Pixijs Scene Container

`Container` is the general-purpose node of the PixiJS v8 scene graph. It holds children and applies transforms, alpha, tint, and blend mode to its whole subtree. Every display object you make will either be a `Container` you're building a branch on, or a leaf (`Sprite`, `Graphics`, `Text`, `Mesh`) that you nest inside one.

Assumes familiarity with `pixijs-scene-core-concepts`.

## Quick Start

```ts
const group = new Container({
  label: "hero-group",
  x: 200,
  y: 150,
  sortableChildren: true,
});

const body = new Sprite(await Assets.load("body.png"));
const head = new Sprite(await Assets.load("head.png"));
head.position.set(0, -40);
head.zIndex = 1;

group.addChild(body, head);
group.pivot.set(group.width / 2, group.height / 2);
group.scale.set(1.5);

app.stage.addChild(group);
```

**Related skills:** `pixijs-scene-core-concepts` (scene graph mental model, masking, layers, render groups), `pixijs-scene-sprite` / `pixijs-scene-graphics` / `pixijs-scene-text` / `pixijs-scene-mesh` (leaf objects that go inside containers), `pixijs-events` (`eventMode`, hit testing), `pixijs-math` (Matrix, toGlobal/toLocal detail), `pixijs-performance` (`cacheAsTexture`, culling, render groups).

## Core Patterns

### Constructor options

```ts
const container = new Container({
  label: "world",
  x: 100,
  y: 50,
  scale: 2,
  rotation: Math.PI / 4,
  alpha: 0.8,
  visible: true,
  tint: 0xffaa00,
  blendMode: "add",
  sortableChildren: true,
  isRenderGroup: true,
  origin: { x: 0, y: 0 },
  boundsArea: new Rectangle(0, 0, 1920, 1080),
});
```

All `Container` options (`position`, `scale`, `tint`, `label`, `filters`, `zIndex`, etc.) are also valid here — see `skills/pixijs-scene-core-concepts/references/constructor-options.md`.

The `Container` constructor uses `assignWithIgnore` to bulk-copy every field in the options object onto the instance except `children`, `parent`, and `effects`. Any public property of `Container` is a valid constructor option: `cullable`, `cullArea`, `mask`, `filterArea`, `eventMode`, `hitArea`, and so on. The options block above groups the most common ones; see the shared reference above for the full list.

`isRenderGroup: true` promotes the container to its own render group so its transforms are applied on the GPU rather than recomputed per-child on the CPU. Use it on stable sub-trees (large static worlds, UI layers). Don't overuse; most scenes don't need explicit render groups and too many hurts performance. Profile before promoting. See `pixijs-scene-core-concepts/references/scene-management.md`.

`sortableChildren: true` causes children to be re-sorted by `zIndex` at the next render. See `zIndex` below.

`origin` is a first-class v8 transform helper: an `ObservablePoint` that acts as a rotation/scale center **without** moving the container. Where `pivot` shifts the projection of the local origin in parent space (so changing it displaces the object), `origin` leaves position alone and simply rotates/scales around the specified local point. Accepts `PointData`, a single number (applied to both axes), or can be set live via `container.origin.set(x, y)`. Setting both `pivot` and `origin` on the same container produces compounding behavior and is discouraged; pick one.

`boundsArea` forces `getBounds()` to return a fixed rectangle instead of recursiv