Cargo workspace:

• core/ (sav_core) — the whole pipeline, pure Rust: chunked zlib decompression, save parsing into a compact SaveStore (the decompressed buffer is retained; strings are zero-copy u32 ranges into it), and mapdata/ — the map-payload builder, save index, and the six detail queries the frontend uses (describeInstance, findItemLocations, building/vehicle/train info, selection inventory). Static game data (game_data/generated/{docs,world}/*.json, game_data/curated/*.json, the item-icon manifest) is embedded at compile time, so building requires the game data extracted first (see the root README).
• wasm/ (sav_wasm) — the wasm-bindgen boundary. SaveSession::load parses a .sav from bytes and builds payload + index; the query methods return JSON strings. Loaded by map/static/map/worker.js inside a Web Worker (built with wasm-pack --target no-modules by tools/build_site.py).

• Single-threaded on wasm; the parallel feature enables rayon chunk decompression for native builds (same chunk order, identical output bytes).
• Progress reporting is a plain FnMut(phase, current, total) driven synchronously from inside the parse/build; the worker forwards it to the page as postMessage events.
• mapdata/ is a behavioral port of the original Python map/sav_map_data.py (see git history / the main branch). It was landed collector-by-collector behind a bit-exact differential gate against the Python reference (order-strict JSON comparison, float.hex() equality), which is why the code deliberately reproduces Python quirks: dict insertion-order semantics (IndexMap; last-value-wins/first-position-kept), CPython's own math.hypot algorithm (jsonval::py_hypot), banker's rounding (py_round), exact Python repr(float) (display.rs), rem_euclid for Python %, absence-vs-null-vs-0 distinctions. Do not "simplify" these without understanding what they mirror.
• Decompressed-save size cap is wasm32-only: StrRef/DataRef and the store's span/offset fields use usize offsets, which is u32 on wasm32 (the browser build — a 4GB address space it can't exceed anyway) and 64-bit on native (the desktop app), so native has no cap. The guard in decompress.rs is #[cfg(target_pointer_width = "32")].

cargo test -p sav_core            # unit tests (fixtures generated from CPython)
py tools/build_site.py            # wasm build + site assembly into dist/