Train Artifact Storage Reference

Status: canonical PSI-285 / #3590 reference record, updated 2026-03-14 after landing the train artifact-storage layer in crates/psionic-train/src/artifact_storage.rs.

This document records the first explicit storage-lifecycle contract for train artifacts inside Psionic.

Canonical Runner

Run the artifact-storage harness from the repo root:

scripts/release/check-psionic-train-artifact-storage.sh

What Landed

psionic-train now owns a typed artifact-storage controller that tracks checkpoint, rollout, eval, and log artifacts through retention, archival, deduplication, garbage collection, and cold restore.

The new typed surfaces include:

• TrainArtifactClass
• ArtifactRetentionProfile
• ArtifactArchiveClass
• TrainArtifactLocator
• TrainArtifactRecord
• ArtifactStorageTransition
• ArtifactStorageSweepReceipt
• ArtifactColdRestoreReceipt
• TrainArtifactStorageController

What The Contract Makes Explicit

The artifact-storage layer now makes these train-specific lifecycle seams machine-legible:

• class-scoped retention thresholds for hot and warm tiers
• explicit archival posture for ephemeral, restorable, and immutable artifacts
• digest-aware deduplication instead of implicit operator cleanup
• typed lifecycle state for active, restore-requested, and garbage-collected artifacts
• sweep receipts that explain every migration or deletion transition
• cold-restore receipts with restore-SLA targets

Pass Criteria

The artifact-storage layer is green only if all of the following remain true:

• checkpoint artifacts can progress from hot storage to warm, then archive, and finally garbage collection when policy allows
• duplicate rollout digests can be identified and removed deterministically
• archived eval artifacts can request and complete cold restore through typed receipts
• storage decisions remain inspectable through typed records and receipts rather than logs alone

Current Limits

This issue does not claim that train storage is complete. It does not yet implement:

• an external blob-store client or remote archival backend
• policy synchronization with kernel or Nexus authority services
• byte-accurate cost accounting or queue-budget interaction
• artifact placement optimization across hosts or storage media

What it does do is give Psionic one Rust-owned storage lifecycle surface for artifact retention, deduplication, archival, garbage collection, and cold-restore truth.

Remote Backend Extension

XTRAIN-8 extends the older local controller with one provider-neutral remote backend layer in crates/psionic-train/src/remote_artifact_backend_contract.rs, the generator binary remote_train_artifact_backend_contract, the checker scripts/check-remote-train-artifact-backend-contract.sh, the focused reference doc docs/REMOTE_TRAIN_ARTIFACT_BACKEND_REFERENCE.md, and the fixture fixtures/training/remote_train_artifact_backend_contract_v1.json. That layer adds a shared remote backend trait, concrete Google and RunPod backends, byte-accounted placement policy, typed restore policy, and finalizer projections for checkpoints, logs, metrics bundles, and final evidence bundles.