# The Steward — Simulation State Schema

## Current contract

`SimulationStateRecord` is the versioned JSON boundary for the current
simulation. The current world schema is v3 and captures:

- simulation seed, tick interval, tick count, clock remainder, and elapsed
  clock ticks;
- every NPC's identity, needs, attributes, task lifecycle, target, position,
  starvation state, and decision RNG stream;
- village resource counters;
- controlled per-NPC wander RNG streams;
- scene-independent resource state plus the definition facts needed while its
  ResourceNode is unloaded.
- pantry contents, carried NPC inventory, the ordered economic event stream,
  and its next stable event ID.

The top-level identity is:

```json
{
  "schema": "the_steward.simulation",
  "schema_version": 3
}
```

Unknown schema versions and structurally incomplete records are rejected. Add
an explicit migration function before accepting a future version; never
silently reinterpret old data as the newest layout.

NPC action and profession references are serialized as stable strings and
restored as `StringName`. Records referencing unknown executable actions or
professions are rejected against the validated definition registry. See
[the simulation definitions](SIMULATION_DEFINITIONS.md).

## Deterministic continuation

RNG seeds and internal states are encoded as decimal strings. They are signed
64-bit values and cannot safely pass through every JSON number implementation
without precision loss. Converting them to ordinary JSON numbers caused a
restored simulation to retain the same visible state while silently changing
its future random sequence.

`tests/simulation_state_serialization_test.gd` protects this contract by:

1. running a fixed-seed scenario for 48 ticks without interruption;
2. running the same scenario for 24 ticks;
3. serializing and restoring into a fresh manager;
4. running the remaining 24 ticks;
5. requiring the complete final-state checksums to match.

It also verifies clock remainder, resource amount/reservation/enabled
round-tripping, presentation unload/rebind, and rejection of unsupported
schemas.

NPCStateRecord v2 adds the resolved travel destination and whether it is
active. Nested v1 NPC records migrate explicitly with no invented active
destination. This allows a reloaded visual to resume travel without changing
target selection or deterministic RNG state.

NPCStateRecord v3 adds carried inventory. SimulationStateRecord v2 adds
StorageStateRecord entries; world-schema v1 migrates legacy village food into
the stable `village_pantry` record. Parsed storage values are canonicalized so
save/restore continuation retains byte-stable checksums.

SimulationStateRecord v3 adds ordered `EconomicEventRecord` entries and
`next_event_id`. World schemas v1 and v2 migrate explicitly to an empty event
stream. Event records use stable source/destination/item IDs, reject invalid or
duplicate IDs, and preserve deterministic ordering across save/restore. See
[the economic event stream](ECONOMIC_EVENTS.md).

## Resource authority

`SimulationManager` owns `ResourceStateRecord` instances independently of the
scene tree. Amount, reservation, enabled state, action/resource identity,
yield, and usage permissions remain available and serializable while no
ResourceNode is loaded.

ResourceNode binds to a record by stable ID and provides presentation,
interaction transforms, and active-world discoverability. Unloading a node does
not delete its record. Loading another node with the same stable ID rebinds to
the existing record and cannot overwrite its amount or reservation with scene
defaults.

ResourceStateRecord v2 adds the definition facts needed while unloaded. Nested
v1 resource records are migrated explicitly and hydrate their missing
definition from a matching presentation node when one becomes available.

## Local quicksave boundary

`SaveSlotStore` writes the existing versioned JSON record to
`user://saves/quicksave.json`. It validates the serialized record before
replacement, limits file size, restricts slot names, preserves the previous
file during replacement, and can recover that backup if replacement is
interrupted. Loading parses and validates the complete record before mutating
the simulation.

In `main.tscn`, F5 saves and F9 loads this slot. Restoration rebuilds active NPC
visuals from authoritative state.

## Deliberately out of scope

This phase does not yet provide:

- a save-slot menu, metadata, thumbnails, autosaves, or multiple profiles;
- migrations older than the explicitly supported world schemas v1 and v2;
- player inventory, relationship, schedule, or social-memory records;
- persistence for the player transform or presentation-only scene state.

Those features should build on this boundary rather than inventing parallel
serialization paths.
