Engagement

Engagement defines how people, agents, and devices participate in a world without tying world behavior to one renderer or input method.

Semantic sequence

Actor
  perceives an affordance
  expresses an intent
  the world authorizes an action
  the host performs effects
  the actor receives feedback
  and optionally a receipt

Actors

An actor is a participant with a session-scoped identity and declared roles. An actor MAY represent:

• a person;
• a guest browser session;
• an authenticated account;
• an autonomous or supervised agent;
• a device;
• a group or delegated role.

Identity proof and account systems are profiles. Core engagement requires only an opaque actor identifier and the authority attached to it.

Affordances

An affordance advertises possible engagement:

{:affordance/id "affordance:garden/open-studio"
 :affordance/intents #{:open}
 :affordance/target "entity:studio-console"
 :affordance/bounds
 {:shape :sphere
  :space/id "main"
  :position [2 1 -4]
  :radius 0.5}
 :affordance/presentations
 #{:world/marker :ui/label :audio/cue}
 :affordance/action :studio/open}

Bounds and presentations are optional projections. The semantic action remains available to non-visual clients when policy permits.

Intents

An intent describes what an actor asks to do: enter, leave, inspect, open, close, activate, take, place, move, speak, follow, invite, publish, sign, purchase, or another namespaced operation.

Pointer clicks, touch, gaze, keyboard, voice, controller input, accessibility switches, and agent commands can all emit the same intent.

Actions

An action is a world-authorized state transition. Hara evaluates the intent against world state, actor authority, rules, and required capabilities. An action can emit zero or more effects and semantic events.

Feedback

Feedback is the actor-facing consequence of an action. It MAY be spatial, visual, audible, haptic, textual, or programmatic. A conforming world SHOULD provide a non-spatial fallback for essential actions.

Portals

A portal is a typed transition to another world, space, application surface, or session. A portal descriptor states the target, transition intent, identity continuity, state handoff, and capability renegotiation policy. Authority never crosses a portal implicitly.

Receipts

A receipt records an action when auditability matters:

{:receipt/id "receipt:01J..."
 :receipt/action "action:publish-4"
 :receipt/actor "actor:alice"
 :receipt/world "world:greenways/splat-garden"
 :receipt/time "2026-08-05T00:00:00Z"
 :receipt/digest "sha256-..."
 :receipt/signatures []}

Signing and chain anchoring are optional profiles. Unsigned local receipts are still useful for deterministic replay and debugging.