editor/wiki/architecture/plugin-authoring.md

Plugin authoring

Public contract for external node packs that extend the Pascal editor.

Applies to: anything that ships a Plugin for the editor to load.

This page documents the contract, not a loader implementation. The host call site (discoverPlugins()) is in place; turning it into a real network loader is a separate plan.

Plugin shape

A plugin is a JS object exporting one symbol — the manifest:

import type { Plugin } from '@pascal-app/core'

export const myPlugin: Plugin = {
  id: 'acme:furniture-pack',
  apiVersion: 1,
  nodes: [
    couchDefinition,
    armchairDefinition,
    // ...
  ],
}

Field	Required	Notes
id	yes	Globally unique. Use vendor:pack-name to avoid collisions. The host treats it as opaque.
apiVersion	yes	Currently 1. The host throws on mismatch — bumping breaks plugins, intentionally.
nodes	optional	Array of AnyNodeDefinition.

The standalone pascalorg/plugin-trees repository is the worked example. Clone it as a starting point.

The same shape powers the built-in pascal:core plugin in @pascal-app/nodes — there's no "internal" plugin format. Whatever works for built-ins works for third parties.

What a NodeDefinition can contribute

A plugin's nodes array is the only meaningful contribution point in v1. Each entry is a NodeDefinition<S extends ZodObject> that the registry stamps with kind, schemaVersion, schema, and any combination of:

• defaults — initial field values for new instances.
• capabilities — selectable / duplicable / deletable / surfaces / relations flags consumed by the framework.
• parametrics — auto-derived inspector UI shape (fields + optional customPanel escape hatch).
• renderer — custom 3D React component (GLB, drei, TSL — opt-out of def.geometry).
• system — per-frame work (animation, dirty-cascade, runtime state).
• geometry — pure (node, ctx) => Object3D for the generic <GeometrySystem>.
• floorplan — pure (node, ctx) => FloorplanGeometry for the 2D layer.
• floorplanAffordances / floorplanMoveTarget — 2D drag handlers.
• tool / affordanceTools — 3D placement + move tools (lazy components).
• presentation — palette / sidebar metadata (label, icon, paletteSection, etc.).
• mcp — MCP tool descriptions for AI consumers.
• relations / computeLevelData — sibling lookups + level-batch precompute.

See node-definitions.md for the three-checkbox composition model that ties these together.

Importing host packages

A plugin imports from the published @pascal-app/* packages — same surface the built-ins use, peer-dependency-style:

// Schemas, types, registry types
import {
  type AnyNode,
  type NodeDefinition,
  type Plugin,
  z, // re-exported from zod for schema authoring
} from '@pascal-app/core'

// Viewer-side primitives (lazy: only inside renderers / systems)
import { useNodeEvents, NodeRenderer } from '@pascal-app/viewer'

// Editor-side primitives (lazy: only inside `tool` / `affordanceTools`)
import { useDragAction, EDITOR_LAYER } from '@pascal-app/editor'

The packages are peer dependencies, not normal dependencies — the host app owns the version. A plugin that pins its own copy of @pascal-app/core would create two registries and silently fail. (npm peer-dep resolution catches this at install time.)

Lifecycle

graph TD
  Boot["App boot"] --> LoadBuiltin["loadPlugin(builtinPlugin)"]
  LoadBuiltin --> Discover["await discoverPlugins()"]
  Discover --> LoadEach["for each plugin: await loadPlugin(plugin)"]
  LoadEach --> Ready["Registry frozen for the session"]

loadPlugin is add-only for v1. Hot-removing a kind would require tearing down every mounted instance in the scene — out of scope. Plugins are loaded once at boot.

registerNode throws on duplicate kind, so two plugins shipping a kind: 'couch' is a startup-time error, not a silent overwrite.

Discovery: setPluginDiscovery

The host calls discoverPlugins() after the built-in plugin loads. The default implementation returns []. Apps that ship external plugins replace it before the bootstrap module evaluates:

// In app boot, BEFORE `import './pascal-bootstrap'`
import { setPluginDiscovery } from '@pascal-app/core'
import { myPlugin } from '@acme/furniture-pack'

setPluginDiscovery(async () => {
  // Static import: bundled into the app.
  return [myPlugin]

  // Or fetch a manifest, dynamic-import each entry, etc.
  // const manifest = await fetch('/plugins.json').then(r => r.json())
  // return Promise.all(manifest.map(m => import(m.url).then(mod => mod.default)))
})

setPluginDiscovery is global. Calling it twice silently overwrites — order with the bootstrap import matters.

Host panels and project installation

The core Plugin manifest remains renderer-agnostic. A plugin that also ships editor UI exports an EditorHostPanel separately:

import type { EditorHostPanel } from '@pascal-app/editor'

export const myHostPanel: EditorHostPanel = {
  id: 'acme:furniture-pack:catalog',
  pluginId: 'acme:furniture-pack',
  label: 'Furniture pack',
  description: 'A curated furniture catalog.',
  creator: {
    name: 'Acme',
    url: 'https://acme.example',
  },
  pluginUrl: 'https://github.com/acme/pascal-furniture-pack',
  icon: { kind: 'iconify', name: 'lucide:armchair' },
  component: () => import('./catalog-panel'),
}

The host registers that panel with registerEditorHostPanel. Registered plugins appear in the Plugins sidebar, while the scene graph's installedPlugins: string[] controls which plugin panels appear in that project's icon rail. defaultInstalled: true opts a first-party plugin into legacy and newly created projects; Nature uses this today.

Install/uninstall is a project-level visibility operation. Plugin code and node definitions stay loaded for the browser session because loadPlugin is add-only, but an uninstalled plugin's panel, placement UI, renderers, systems, and floor-plan output are disabled. Existing plugin nodes remain serialized in the scene graph and become visible again when the plugin is reinstalled; uninstall never deletes project data.

creator and pluginUrl are optional manager metadata. Selecting a plugin in the Plugins sidebar opens its detail page, where the host shows this metadata and the project install/uninstall control.

Host panels mount lazily inside an error boundary. Use host CSS variables, keep CSS scoped to the plugin, and do not write global styles.

Versioning

apiVersion: 1 covers the surface above. The host bumps the major when it removes or changes the shape of an existing field. New optional fields don't bump. The plan is to keep additions backwards-compatible as long as possible — the bump is the escape hatch, not the default.

A plugin's own data versioning is schemaVersion on each NodeDefinition. The host doesn't migrate; the plugin's migrate(node, fromVersion) (future) handles its own legacy persisted nodes.

What's not a plugin contribution (yet)

• Materials — there's no plugin.materials slot. Use createMaterial from @pascal-app/viewer inside your def.renderer / def.system.
• Floor-plan primitives — the FloorplanGeometry union is host-owned. To draw something the union can't express, fall back to def.renderer and render through a different 2D mount (or open an issue).
• Panels / sidebar UI in the core manifest — host-specific. Export an EditorHostPanel separately for hosts that use @pascal-app/editor.
• Stores — plugins create their own Zustand stores; they don't extend useScene, useEditor, or useViewer. Host stores are not part of the v1 plugin surface.
• Routes / pages — plugins are visualisation + interaction code, not full app surfaces. Hosting a settings page belongs to the app.

The boundary stays narrow on purpose so the contract is shippable. Each "not yet" item is a plan, not a "never."

Testing your plugin

@pascal-app/nodes is the built-in reference implementation, and pascalorg/plugin-trees is the standalone example. To test locally:

1. Build your plugin as a normal npm package with @pascal-app/* as peerDependencies.
2. In a host app that consumes your built-ins (apps/editor is the easiest target), wire setPluginDiscovery to return your plugin.
3. The dev-mode [pascal:registry] console log shows the loaded plugin id + node count — that's the verification anchor.

The host's own parity test (packages/nodes/src/index.test.ts) asserts every AnyNode discriminator has a registered kind. Plugin-contributed kinds don't participate in that test (they're not in AnyNode); add an equivalent test on your own side if you maintain a hand-typed union elsewhere.