Crate uni_sidecar 

Atomic JSON sidecar for _system/ state files.

Several uni-db subsystems persist a small document under <data_path>/_system/<name>.json — the CDC checkpoint table, the deferred- trigger queue, the background-job scheduler (in uni-plugin-host), and the declared-plugins registry (in uni-plugin-custom). They all want the same thing: load the whole document at startup (treating a missing or empty file as “nothing yet”), and replace it atomically on every write. This crate is the single, correct implementation of that pattern, shared so no subsystem re-rolls it.

“Atomic” here means write-to-temp, fsync the temp file, then rename over the target. Crucially it also fsyncs the parent directory after the rename: on POSIX a rename is not crash-durable until the directory entry is flushed, so without it a power loss can leave the file reverted to its pre-rename contents even though the data was synced.

SystemSidecar handles only the IO. Higher-level concerns — write serialization (a mutex spanning read-modify-write), a best-effort Cypher mirror, per-row re-binding — stay with the callers, which compose them around SystemSidecar::load / SystemSidecar::store.

Structs

SystemSidecar

Atomic JSON persistence for one _system/ document of type T.

VecSidecar

Atomic JSON sidecar specialized to a Vec<T> document — the shape every _system/ row table uses (CDC checkpoints, scheduler jobs, deferred triggers, declared plugins).

Enums

SidecarIoError

Error raised by SystemSidecar load/store operations.