RUDPFramework/openspec/specs/client-authoritative-player-state/spec.md

client-authoritative-player-state Specification

Purpose

Define how the Unity client owns, applies, and exposes authoritative PlayerState snapshots for local and remote players.

Requirements

Requirement: Client keeps one owned authoritative player-state snapshot per player

The client SHALL keep one explicit owned authoritative PlayerState snapshot for each known player instead of spreading authoritative field ownership across unrelated presentation components. The owned snapshot MUST be the source of truth for authoritative position, rotation, hp, and optional velocity on the client.

Scenario: Incoming authoritative state replaces the owned snapshot

• WHEN the client accepts a newer PlayerState for a player
• THEN the latest accepted packet becomes that player's owned authoritative snapshot on the client
• THEN presentation and diagnostics read authoritative position, rotation, hp, and optional velocity from that owned snapshot

Requirement: Local player reconciliation applies the full authoritative state by tick

The controlled client SHALL continue reconciling local prediction from authoritative PlayerState snapshots while keeping authoritative HP and optional velocity synchronized with the owned player-state snapshot. Reconciliation MUST use the acknowledged movement-input tick defined by the sync strategy, and the visible controlled-player transform MUST keep authoritative gameplay truth separate from short-lived visual correction state. Replay of pending inputs during reconciliation MUST use fixed-step substeps matching the server authoritative movement cadence, producing identical trajectory to live prediction for the same input sequence. Small divergence after replay MUST converge through explicit bounded correction state, while large divergence or failed convergence MUST still snap immediately to authoritative position and rotation.

Scenario: Local authoritative state corrects predicted presentation

• WHEN the controlled player accepts an authoritative PlayerState whose acknowledged movement-input tick is N
• THEN local reconciliation prunes or replays predicted movement using tick N according to the sync strategy
• THEN the replay uses fixed-step substeps matching the server authoritative movement cadence
• THEN the controlled player's authoritative gameplay state updates immediately to the accepted position, rotation, HP, and optional velocity
• THEN the local player's visible transform may temporarily differ only through bounded visual correction state that converges back to the authoritative baseline

Scenario: Consecutive small corrections replace or fold into active visual correction

• WHEN the controlled player accepts a newer authoritative PlayerState while a bounded visual correction is still active and the new residual error remains inside the configured bounded-correction limits
• THEN the client updates the active visual correction state according to the sync strategy instead of preserving stale correction targets indefinitely
• THEN the controlled player's authoritative gameplay state still reflects only the newest accepted PlayerState

Scenario: Large local divergence bypasses bounded correction

• WHEN the controlled player accepts an authoritative PlayerState and the remaining transform error exceeds the configured snap threshold or the active bounded correction can no longer converge within its budget
• THEN the controlled player's visible transform snaps immediately to authoritative position and rotation
• THEN any temporary visual correction state is cleared before later local prediction resumes from that authoritative baseline

Scenario: Replay produces identical trajectory to live prediction

• WHEN the controlled player replays pending inputs after accepting authoritative PlayerState
• THEN the replay applies inputs in fixed-duration substeps equal to the server authoritative movement cadence
• THEN the final predicted pose equals what live FixedUpdate prediction would produce for the same input sequence
• THEN the result is stable across multiple replays of the same input sequence

Requirement: Remote players apply authoritative state without inventing gameplay truth

Remote player presentation SHALL consume the accepted authoritative player-state snapshot owned by the client and MUST NOT invent HP or final gameplay state locally. Remote movement presentation MUST smooth authoritative position and rotation through a small buffered snapshot interpolation path instead of applying only the latest snapshot directly. Stale remote PlayerState packets that are older than the latest accepted authoritative tick for that player MUST NOT overwrite the owned snapshot or enter the interpolation buffer.

Scenario: Remote authoritative state updates interpolation input and rejects stale packets

• WHEN a remote player receives a newer authoritative PlayerState
• THEN the client's owned snapshot for that remote player updates to the newer authoritative state
• THEN remote presentation adds that accepted authoritative sample to the interpolation buffer for position and rotation smoothing
• THEN an older later-arriving PlayerState for that remote player does not overwrite the newer authoritative snapshot or affect interpolation

Requirement: Authoritative HP and state changes are observable during MVP development

The client SHALL expose authoritative HP or comparable authoritative state information through lightweight UI or diagnostics so developers can observe server-truth changes during MVP playtests.

Scenario: Development UI reflects authoritative HP

• WHEN the client accepts a PlayerState whose authoritative HP differs from the previously accepted snapshot
• THEN the relevant UI or diagnostics update to show the new authoritative HP value
• THEN the displayed value comes from authoritative PlayerState data rather than speculative local gameplay logic

Requirement: Client-owned authoritative player presentation can consume authoritative combat-result deltas

The client-owned authoritative player presentation model SHALL accept authoritative combat-result updates in addition to full PlayerState snapshots. Applying an authoritative CombatEvent for a player MUST be able to adjust the client-owned HP, death state, or related combat presentation truth for that player until a newer authoritative PlayerState snapshot refreshes the full state.

Scenario: Authoritative combat event updates owned player presentation state

• WHEN the client applies a CombatEvent that targets or otherwise affects a known player
• THEN that player's owned authoritative presentation state updates to reflect the authoritative combat result
• THEN a later accepted PlayerState snapshot remains allowed to refresh the full authoritative state for that player