# appcore-sync
[Minimal example](examples/basic.en.md) |
[Intermediate example](examples/intermediate.en.md)
**Responsibility:** conservative leader-to-follower replication contracts and
local durability helpers.
**Internal dependencies:** `appcore-core`, `appcore-distributed-contracts`,
`appcore-ops`, `appcore-transport`.
**Primary API:** node role/status/peer/heartbeat and `SyncMessage`; V1 wire
codec; replication logs and snapshots; in-memory/file checkpoints and outbox;
receiver state/acknowledgement; follower client; HTTP transport; peer discovery;
retry policy, push metrics and `SyncError`.
Opaque content-envelope transport contracts are reexported for DNT-backed sync
packages without exposing plaintext to routing code.
Use it for compatible, ordered, hash-chained replication. Do not bypass
identity/protocol checks or reinterpret it as RAFT, multi-master consensus or a
business conflict resolver.
The file log is capped at 256 MiB and the outbox at 64 MiB. Checkpoint peer IDs
and hashes are validated on write and load. A receiver validates the complete
batch, sequence arithmetic and every record bound before any log or checkpoint
mutation, so a late invalid event cannot leave a partial append.
**Maturity:** stable conservative RC profile with strict V1 decoding.