arora-behavior

The behavior interpreters of Arora: the executors the runtime ticks each step.

Mind the two meanings of "behavior":

• A behavior (the noun) is an authored, editable representation of what a device should do — a behavior tree, a node graph — produced in a visual editor (Studio, the Vizij Workspace) and shipped as data.
• A BehaviorInterpreter is the runtime-level executor that runs one of those. It is the thing the runtime actually ticks.

A BehaviorInterpreter advances one step at a time — tick(&mut BehaviorContext) — and reports whether it is Running or Done. The context hands it the shared data store (read inputs, write intent) and the module-call bridge. The behavior tree is one interpreter (arora-behavior-tree's BehaviorTreeInterpreter); a node graph is another. The runtime queues Box<dyn BehaviorInterpreter> and ticks them without knowing which is which.

Implement BehaviorInterpreter to add a new kind of executor — a new authored-behavior representation the runtime can run. Hand-implementing it to hard-code one particular behavior in Rust is a corner case, not the promoted path: author a behavior in an editor and let an interpreter run it.

How it works, with diagrams: docs/interpreter-workflow.md walks the interpreter lifecycle — load, time update, ticks, graph updates, and "keeps ticking" — grounded in the source. See a concrete interpreter in arora-behavior-tree and the whole device loop in arora.

Built-in keys: timing is data, not an argument

The runtime keeps time out of the tick signature. Before it ticks any behavior, it publishes the frame's clock into the shared store under two reserved built-in keys a behavior can rely on:

A behavior that paces itself — an animation module, a graph time node — reads them from ctx.store like any other slot, so timing composes as ordinary data rather than a special tick parameter. They live under the reserved arora/ namespace (built_in::is_built_in) and stay local to the device: the runtime never forwards them out over the bridge. The names and the predicate are in the built_in module.

Part of the device runtime interfaces, with arora-hal and arora-bridge.