Presence

@* Any part with the state-attribute contract. No KeepMounted needed for exits. *@
<NaviusCollapsiblePanel class="motion-pop">
    ...
</NaviusCollapsiblePanel>

Preset classes

Add one class. Every preset fades (so exits always clear cleanly) and enters to the element's natural state. Enters use a calmer spring; every exit uses the snappy spring, because exits should get out of the way faster than enters arrive.

Each preset also has an insert-only twin, .motion-enter-* (for example .motion-enter-fade-up), built on @starting-style. Those animate once when the element enters the DOM and need no state attributes at all; delay them with --navius-motion-delay.

The state contract

The presence classes read the same discrete attributes every Navius primitive part already emits. Nothing else couples the two: drop the class on the part and the primitive's own deferred-unmount timing drives the exit.

Splat helpers

For zero-wrapper usage, Motion returns attribute dictionaries to splat with @attributes. Blazor's duplicate-attribute rule is last wins, so splat these instead of a literal class, or merge manually.

The runtime path

When you need interruption handling (rapid open/close on an overlay), use the WAAPI tier. MotionPrograms.Presence bakes a preset's enter and exit springs in C#; CreatePresenceMotionAsync attaches an observer that runs them from a live computed snapshot, so an interrupted enter hands over to the exit continuously. It cooperates with the presence machine's deferred unmount through getAnimations() with no extra coupling.

@inject IJSRuntime JS

var interop = new MotionJsInterop(JS);
var options = MotionPrograms.Presence(MotionPresets.Get(Preset.Pop));
// Override either phase's spring if you like:
// MotionPrograms.Presence(MotionPresets.Get(Preset.Pop), exitSpring: Spring.Smooth);
_presence = await interop.CreatePresenceMotionAsync(_element, options);

// Later: await _presence.DisposeAsync();

MotionJsInterop

Bridge to navius-motion.js. CreatePresenceMotionAsync returns a PresenceMotion; dispose it to disconnect the observer and cancel its animations.

PresenceMotionOptions

Enter plays when data-starting-style appears or is removed; exit when data-ending-style appears. Build it from a preset with MotionPrograms.Presence.

MotionPhase

One presence phase: the keyframes plus the baked timing to play them with.