refactor(api)!: v0.15 Welle 1 — System.update(delta), serializer per-app, dead barrel removed

BREAKING: unifies the System.update protocol across all managers and removes a
dead internal rendering barrel.

3a — System.update(delta: Time): void across all 5 app systems. InputManager
  update(): this -> update(_delta: Time): void (fluent return removed);
  InteractionManager + AudioManager gain the param. Tween/RenderingContext were
  already conform. 0 external call-sites broke. The param is `_delta` (unused but
  required by the System contract; lint:strict forbids unused non-_ args, the
  spec's "lint allows it" assumption was empirically wrong).

3b — registerSerializer + Prefab.from/instantiate gain an optional `registry`
  param (per-app serialization; default = global). New @internal
  _resetDefaultSerializers() + SerializationRegistry.clear() close a cross-suite
  global-registry leak (serialization.test.ts:273); afterEach reset + 2 new tests.

3d — deleted dead internal barrel src/rendering/index.ts (0 static imports;
  migrated its one dynamic test import to #rendering/public). Documented the
  abstract-vs-concrete renderer boundary in renderer-sdk.ts + custom-renderers guide.

api-mdx regenerated (audio/input/interaction-manager, prefab). 3395 tests pass.

Author: Exoridus

site/src/content/api/audio-manager.mdx

@@ -9,7 +9,7 @@ memberCount: 18
 tier: "stable"
 sections: ["Import", "Constructors", "Methods", "Properties", "Events", "Source"]
 sourcePath: "src/audio/AudioManager.ts"
-sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/audio/AudioManager.ts#L24"
+sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/audio/AudioManager.ts#L25"
 ---
 ## Import
 
@@ -41,7 +41,7 @@ AudioManager.muteOnHidden is enabled.
 - `play(source: Playable, options?: PlayOptions): Voice`
 - `registerBus(bus: AudioBus): this`
 - `unregisterBus(bus: AudioBus): this`
-- `update(): void`
+- `update(_delta: Time): void`
 
 ## Properties
 
@@ -58,4 +58,4 @@ AudioManager.muteOnHidden is enabled.
 
 ## Source
 
-[src/audio/AudioManager.ts](https://github.com/Exoridus/ExoJS/blob/main/src/audio/AudioManager.ts#L24)
+[src/audio/AudioManager.ts](https://github.com/Exoridus/ExoJS/blob/main/src/audio/AudioManager.ts#L25)

site/src/content/api/input-manager.mdx

@@ -9,7 +9,7 @@ memberCount: 38
 tier: "stable"
 sections: ["Import", "Constructors", "Methods", "Properties", "Events", "Source"]
 sourcePath: "src/input/InputManager.ts"
-sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/input/InputManager.ts#L60"
+sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/input/InputManager.ts#L61"
 ---
 ## Import
 
@@ -44,7 +44,7 @@ automatically — you do not instantiate this class yourself.
 - `onStart(channel: InputChannel | readonly InputChannel[], callback: object, options?: InputBindingOptions): InputBinding`
 - `onStop(channel: InputChannel | readonly InputChannel[], callback: object, options?: InputBindingOptions): InputBinding`
 - `onTrigger(channel: InputChannel | readonly InputChannel[], callback: object, options?: InputBindingOptions): InputBinding`
-- `update(): this`
+- `update(_delta: Time): void`
 
 ## Properties
 
@@ -83,4 +83,4 @@ automatically — you do not instantiate this class yourself.
 
 ## Source
 
-[src/input/InputManager.ts](https://github.com/Exoridus/ExoJS/blob/main/src/input/InputManager.ts#L60)
+[src/input/InputManager.ts](https://github.com/Exoridus/ExoJS/blob/main/src/input/InputManager.ts#L61)

site/src/content/api/interaction-manager.mdx

@@ -9,7 +9,7 @@ memberCount: 7
 tier: "stable"
 sections: ["Import", "Constructors", "Methods", "Source"]
 sourcePath: "src/input/InteractionManager.ts"
-sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/input/InteractionManager.ts#L70"
+sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/input/InteractionManager.ts#L71"
 ---
 ## Import
 
@@ -42,8 +42,8 @@ this class yourself.
 - `getHoveredNode(pointerId?: number): RenderNode | null`
 - `popInputCapture(): void`
 - `pushInputCapture(root: RenderNode): void`
-- `update(): void`
+- `update(_delta: Time): void`
 
 ## Source
 
-[src/input/InteractionManager.ts](https://github.com/Exoridus/ExoJS/blob/main/src/input/InteractionManager.ts#L70)
+[src/input/InteractionManager.ts](https://github.com/Exoridus/ExoJS/blob/main/src/input/InteractionManager.ts#L71)

site/src/content/api/prefab.mdx

@@ -9,7 +9,7 @@ memberCount: 4
 tier: "stable"
 sections: ["Import", "Methods", "Source"]
 sourcePath: "src/core/serialization/Prefab.ts"
-sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/core/serialization/Prefab.ts#L26"
+sourceUrl: "https://github.com/Exoridus/ExoJS/blob/main/src/core/serialization/Prefab.ts#L27"
 ---
 ## Import
 
@@ -35,11 +35,11 @@ for (let i = 0; i \< 10; i++) \{
 
 ## Methods
 
-- `instantiate(loader: Loader | null): SceneNode`
+- `instantiate(loader: Loader | null, registry?: SerializationRegistry): SceneNode`
 - `toJSON(): SerializedNode`
-- `from(node: SceneNode, loader: Loader | null): Prefab`
+- `from(node: SceneNode, loader: Loader | null, registry?: SerializationRegistry): Prefab`
 - `fromJSON(descriptor: SerializedNode): Prefab`
 
 ## Source
 
-[src/core/serialization/Prefab.ts](https://github.com/Exoridus/ExoJS/blob/main/src/core/serialization/Prefab.ts#L26)
+[src/core/serialization/Prefab.ts](https://github.com/Exoridus/ExoJS/blob/main/src/core/serialization/Prefab.ts#L27)

site/src/content/guide/debugging/custom-renderers.mdx

@@ -129,6 +129,8 @@ Direct backend access is deliberately unabstracted — you are writing raw WebGP
 
 ExoJS resolves a renderer for each drawable type through the `RendererRegistry` (available from `@codexo/exojs/renderer-sdk`). You can register a custom renderer for an existing drawable type via `backend.rendererRegistry.registerRenderer(drawableConstructor, renderer)`. A renderer implements `connect(backend)`, `disconnect()`, `render(drawable)`, and `flush()` — these map to GPU resource acquisition, release, per-drawable recording, and batch submission respectively.
 
+In practice you build a custom renderer by extending one of the **abstract** base renderers from `@codexo/exojs/renderer-sdk` — `AbstractWebGl2Renderer` / `AbstractWebGl2BatchedRenderer` (WebGL2) or `AbstractWebGpuRenderer` (WebGPU) — which is exactly how the `@codexo/exojs-particles` and `@codexo/exojs-tilemap` packages build theirs. The engine's built-in *concrete* renderers (e.g. `WebGl2SpriteRenderer`) are internal: coupled to internal sprite/mesh data paths and intentionally not part of the SDK surface, so don't subclass them directly.
+
 Registering a custom renderer is an advanced extension point. For most custom rendering needs — procedural geometry between draws, a single custom shape that doesn't fit `Mesh` — `CallbackRenderPass` is the simpler and more intentional path.
 
 ## When to use which

src/audio/AudioManager.ts

@@ -1,5 +1,6 @@
 import { Signal } from '#core/Signal';
 import type { System } from '#core/System';
+import type { Time } from '#core/Time';
 
 import { getAudioContext, isAudioContextReady, onAudioContextReady } from './audio-context';
 import { AudioBus } from './AudioBus';
@@ -132,8 +133,8 @@ export class AudioManager implements System {
     });
   }
 
-  /** Called once per frame from Application.update(). */
-  public update(): void {
+  /** Called once per frame from Application.update(). The frame delta is unused here (hence `_delta`); present for {@link System} contract compliance. */
+  public update(_delta: Time): void {
     this.listener._tick();
     // Tick spatial voices and prune ended ones.
     for (const voice of this._spatial) {

src/core/serialization/Prefab.ts

@@ -1,6 +1,7 @@
 import type { SceneNode } from '#core/SceneNode';
 import type { Loader } from '#resources/Loader';
 
+import type { SerializationRegistry } from './SerializationRegistry';
 import { deserializeTree, serializeTree } from './serialize';
 import type { SerializedNode } from './types';
 
@@ -28,10 +29,12 @@ export class Prefab {
 
   /**
    * Capture `node`'s subtree as a prefab. Pass the {@link Loader} so texture and
-   * other asset references resolve to their source keys.
+   * other asset references resolve to their source keys. Pass `app.serializers`
+   * as `registry` to resolve app-scoped (extension) serializers; defaults to the
+   * global registry.
    */
-  public static from(node: SceneNode, loader: Loader | null = null): Prefab {
-    return new Prefab(serializeTree(node, loader));
+  public static from(node: SceneNode, loader: Loader | null = null, registry?: SerializationRegistry): Prefab {
+    return new Prefab(serializeTree(node, loader, registry));
   }
 
   /**
@@ -46,9 +49,11 @@ export class Prefab {
   /**
    * Instantiate a fresh, independent copy of the captured subtree. Referenced
    * assets must be pre-loaded into `loader`. Call repeatedly for many instances.
+   * Pass `app.serializers` as `registry` to resolve app-scoped (extension)
+   * serializers; defaults to the global registry.
    */
-  public instantiate(loader: Loader | null = null): SceneNode {
-    return deserializeTree(this._descriptor, loader);
+  public instantiate(loader: Loader | null = null, registry?: SerializationRegistry): SceneNode {
+    return deserializeTree(this._descriptor, loader, registry);
   }
 
   /** The underlying JSON descriptor (JSON-serialisable). Treat as read-only. The standard `JSON.stringify(prefab)` hook. */

src/core/serialization/SerializationRegistry.ts

@@ -93,6 +93,18 @@ export class SerializationRegistry {
   public hasType(typeName: string): boolean {
     return this._byName.has(typeName) || (this._fallback?.hasType(typeName) ?? false);
   }
+
+  /**
+   * Remove every own registration (both the name and constructor maps). The
+   * fallback chain is left untouched. Test infrastructure only — used to reset
+   * the {@link defaultSerializationRegistry} between suites so process-wide
+   * registrations do not leak across them.
+   * @internal
+   */
+  public clear(): void {
+    this._byName.clear();
+    this._byCtor.destroy();
+  }
 }
 
 /**
@@ -103,7 +115,10 @@ export class SerializationRegistry {
 export const defaultSerializationRegistry = new SerializationRegistry();
 
 /**
- * Register a custom {@link NodeSerializer} on the {@link defaultSerializationRegistry}.
+ * Register a custom {@link NodeSerializer}. Defaults to the
+ * {@link defaultSerializationRegistry}; pass `app.serializers` to register the
+ * type only for that {@link Application} (it stays isolated from other apps and
+ * from the global registry, resolving through the fallback chain).
  *
  * Use this to make your own {@link SceneNode} subclasses serializable. Delegate
  * to a base type's behaviour by composing with the framework helpers, or
@@ -116,6 +131,11 @@ export const defaultSerializationRegistry = new SerializationRegistry();
  * });
  * ```
  */
-export function registerSerializer<T extends SceneNode>(typeName: string, ctor: SceneNodeConstructor<T>, serializer: NodeSerializer<T>): void {
-  defaultSerializationRegistry.register(typeName, ctor, serializer);
+export function registerSerializer<T extends SceneNode>(
+  typeName: string,
+  ctor: SceneNodeConstructor<T>,
+  serializer: NodeSerializer<T>,
+  registry: SerializationRegistry = defaultSerializationRegistry,
+): void {
+  registry.register(typeName, ctor, serializer);
 }

src/core/serialization/serialize.ts

@@ -26,6 +26,23 @@ function ensureCoreSerializers(): void {
   registerCoreSerializers(defaultSerializationRegistry);
 }
 
+/**
+ * Reset the process-wide serialization state so test suites do not leak
+ * registrations into one another. Clears both module-level states: the
+ * {@link defaultSerializationRegistry} **and** the `_coreRegistered` latch. Both
+ * are mandatory — clearing the registry alone would leave the latch `true`, so
+ * the core serializers would never re-register and later round-trips would fail
+ * with spurious "No serializer registered" errors.
+ *
+ * Not exported from the public barrel; import via the direct module path in
+ * tests.
+ * @internal — For unit tests only.
+ */
+export function _resetDefaultSerializers(): void {
+  _coreRegistered = false;
+  defaultSerializationRegistry.clear();
+}
+
 function createSerializeContext(loader: Loader | null, registry: SerializationRegistry): SerializeContext {
   const ctx: SerializeContext = {
     version: SERIALIZATION_VERSION,

src/input/InputManager.ts

@@ -1,6 +1,7 @@
 import type { Application } from '#core/Application';
 import { Signal } from '#core/Signal';
 import type { System } from '#core/System';
+import type { Time } from '#core/Time';
 import { stopEvent } from '#core/utils';
 import { Flags } from '#math/Flags';
 import { getDistance } from '#math/utils';
@@ -333,7 +334,7 @@ export class InputManager implements System {
    * the channel buffer, fires the corresponding Signals, then evaluates
    * each registered binding.
    */
-  public update(): this {
+  public update(_delta: Time): void {
     this.updateGamepads();
 
     for (const binding of this.bindings) {
@@ -343,8 +344,6 @@ export class InputManager implements System {
     if (this.flags.value !== InputManagerFlag.None) {
       this.updateEvents();
     }
-
-    return this;
   }
 
   public destroy(): void {