workspace-app-composition

name	workspace-app-composition
description	How a workspace-backed app under `apps/*` is composed: the isomorphic doc factory (`create<App>`), the environment factories (`open<App>Browser` / `open<App>Extension` / tauri), the `#platform/*` build-time platform DI for multi-platform (Tauri) apps, the `session` singleton, daemon/script placement under per-project `workspaces/<app>/`, and the file layout itself. Use when creating a new app, naming or placing the iso/browser/extension factory, wiring `#platform/*` subpath imports for a Tauri seam, choosing between auth-gated (Shape A) vs module-singleton (Shape B), placing the session singleton, or registering daemon/script bindings.
metadata	{"author":"epicenter","version":"5.0"}

Workspace App Layout

A workspace app is composed in layers: a pure isomorphic doc factory, one or more environment factories that bind it to a runtime (browser, Chrome extension, Tauri), a single side-effectful session singleton, and (for the two multi-platform apps) a build-time platform DI seam. Daemon and script bindings do not live in the app package at all; they live per-project under workspaces/<app>/ and are registered through epicenter.config.ts.

Two shipped shapes; pick by whether the app gates UI on signed-in identity.

Shape A: auth-gated SvelteKit web apps (honeycrisp, vocab, fuji). The app is not a running thing until identity exists, so a session singleton owns the workspace lifecycle and UI lives under (signed-in) routes.

Shape B: module-level singleton apps (opensidian, tab-manager, whispering). A module singleton blocks on auth/session readiness and exports a constructed handle.

File Layout

Two layouts ship today. Single-platform apps keep the composition files flat at the package root; the two apps with a src-tauri/ directory (fuji, whispering) nest the same files under src/lib/workspace/ and add a src/lib/platform/ seam.

Flat root (honeycrisp, opensidian, vocab):

apps/<app>/
|- <app>.ts                  iso schema + create<App>() factory   (package "." export)
|- <app>.browser.ts          browser env factory open<App>Browser()
|- <app>.test.ts             tests
|- mount.ts                  mount factory <app>()                (package "./mount" export)
`- src/lib/
   |- session.ts             the session singleton (NOT session.svelte.ts)
   `- platform/auth/         auth client construction

Nested under src/lib/workspace/ (fuji, whispering; both have src-tauri/):

apps/<app>/
|- package.json              "imports" map declares the #platform/* seams
`- src/lib/
   |- workspace/
   |  |- index.ts            iso schema + create<App>() factory   (package "." export)
   |  |- browser.ts          browser env factory open<App>Browser()
   |  |- index.test.ts       tests
   |  `- mount.ts            mount factory <app>()                (package "./mount" export)
   |- session.ts             the session singleton
   `- platform/              #platform/* impls (X.browser.ts / X.tauri.ts) + types.ts contract

Package exports follow the file's actual owner. Every app exports the iso factory as . and the mount factory as ./mount:

// honeycrisp / vocab (flat root)
"exports": {
  ".": "./honeycrisp.ts",
  "./mount": "./mount.ts"
}

// fuji (nested): the export points straight at the implementation; there is
// no root re-export wrapper.
"exports": {
  ".": "./src/lib/workspace/index.ts",
  "./mount": "./src/lib/workspace/mount.ts"
}

Opensidian additionally exports "./browser": "./opensidian.browser.ts"; the others do not export their browser factory. That asymmetry is honest, opensidian has a consumer that needs the bare browser factory and the others do not. Do not add a ./browser export to the rest for symmetry's sake.

Layers

Layer	File	Shape	Job	Returns
Iso factory	<app>.ts / workspace/index.ts	A + B	create<App>(): pure doc construction	workspace (ydoc, tables, kv, actions)
Browser factory	<app>.browser.ts / workspace/browser.ts	A + B	open<App>Browser({ signedIn, nodeId }): bind to browser persistence + sync	iso bundle plus IndexedDB/local storage, collaboration
Extension / tauri factory	<app>.extension.ts etc.	B	bind to chrome.storage / Tauri APIs	iso bundle plus runtime resources
Mount factory	mount.ts / workspace/mount.ts	A + B	<app>(opts?): calls <app>Workspace.mount({ runtime: nodeMountRuntime(), ... }) and returns the Mount a project's epicenter.config.ts default-exports	Mount (node persistence, materializers)
Session singleton	src/lib/session.ts	A	createSession({ ... }): owns workspace lifecycle, side effects	session, session.require
Auth	src/lib/platform/auth/ (or #platform/auth)	A	auth client construction	auth

The iso factory, browser/extension factory, and mount factory are pure construction surfaces. Side effects (auth subscriptions, HMR disposal, persisted state, network) live only in the session singleton (src/lib/session.ts).

Iso Factory

create<App>() builds the document and returns the workspace. It is the package . export and the wire contract for sync: every browser, mount, and test consumer imports it, and forking a table column shape breaks sync compatibility with peers running the canonical schema.

export function createHoneycrisp() {
	const workspace = createWorkspace({
		id: HONEYCRISP_ID,
		tables: { /* ... */ },
		kv: {},
	});
	return defineWorkspace({
		...workspace,
		actions: defineActions({
			// Pure workspace actions that depend only on tables.
		}),
	});
}

Rules:

• Keep the iso factory free of node:*, bun:*, chrome.*, Tauri APIs, y-indexeddb, BroadcastChannel, and runtime singletons. It must type-check and run isomorphically.
• Put pure actions inline as actions: defineActions({ ... }) in the returned workspace when they depend only on tables.
• Keep env-bound actions in the env factory when they need filesystem, SQLite, shell, or browser persistence. Extract only when the runtime action set is shared or owns a boundary that would be harder to read inline.

Browser Factory

open<App>Browser({ signedIn, nodeId }) calls the iso factory, then attaches local persistence and collaboration.

export function openHoneycrispBrowser({
	signedIn,
	nodeId,
}: {
	signedIn: SignedIn;
	nodeId: NodeId;
}) {
	const workspace = createHoneycrisp();
	const idb = attachLocalStorage(workspace.ydoc, {
		server: signedIn.server,
		ownerId: signedIn.ownerId,
	});
	const collaboration = openCollaboration(workspace.ydoc, { /* ... */ });
	return { ...workspace, idb, collaboration };
}

Session Singleton (Shape A)

The singleton lives in src/lib/session.ts (a plain .ts module, not session.svelte.ts). createSession owns the workspace lifecycle; the app re-exports session.require under an app-specific name.

import { createSession } from '@epicenter/svelte/auth';
import { auth } from '#platform/auth'; // fuji; flat-root apps import from $lib/platform/auth

export const session = createSession({ /* auth + build */ });
export const requireHoneycrisp = session.require;

This is the only home for the singleton. Do not add a client.ts or a second singleton site.

Platform DI: the #platform/* seam

Multi-platform apps (the two with src-tauri/: fuji, whispering) select browser-vs-Tauri implementations at BUILD time via Node-standard #platform/* subpath imports. This is the canonical mechanism. It replaced the old resolve.extensions / moduleSuffixes suffix trick (see "Why not suffixes" below).

1. Declare the seam in package.json "imports". Each seam maps a bare specifier to a Tauri impl and a default (browser) impl:

"imports": {
  "#platform/tauri": {
    "tauri": "./src/lib/platform/tauri.tauri.ts",
    "default": "./src/lib/platform/tauri.browser.ts"
  }
}

2. Consume the bare specifier, with NO platform branch at the call site:

import { tauri } from '#platform/tauri';

3. The build picks the impl by condition. The web build uses default (browser). The Tauri build activates the tauri condition in vite.config.ts:

const isTauri = process.env.TAURI_ENV_PLATFORM !== undefined;
// ...
resolve: {
	// Custom conditions REPLACE Vite's defaults, so the
	// ...defaultClientConditions spread is LOAD-BEARING (drop it and all
	// dependency resolution breaks).
	...(isTauri && { conditions: ['tauri', ...defaultClientConditions] }),
},

4. tsconfig needs nothing. No moduleSuffixes, no per-target tsconfig. Bundler moduleResolution reads the imports field and lands on default (browser) for the editor and typecheck.

5. Each seam has a shared contract. A types.ts declares the contract; both impls annotate against it with a type annotation, not satisfies:

// platform/types.ts
export type Tauri = { /* ... */ };

// platform/tauri.browser.ts
export const tauri: Tauri | null = null; // no native capability on web

// platform/tauri.tauri.ts
export const tauri: Tauri | null = tauriOnly;

Use export const x: Contract = ..., NOT satisfies. satisfies would leak the concrete type and break the lockstep that keeps both variants conforming to the same shape.

.tauri.ts-only exports bypass the seam. A symbol that only exists on Tauri (e.g. whispering's tauriOnly) is imported DIRECTLY by .tauri.ts files (e.g. import { tauriOnly } from '$lib/tauri.tauri'), not through #platform/* (which resolves to null on web).

The guarantee. Because the wrong-platform file is never resolved, @tauri-apps/* code is PHYSICALLY ABSENT from the web bundle (a build-time guarantee, not Rollup tree-shaking). A Tauri-only file imported by shared code fails the web build instead of shipping a broken runtime.

Why not suffixes

The old mechanism put .browser.ts / .tauri.ts ahead of .ts in Vite resolve.extensions, mirrored by tsconfig moduleSuffixes. That was GLOBAL: every bare import was magic, which is why a bare ./fuji once collided with a fuji.browser.ts. The #platform/* mechanism is scoped to the #platform/* specifiers only, so the rest of the import graph stays ordinary. Do not reintroduce resolve.extensions suffixes or tsconfig moduleSuffixes.

Daemon and Script Placement

Daemon and script bindings are NOT in the app package. They live per-project under workspaces/<app>/ (e.g. playground/opensidian-e2e/workspaces/opensidian/daemon.ts) and are registered through epicenter.config.ts at the Epicenter root:

import { defineConfig } from '@epicenter/workspace';
import opensidian from './workspaces/opensidian/daemon.ts';

export default defineConfig({
	routes: [opensidian],
});

The daemon imports the app's mount factory (the ./mount export) to construct its Mount. epicenter.config.ts marks the Epicenter root and is the route registry; .epicenter/ is machine state under that root, not a discovery marker. The public lifecycle command is epicenter daemon up, not epicenter serve.

Anti-Patterns

• Putting auth, createPersistedState, auth.onStateChange, or HMR disposal in the browser/extension/tauri factory. Those belong in src/lib/session.ts.
• Naming the singleton session.svelte.ts. It is a plain src/lib/session.ts.
• Adding a second singleton home (client.ts) to a Shape A app. The singleton already lives in src/lib/session.ts.
• Putting auth subscriptions or workspace construction in a Svelte component. They belong in the session singleton.
• Branching on platform at a #platform/* call site. Import the bare specifier and let the build select the impl.
• Using satisfies on a #platform/* impl instead of a : Contract annotation.
• Importing a .tauri.ts-only symbol through #platform/* (it is null on web); import it directly from the .tauri module inside another .tauri.ts file.
• Reintroducing resolve.extensions suffixes or tsconfig moduleSuffixes for platform selection.
• Dropping ...defaultClientConditions from the Tauri conditions array.
• Adding a ./browser package export to honeycrisp/vocab/fuji for symmetry with opensidian. Keep the asymmetry; only opensidian has a consumer for it.
• Placing daemon.ts or script.ts inside the app package. They live under a project's workspaces/<app>/ and are registered via epicenter.config.ts.
• Restoring serve as the public lifecycle command (it is epicenter daemon up).