gamedev-the-steward/docs/SIMULATION_STATE_SCHEMA.md

# The Steward — Simulation State Schema

## Current contract

`SimulationStateRecord` is the versioned JSON boundary for the current
simulation. The current world schema is v10 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;
- scene-independent animal identity, position, hunger, feeding history,
  reservation, and availability state;
- pantry contents, carried NPC inventory, the ordered economic event stream,
  and its next stable event ID;
- directed relationship records with familiarity, trust, and the stable event
  ID that last changed trust;
- per-NPC known-event records that reference objective event history without
  copying it, including first-acquisition method, acquisition tick, and
  historical communicator provenance;
- opportunity records with stable type/status, interested NPC, trigger event,
  target storage/resource/amount, exact later resolution event identity, or a
  deterministic invalidation reason and close tick.

The top-level identity is:

```json
{
  "schema": "the_steward.simulation",
  "schema_version": 10
}
```

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, directed relationship/cause
round-tripping, divergent known-event state, communicated provenance, and
deterministic retention boundaries, and rejection of unsupported schemas.
Active, resolved, and invalidated opportunity round-tripping, contradictory
target state, invalid resource sources, and cross-record event references are
covered too.

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 and
wood into the stable `village_pantry` and `village_woodpile` records. 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).

EconomicEventRecord v2 adds the authoritative world position captured when the
fact is recorded. Nested v1 events migrate with a zero-vector fallback; old
saves already encode their stable location IDs, and migrated knowledge is not
recomputed spatially.

SimulationStateRecord v4 moves social authority into top-level directed
`RelationshipStateRecord` entries. Each record contains `observer_id`,
`subject_id`, familiarity, trust, and `last_trust_cause_event_id` (`-1` when no
event has changed trust). Parsing requires unique ordered pairs, existing NPC
IDs, bounded relationship values, and a real event for every non-empty cause
ID.
The relationship system serializes records in stable observer/subject order so
they participate in deterministic checksums.

World schema v3 migrates its NPC-local familiarity pairs into directed
relationships with neutral trust. Nested NPC schema v4 removes that obsolete
duplicate field; v3 NPC records remain accepted only through the explicit
migration. World schemas v1–v2 also derive the graph from any legacy
familiarity data (or initialize it empty) after their storage/event migrations.

SimulationStateRecord v5 adds top-level `KnownEventStateRecord` entries keyed
by `knower_id` and `event_id`. The objective `EconomicEventRecord` remains the
single completed fact; knowledge records only state which NPC knows it. Parsing
requires unique NPC/event pairs and valid references to both an existing NPC
and an event in the same record. A relationship's causal event must also be
known by that relationship's observer and, for the current trust contract, be
a food deposit performed by the relationship subject.

World schema v4 migrates relationship causes into known-event records. The old
schema used village-wide awareness, so this preserves the implied known fact
without falsely inventing spatial witness provenance.

SimulationStateRecord v6 / KnownEventStateRecord v2 adds immutable
first-acquisition provenance: `performed`, `witnessed`, `communicated`, or
`legacy`. Communicated records also retain the stable NPC ID of the direct
speaker. New direct facts are created only at event-record time from the actor
and nearby NPC positions; historical events are never re-evaluated against
current positions. A co-located shared-activity encounter can add one
communicated reference to the original fact without appending or replaying the
event.

World schema v5 migrates actor-owned knowledge to `performed`; non-actor
knowledge becomes `legacy` because v5 may contain either a proximity witness or
an older implied relationship fact. Parsing never invents that missing
provenance. At runtime, communication requires a distinct source who currently
knows the event through `performed` or `witnessed` acquisition. Persisted
records validate that direct-method snapshot even after the source forgets.
This enforces the current one-hop boundary and makes validation independent of
array ordering.

SimulationStateRecord v7 / KnownEventStateRecord v3 adds `acquired_tick` and a
snapshot of the direct speaker's acquisition method. Direct facts use the
objective event tick; newly communicated facts use the conversation tick. The
speaker snapshot keeps historical provenance valid even if the speaker later
forgets their own copy, while runtime communication still requires a currently
known performed/witnessed fact and remains one-hop.

World schema v6 migrates direct acquisition to the objective event tick.
Communicated and ambiguous legacy facts receive a fresh retention lease at the
saved simulation tick because their exact acquisition time was not previously
stored. The v6 source record supplies the persisted direct-method snapshot.

Importance is intentionally derived rather than duplicated: a fact is
`lasting` while it is the current trust cause for one of that knower's directed
relationships; every other fact is `recent`. Current causal facts are protected
so relationship state remains explainable. Each NPC keeps at most three recent
facts, and recent facts at least one simulated day old are removed at the next
deterministic daily-sized review. The objective event stream is never pruned by
this rule.

SimulationStateRecord v8 adds the top-level `opportunities` array and
`simulation.next_opportunity_id`. The first nested `OpportunityStateRecord`
schema stores `opportunity_id`, `opportunity_type`, `status`, `created_tick`,
`trigger_event_id`, `interested_npc_id`, `target_id`, `resource_id`,
`target_amount`, `resolution_event_id`, and `resolved_tick`. World schemas
v1–v7 migrate explicitly to an empty opportunity list with next ID zero.

SimulationStateRecord v9 preserves world-v8 opportunity history and upgrades
the nested record to `OpportunityStateRecord` v2. The nested schema adds
`closed_tick` and `invalidation_reason`, accepts `supply_missing_wood`, and adds
the stable `invalidated` status. Nested opportunity v1 records normalize their
resolved tick into the close tick and remain valid pantry history. Economic
event schema v3 adds normalized `action_id` and `required_amount` fields;
nested v1/v2 events receive empty/zero defaults, while a new `task_blocked`
event requires its stable action, source storage, resource, and positive
requirement contract.

SimulationStateRecord v10 adds the top-level `animals` array and the first
`AnimalStateRecord` schema. Each animal record stores its stable animal and
species IDs, display name, authoritative world position, hunger,
`last_fed_tick`, reservation owner, and enabled/player/NPC feeding flags.
World schema v9 preserves opportunity history while migrating to an empty
animal list.

Current-schema parsing requires unique animal IDs that do not collide with
resource or storage IDs. An animal reservation must belong to an existing NPC
whose active feed task targets that exact animal. Every `animal_fed` event
must name the pantry as its source, an existing animal as its destination,
food as its item, the exact feed action cost, and a valid NPC actor or the
player sentinel. The latest matching feed event tick must agree with the
animal's `last_fed_tick`.

The bounded opportunity family accepts at most one open record globally.
Opportunity, trigger-event, and resolution-event IDs are unique and the next
ID must remain above restored history. Referenced NPCs, storage, resources, and
events must exist. A `restock_empty_pantry` trigger is a positive NPC food
withdrawal from `village_pantry` to that actor's matching inventory; an open
record additionally requires the pantry to remain below its one-food target
and its interested NPC to have acquired that fact no later than creation. A
`supply_missing_wood` trigger is the performer's known patrol or study
`task_blocked` fact against `village_woodpile` with a one-wood requirement; an
open record additionally requires a living interested performer and the
woodpile below target.

Resolution references an exact later matching NPC inventory-to-storage deposit
or player `resource_extracted` event from an existing player-usable matching
resource into the target storage, with matching resolved and closed ticks.
Resolved history does not require the storage still to contain the resource
because later use is valid. Invalidation has no resolution event and requires a
stable close tick and is currently valid only for `supply_missing_wood`.
`interested_died` must agree with the restored NPC's death state; the runtime
creates `evidence_stale` at the one-day unresolved boundary.

While a need is open, its interested villager's trigger evidence is treated as
lasting during deterministic memory maintenance. Resolution or invalidation
releases that fact back to the normal bounded-retention rules; neither deletes
objective event or opportunity history.

`OpportunityHelperResult` and `OpportunityPlayerResponseResult` are deliberately
absent from this schema. The helper result is re-derived from the open
opportunity plus current NPC knowledge, directed relationship, inventory,
action-definition, storage-capacity, and finite-resource records. The player
result additionally requires no capable helper and derives its ordinary gather
action, real destination, and source count from current enabled player-usable
finite resources. Save/restore regressions require the same applicable route
result and an unchanged checksum before and after querying.

When an idle derived helper chooses the reported supply action, only the
existing NPC task, task-state, target, travel, and reservation fields serialize.
The helper result remains absent: restore retains any in-progress ordinary task
and independently re-derives current capability from restored facts.

Active-need communication adds no schema fields. It persists through the
existing `KnownEventStateRecord` event, listener, source NPC, direct source
method, and acquisition-tick fields. Communication and player-response HUD
animations are transient and are cleared rather than replayed after restore.

## Resource authority

`SimulationManager` owns `ResourceStateRecord` instances independently of the
scene tree. Amount, reservation, enabled state, action/resource identity,
yield, usage permissions, and discovery metadata 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 v3 adds `safety_risk`, `comfort_distance`, and
`discovery_priority` so unloaded resources keep the same target-selection
meaning after save/restore. Nested v1 and v2 resource records are migrated
explicitly. Current-schema parsing also canonicalizes numeric, boolean, and ID
variants so a freshly registered finite source retains a byte-stable checksum
after a JSON round trip.

## Animal authority

`AnimalCareSystem` owns `AnimalStateRecord` instances independently of the
scene tree and advances their hunger in stable-ID order. `AnimalNode` binds a
loaded presentation and interaction point to that authority; the simulation
position remains canonical while the node is loaded or absent.

Animals are not `ResourceNode` instances and are not inserted into the
resource discovery grid. The first bounded slice uses a deterministic linear
loaded-animal query. NPC and player feeding resolve through the same atomic
care operation: reserve or select the exact animal, withdraw one real food
from `village_pantry`, reduce that animal's hunger, and append one exact
`animal_fed` fact. Failed withdrawal changes neither animal nor history.

The persistent hungry/content presentation derives from authoritative hunger.
The short feed response is transient and is reset rather than serialized or
replayed after restore.

## 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 from any historical world schema other than the explicitly
  supported v1–v9 layouts;
- player inventory or player relationship records;
- broader relationship dimensions, line-of-sight/hearing evidence,
  continuous or personalized memory decay, reinforcement, false beliefs, or
  multi-hop rumours;
- generalized opportunity/quest definitions, acceptance, rewards, assignment,
  dialogue, or player-facing quest-log state;
- persistence for the player transform or presentation-only scene state.

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