Module save 

Save persistence with versioned migration chain.

Wire format on disk: a single JSON object with a "version": u32 field. Pre-versioned saves (no field) are treated as V1 by migrate::peek_version. Each version has a frozen struct in versions/vN.rs and a conversion into the next version’s struct, walked end-to-end on load.

Once shipped, a versions/vN.rs is FROZEN. New schema changes go in vN+1.rs together with a From<vN> for vN+1 impl and a unit test. See the “Save versioning” section in CLAUDE.md for the full policy.

Callers (the Persistence impls under platform/) should never touch serde_json on GameState directly — go through load_from_str / save_to_string so the version dispatch stays in one place.

Modules

migrate

Version-peeking helper for the save migration chain.

versions

Frozen save schemas — one module per shipped version.

Constants

CURRENT_VERSION

The version number every fresh save is written as. Bump in lockstep with adding a new versions/vN.rs and routing it in load_from_str.

Functions

load_from_str

Best-effort load from a JSON string. Falls back to a default state if the input is malformed at any layer of the chain. The result is always passed through GameState::migrate_runtime so ephemeral #[serde(skip)] fields (flash vecs, count-up tweens, etc.) are seeded.

save_to_string

Serialize the live state to its on-disk JSON form. The version field is whatever the caller has on state — GameState::default() and the migration chain both stamp CURRENT_VERSION, so the only way to write a wrong version is to mutate state.version by hand, which nothing does.