Fighting Game · Guides & deep dives

V2 Rollback Isolation

The side-channel carries non-authoritative hints for presentation, coaching, and post-frame recommendations:

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Rollback simulation consumes only deterministic inputs and match-start payload bytes. AI Director output, Psyche tendency profiles, Iris commentary, and any Oshun-sourced data arrive through a behavior-hint side-channel that rollback does not read, hash, predict, rewind, or replay as simulation authority.

Behavior-Hint Channel#

The side-channel carries non-authoritative hints for presentation, coaching, and post-frame recommendations:

  • AI Director pacing suggestions for camera, encounter dressing, tutorial prompts, and post-round presentation.
  • Psyche tendency profile summaries for out-of-band coaching and opponent-read overlays.
  • Iris commentary intents, translated captions, and highlight narration.
  • Oshun-sourced recommendations from event bus, gRPC, dashboards, or companion apps.

Determinism Rules#

  • Rollback frame simulation ignores behavior hints completely.
  • Behavior hints are never included in rollback snapshots, deterministic frame hashes, hit resolution, input prediction, correction, or replay verification.
  • A hint can affect gameplay only if it is baked into the deterministic match-start payload before frame 0, byte-identical on every peer, and recorded into the replay container.
  • If an Oshun service is unavailable, rollback simulation must produce identical frame hashes.
  • Presentation systems can drop, delay, or reorder hints without changing match outcome.

Message Envelope#

Every behavior hint uses this envelope before reaching Unreal:

json
{
  "channel": "v2.behavior_hint",
  "matchId": "match_01HYV2",
  "frameObserved": 1842,
  "producer": "iris.commentary",
  "determinism": "ignored_by_rollback",
  "expiresAtFrame": 2040,
  "payloadHash": "sha256:9b861...",
  "payload": {
    "intent": "commentary.reversal_callout"
  }
}

Required fields:

  • channel is always v2.behavior_hint.
  • frameObserved is the latest resolved frame the producer may reference; it is not an input to simulation.
  • producer identifies the source domain, such as ai-director, psyche.tendency, iris.commentary, or oshun.recommendation.
  • determinism is always ignored_by_rollback.
  • expiresAtFrame prevents late hints from being applied to presentation after their window is gone.
  • payloadHash is for audit and cache de-duplication only.

Unreal Routing#

  • V2Services receives behavior hints from Oshun services.
  • V2AdaptiveAI may consume live @psyche/behavior-prediction hints only in non-rollback modes. Rollback-with-CPU modes receive only a match-start snapshot.
  • V2Telemetry, V2Audio, V2Cinematics, V2UI, and non-authoritative director systems may subscribe.
  • V2Combat, V2Gameplay, V2Input, and V2Netcode rollback do not subscribe and do not include the side-channel headers.
  • Replays may store behavior hints as optional presentation metadata, but replay verification ignores that metadata and hashes only deterministic streams.

Test Contract#

Golden replay tests must pass with behavior hints present, absent, delayed, and reordered. The expected deterministic frame hashes are identical in all four cases.

V2/ue/Tools/check-rollback-determinism.py runs in CI with a self-test fixture. It fails if V2Netcode rollback frame code references V2AdaptiveAI, @psyche/behavior-prediction, V2Services, gRPC, or HTTP service reads, and it also fails if V2AdaptiveAI contains live Psyche RPC/client reads instead of match-start snapshot consumption.