone: the LFS adapter and `git bigstore pull` both download through
+  `download_verified`. `transfer::Remote::store` is now a `&Store`.
+- rclone remotes are listed with `rclone lsjson` instead of `rclone lsf`,
+  for object sizes and times; the keys listed are unchanged.
+- **Breaking (folder history): a hard cutover per history key.** 0.3 reads
+  0.2's `<time>-<content id>.dvc` records as a straight line in time order
+  (each with the id of its file name) and continues it, but never writes
+  that form; 0.2 clients do not see 0.3 records, so a 0.2 writer left on a
+  key forks it. Upgrade every writer of a key together. A `.dvc` 0.2 wrote
+  has no base; if it records the latest version's content, its output
+  counts as based on that version, so a changed output's first push
+  follows it. If it records an older version, the push is `StaleBase`.
+- **Breaking (library):** `HistoryRecord::id()` is gone: `id` is now the
+  record id, and `Selector::Id` (`--at <hex>`) matches record ids as
+  `folder log` prints them. Content ids still select 0.2 records (from the
+  md5 in their names), but not 0.3 ones. `Selector::AtOrBefore` uses
+  each record's own time and fetches every record. `SyncState::Diverged {
+  latest }` (changed locally and remotely) is now `Stale { base, head }`.
+  `PushOptions::cancel` stops a push before its record is published (it
+  was: before its `.dvc` was written).
+
+### Fixed
+
+- A read whose body ends before the object's length now fails with
+  `incomplete download of <key> (<got>/<expected> bytes)`. Before, a small
+  object (a `.dir` manifest or history record) was returned truncated, and
+  a download failed only as an integrity check.
+
 ## 0.2.1 — 2026-09-30
 
 ### Added

Cargo.toml

@@ -40,6 +40,7 @@ anyhow = "1"
 chrono = { version = "0.4", default-features = false, features = ["clock", "std"] }
 clap = { version = "4", features = ["derive", "env"], optional = true }
 futures = "0.3.32"
+gethostname = "1.1.0"
 globset = "0.4.18"
 hex = "0.4"
 indicatif = { version = "0.18.4", optional = true }