RUDPFramework/openspec/specs/client-prediction-cadence/spec.md

client-prediction-cadence Specification

Purpose

Define that client forward prediction accumulation uses an explicit cadence derived from the server authoritative movement cadence, not Time.fixedDeltaTime, ensuring prediction timing aligns with authoritative timing in reconciliation-sensitive paths.

Requirements

Requirement: Forward prediction accumulation uses authoritative cadence

The controlled-client forward prediction path SHALL accumulate pending input duration using the server authoritative movement cadence as the unit of accumulation, not Time.fixedDeltaTime or other render-loop-derived values. This ensures SimulatedDurationSeconds reflects server-time and remains coherent with the server's 50ms step cadence.

Scenario: Accumulation uses server cadence regardless of FixedUpdate interval

• WHEN the client FixedUpdate runs at a 20ms interval
• THEN AccumulateLatest adds kServerSimulationStepSeconds (50ms) to the pending input duration
• THEN the accumulated SimulatedDurationSeconds reflects server-time, not real elapsed time

Scenario: Accumulation cadence is decoupled from frame rate

• WHEN FixedUpdate runs at a non-standard interval due to platform variation or frame drops
• THEN the accumulation unit remains kServerSimulationStepSeconds
• THEN prediction timing does not drift relative to the server's authoritative cadence

Requirement: Forward prediction and replay use the same cadence source

The controlled-client prediction system SHALL use the same cadence source for both forward accumulation and replay substepping, ensuring that SimulatedDurationSeconds consumed during replay matches the cadence used during forward prediction.

Scenario: Forward accumulated duration matches replay substep size

• WHEN the client accumulates pending input for 100ms of server-time
• THEN the replay path consumes the same 100ms in 50ms substeps
• THEN the forward accumulated duration and replay duration are derived from the same cadence constant