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/core/store/serialize.ts

@@ -12,6 +12,7 @@ import {
   nodeDef,
   STATE,
 } from '../graph';
+import { isParticleNodeDef } from '../particles/nodes';
 import { isShaderNodeDef } from '../shader/nodes';
 import type { Asset, TextureFrame } from '../model/Asset';
 import { isAssetType } from '../model/AssetTypes';
@@ -48,6 +49,7 @@ import {
   type StructFieldDef,
   variableDef,
 } from '../properties/PropertySchema';
+import { particleParamDefs } from '../properties/particles';
 import { SHADER_KEY, shaderParamDefs } from '../properties/shaders';
 
 /**
@@ -64,6 +66,7 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
   const rawProps = new Map<string, Record<string, unknown>>();
   const shaderGraphs = new Map<string, Graph>();
   const shaderRows = new Map<string, PropertyDef[]>();
+  const particleGraphs = new Map<string, Graph>();
   for (const a of rawAssets) {
     if (typeof a.id !== 'string' || !a.id || !isAssetType(a.type)) continue;
     rawProps.set(a.id, asRecord(a.props));
@@ -71,6 +74,12 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
       const vars = normalizeVariables(a.variables);
       variables.set(a.id, vars);
       schemas.set(a.id, [...COMMON_PROPS, ...vars]);
+    } else if (a.type === 'particles') {
+      // A source's rows end with its own graph's parameters, so the graph is needed before the
+      // overrides of the objects placed from it can be coerced.
+      const graph = normalizeGraph(a.graph, isParticleNodeDef);
+      particleGraphs.set(a.id, graph);
+      schemas.set(a.id, [...schemaFor('particles'), ...particleParamDefs(graph)]);
     } else {
       if (a.type === 'shader') {
         const graph = normalizeGraph(a.graph, isShaderNodeDef);
@@ -115,6 +124,8 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
       assets.push({ id, type, name, props, graph: normalizeGraph(a.graph, (def) => def.type === STATE) });
     } else if (type === 'shader') {
       assets.push({ id, type, name, props, graph: shaderGraphs.get(id) ?? createEmptyGraph() });
+    } else if (type === 'particles') {
+      assets.push({ id, type, name, props, graph: particleGraphs.get(id) ?? createEmptyGraph() });
     } else if (type === 'texture') {
       assets.push({ id, type, name, props, ...normalizeTexture(a, takenIds) });
     } else if (type === 'font') {