Real-time games: fixed-rate ticks and deterministic lockstep

GAOS supports fixed-tick real-time games with the same deterministic reducer used for turn-based and WEGO play. The SDK owns ticks, lockstep input ordering, rollback/resimulation, replay verification, and the session kernel. The product owns its scheduler and wall clock, sockets or WebRTC transport, signaling, interpolation, rendering, late-join flow, and latency policy.

That makes fixed-tick action and strategy games first-class Game-as-a-Benchmark environments rather than limiting the category to turn-based tasks.

import {
  createTickRate,
  tickAtElapsedMilliseconds,
  type TickReducer,
} from '@yugao-gaos/gaos-sdk/engine';

const rate = createTickRate(30);
// rate.millisecondsPerTick === 33.333...

const currentTick = tickAtElapsedMilliseconds(elapsedMs, rate);
for (; simulatedTick < currentTick; simulatedTick++) {
  state = reducer.advance(state, inputsFor(simulatedTick));
}

The host owns elapsedMs, scheduling, catch-up limits, rendering, and interpolation. The reducer sees only explicit tick-numbered inputs.

Reducer guidance

A tick with no submitted intents should take a near-free empty-input path: advance only scheduled systems whose explicit boundary is crossed. Reducers must be deterministic, but they need not be persistently immutable. At high frequency, in-place mutation with copy-on-write rollback deltas is legitimate. The solver is the exception: it explores sibling actions from one parent, so its adapter must snapshot or otherwise protect the parent state.

Keep reducer state free of wall-clock reads. Hosts translate deadlines, elapsed time, disconnects, and substitutions into ordinary tick-numbered inputs. Mint ids from deterministic counters or seeded streams, and avoid cross-engine transcendental floating-point operations unless the result is quantized.

Seat lifecycle

Disconnect, rejoin, and human/bot substitution are host events injected as ordinary inputs. A product may switch a disconnected seat to a behavior-tree driver, make it auto-wait, or call eliminateSeat and apply a declared policy to its entities. Reconnection changes the seat's driver back; ownership and authoritative state never move. Record the chosen transition with its tick or tick so rollback and replay reach the same result.

Sparse transcripts and rollback

TranscriptAction.tick records input deltas. Empty ticks may be omitted; recheckTranscript and resimulate infer gaps and call a product applyEmptyTick callback when supplied. Lockstep inputs are canonically ordered by tick, lexical seat id, then authored action order.

Peers can compare stateDigest values at agreed ticks to locate the first desync. The product must provide canonical serialization for maps, sets, and presentation-only fields. Pure peer-to-peer lockstep replicates full state: per-seat views prevent accidental disclosure but not a modified client's maphack.

For open-information games, products may use optimistic P2P plus a dispute verifier: exchange signed canonical inputs and digests, accept matching results, and send a divergent transcript to an authoritative server for deterministic replay. This provides integrity, fault detection, and arbitration. It does not provide confidentiality: a client that passively reads replicated secrets can still submit a legal action and produce the same digest as every honest peer.

Competitive hidden-information games therefore keep authoritative secret state in a server-side session resolver (for example, one Durable Object per match) and distribute only viewFor(state, seat) observations. The resolver collects canonical intents, applies the reducer, retains the full replay record, and sends each client its redacted result. P2P input exchange or digest comparison may still be used around that authority, but no untrusted client receives another seat's hand, deck order, or unrevealed fog state.

Agent decision cadence

AgentEnvironment.step() advances exactly one simulation tick. Products own the policy for requesting a new decision less often, holding an input, or repeating an action. Every applied tick, observation, and reward is retained in transcript version 1.3.

MultiAgentEnvironment applies a canonical simultaneous batch through TickReducer.advance. Each seat receives only viewFor(state, seat) and its legal actions. Missing policies or deadline misses contribute a legal wait. One shared transcript records the redacted per-seat views, canonical intent batches, and per-seat rewards/outcomes.

The hosted HTTP tick protocol shares the participation and canonical collection model, but it is not a 60 Hz transport. Realtime products bring WebRTC, relay, or socket transport and use the reducer, lockstep inputs, rollback, and digest helpers directly.