Pure formatter drift picked up after running ruff format across the
tree. No behavioural changes: line-length unwrapping where strings
fit on one line, one blank-line separator added to _model.py.
One shared CURRENT_VERSION across the three top-level serialised
payloads (VideoPredictions, JobResults, BenchmarkResult), with
per-schema registries populated via register_*_migration(from_version)
decorators. FutureSchemaError and MigrationNotFoundError surface bad
chains clearly. CURRENT_VERSION=2 with v1→v2 migrations registered
that add an optional provenance field to the payload dicts.
Tested standalone; io.py is wired through the migrator in a follow-up
commit that introduces the Provenance schema those migrations target.
Levi Neuwirth