A particle is a function of its age, not a thing that is stepped (#73)

The asset type `particles` is placeable and carries a graph at the same time —
`behavior` was the blueprint. Because a continuous emitter gives birth to particle n
at time n/rate, the whole field is a function of the clock rather than of the frames:
no ring-buffer bookkeeping, exact time jumps, reproducibility as a measurable property.

compile.ts follows compileShader's frame but emits JS closures into a Float64Array
instead of GLSL, and without eval; a node with two consumers is evaluated once.
Drawing is one Pixi ParticleContainer per source, so one draw call.

Collision, wind and braking in flight are out for good — that is the price of the
formula model, not an omission.

The tab count goes from nine to ten, which is exactly the case #84 was built for one
day earlier: at 1280 px the row no longer holds every tab, so guard 14b now asks for
hidden.length > 0 instead of === 0.

src/editor/Editor.ts

@@ -21,6 +21,7 @@ import { HierarchyPanel } from './panels/HierarchyPanel';
 import { Toolbar } from './panels/Toolbar';
 import { type PlayHost, PlaySession, type WorldSnapshot } from './PlaySession';
 import { ProjectSession } from './ProjectSession';
+import { ParticlesEditor } from './particles/ParticlesEditor';
 import { ShaderEditor } from './shader/ShaderEditor';
 import { StateMachineEditor } from './statemachine/StateMachineEditor';
 import { installShortcuts } from './shortcuts';
@@ -29,7 +30,16 @@ import { TextureEditor } from './texture/TextureEditor';
 import { installFileImport } from './fileImport';
 
 export type CentreTab =
-  'scene' | 'graph' | 'statemachine' | 'shader' | 'game' | 'texture' | 'animation' | 'container' | 'list';
+  | 'scene'
+  | 'graph'
+  | 'statemachine'
+  | 'shader'
+  | 'particles'
+  | 'game'
+  | 'texture'
+  | 'animation'
+  | 'container'
+  | 'list';
 
 const TAB_ORDER = [
   'scene',
@@ -37,6 +47,7 @@ const TAB_ORDER = [
   'graph',
   'statemachine',
   'shader',
+  'particles',
   'texture',
   'animation',
   'container',
@@ -49,6 +60,7 @@ const TAB_LABELS: Record<CentreTab, string> = {
   graph: 'Behavior',
   statemachine: 'State machine',
   shader: 'Shader',
+  particles: 'Particles',
   texture: 'Texture',
   animation: 'Animation',
   container: 'Container',
@@ -61,6 +73,7 @@ const TAB_OF_ASSET: Partial<Record<AssetType, CentreTab>> = {
   behavior: 'graph',
   statemachine: 'statemachine',
   shader: 'shader',
+  particles: 'particles',
   texture: 'texture',
   animation: 'animation',
   container: 'container',
@@ -87,6 +100,7 @@ export class Editor implements PlayHost {
   readonly graphEditor: GraphEditor;
   readonly stateMachineEditor: StateMachineEditor;
   readonly shaderEditor: ShaderEditor;
+  readonly particlesEditor: ParticlesEditor;
   readonly textureEditor: TextureEditor;
   readonly animationEditor: AnimationEditor;
   readonly containerEditor: ContainerEditor;
@@ -129,6 +143,7 @@ export class Editor implements PlayHost {
     this.graphEditor = new GraphEditor(state);
     this.stateMachineEditor = new StateMachineEditor(state);
     this.shaderEditor = new ShaderEditor(state);
+    this.particlesEditor = new ParticlesEditor(state);
     this.textureEditor = new TextureEditor(state);
     this.animationEditor = new AnimationEditor(state);
     this.containerEditor = new ContainerEditor(state);
@@ -175,6 +190,7 @@ export class Editor implements PlayHost {
       graph: this.graphEditor,
       statemachine: this.stateMachineEditor,
       shader: this.shaderEditor,
+      particles: this.particlesEditor,
       texture: this.textureEditor,
       animation: this.animationEditor,
       container: this.containerEditor,
@@ -233,7 +249,9 @@ export class Editor implements PlayHost {
           ? 'statemachine'
           : state.selectedShaderId
             ? 'shader'
-            : 'graph';
+            : state.selectedParticlesId
+              ? 'particles'
+              : 'graph';
         if (this.tab !== tab) this.showTab(tab);
       }
       if (s?.kind === 'frame' && this.tab !== 'texture') this.showTab('texture');
@@ -305,6 +323,7 @@ export class Editor implements PlayHost {
     this.gameView.animate();
     this.console.refresh();
     if (this.tab === 'animation') this.animationEditor.tick(dt);
+    if (this.tab === 'particles') this.particlesEditor.tick();
   }
 
   private measureFps(dt: number): void {