0.7.7

A lifecycle release. <tosi-b3d> now distinguishes being moved from being removed, which fixes an engine leak and a scene-corruption bug that were the same root cause seen from two ends.

Fixed

• A MOVE no longer costs a scene (#58, and the real cause of the black sky in #51). connectedCallback built an Engine and a Scene unconditionally, so re-parenting built a SECOND pair — and disposing the first deleted its materials' shader programs, after which the surviving scene rendered black while every uniform read correct and isReady() returned true.

  Re-parenting fires disconnectedCallback then connectedCallback in the same task, and it need not touch the element at all: moving any ancestor does it to every descendant. Ensemble hit this with a <tosi-b3d> inside their own shadow root, re-parented by the doc system — their MutationObserver recorded no tosi-b3d add or remove at all while two scenes were being built.

  Teardown is now deferred by a task, so a reconnect cancels it and reuses the engine.

• A genuine removal disposes the Engine and Scene. Teardown released the XR helper, the quality subscription and the debug timers, but never the engine — so every removed scene left a live render loop turning over a detached canvas forever. A WebGL context is not just memory: Chrome caps them near 16 per page and force-loses the oldest, so an SPA that visits scene pages works for a dozen route changes and then a scene that was fine goes black.

  This is also the better explanation for doc-site slowdown after visiting several demos, and possibly for headset degradation — N abandoned render loops compete for frame time, which retained VRAM does not.

• whenReady no longer drops queued callbacks. Asking for the scene and having it torn down before it was ready lost the callback silently — no call, no error, nothing to observe. It now survives and fires against the next scene.

• addSceneListener is no longer handed dead meshes. Past additions outlived their scene, so after a rebuild a late subscriber received nodes belonging to the disposed one.

Added

• b3d.whenDisposed(cb) → unsubscribe — the other half of whenReady, and the half that did not exist. Fires on a genuine disposal, not on a move. Durable across rebuilds, so register once.

  Use it for anything holding a reference into the scene that a child's sceneDispose() does not cover — a timer closing over a mesh, a material cache, an observer on a node. After disposal those point at a dead scene, and Babylon's failure mode there is a black material that still reports isReady(): silent, not loud.

  One rule governs both hooks: subscriptions are durable, scene state is not.