Rune scripting

Rune scripts. Every subsystem declares its bindings once, against a seam with no language in it, so a second language cost the engine nothing.

What landed

• The seam. balaur_script is the neutral contract: a binding is a name, typed values and a function. A backend implements ScriptHost against it. Physics, input, render, audio and UI declare their bindings there and know no language.
• Rune. balaur_script_rune is the host, picked by language in project.toml. One object per node, pub fn update(this, dt), and what a script writes to this is what the host reads next frame. Rune reads like Rust without types.
• The node API, once. Twenty-seven node operations are one list of neutral functions taking the node first. A backend adds only its call sugar; a third language would cost the sugar, not the operations.
• Exported properties. pub fn exports() returns defaults; the scene overrides only what it changes; the inspector lists them per node.
• Component handles. Each component a node carries is a field on the node, and the field's methods are the driving module's functions with the node filled in. get(), set(table), has() and remove() on all of them.

pub fn exports() {
    #{ speed: 2.0 }
}

pub fn fixed_update(this, dt) {
    // physics2d::apply_impulse(this.node, ...), spelled from the node
    this.node.body2d.apply_impulse(this.speed * dt, 0.0);
}

Luau was the first host and Rune the second; a few days on, Rune is the only one. Scripting has the model.