Module checkpoint 

Checkpoint references — atune moves references, never bytes.

The checkpoint contract is deliberately narrow: atune never interprets checkpoint bytes. The guide shows it in use under population-based training. A trial records a reference — a run-directory path, an artifact id, whatever string its objective wrote — at a resource step, and the framework only ever stores that reference and later hands it back to a Fork or a resume of the trial. oniro’s run-dir checkpoints plug in as references without conversion.

Where the reference lives

A trial’s checkpoint references ride a typed StateBlob on a Scope::Named slot keyed by the trial id (checkpoint_scope). Retry, fan, constraint, and checkpoint resources all use independent named keys; Scope::Trial remains only as a read-compatible home for historical retry/fan v1 data.

Recording is done through TrialCtx::record_checkpoint and read back through Study::trial_checkpoints / Study::latest_checkpoint. A study that never records a checkpoint writes no checkpoint state.

Replicates of a multi-seed fan keep their own references

Each replicate of a SeedProtocol fan is a separate run, so a reference one replicate records must not replace another’s. Inside a fan, a recorded reference is kept under its replicate index in TrialCheckpoints::replicates as well as in the trial-level refs, whose meaning is unchanged: the most recent reference recorded at each step. A replicate resumes from its own latest reference when the source trial has one, and from the trial-level latest otherwise. The field is optional in the version-1 payload: a blob without it reads as having no replicate references, and a reader that predates it ignores it and still sees refs.

Structs

TrialCheckpoints

The checkpoint references a trial has recorded, keyed by resource step.

Constants

CHECKPOINT_BLOB_KIND

The kind tag of a trial’s checkpoint-reference state blob.

CHECKPOINT_BLOB_VERSION

The schema version of the CHECKPOINT_BLOB_KIND payload (TrialCheckpoints).

Functions

checkpoint_scope

The Scope a trial’s checkpoint references are stored under.