Platform seams

Replaces workspace-app-composition, whose subject (defineWorkspace, the workspace singleton, environment factories, the daemon) was deleted with the workspace plane. The seam below is the part that survived.

Storage is not a seam

Every build opens its own store. A host serves bundles and brokers credentials and owns no application data (ADR-0226), so there is no build where data lives somewhere else, and a #platform/* seam for storage is the thing to delete rather than to route. Honeycrisp calls openBrowserStore in every build including the Tauri one, and apps/honeycrisp/src/lib/application-platform.ts states that as a refusal with its reasons.

What is left behind a seam is how a build gets a bearer and which deployment it talks to, plus native capability. Honeycrisp declares exactly two: #platform/auth and #platform/instance.

Declaring one

1. Map the specifier in package.json "imports". One entry per condition, plus a default:

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

Condition order in the map is match order.

2. Import the bare specifier, with no branch at the call site:

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

3. Activate the condition in vite.config.ts:

resolve: {
	// Custom conditions REPLACE Vite's defaults, so the
	// ...defaultClientConditions spread is LOAD-BEARING: drop it and all
	// dependency resolution breaks.
	...(isEpicenterSurface && {
		conditions: ['tauri', ...defaultClientConditions],
	}),
},

4. Typecheck every leaf. Bundler moduleResolution reads the imports field and lands on default for the editor, so the browser leaf is free. Every other condition needs its own tsconfig.<condition>.json setting compilerOptions.customConditions, run from typecheck. Without one, those leaves are never checked at all.

5. Give the seam a contract. types.ts declares it; each leaf annotates against it:

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

// platform/auth.browser.ts
export const auth: PlatformAuth | undefined = browserAuth;

Use export const x: Contract = ..., not satisfies. satisfies leaks the concrete type and breaks the lockstep that keeps every leaf the same shape.

The two conditions answer different questions (ADR-0190)

tauri means this build runs in a Tauri WebView, so a leaf may call a native command. epicenter-host means the desktop Epicenter host serves this build, so a leaf may reach the host for a credential, a deployment choice, or an asset base.

They used to be conflated because epicenter-host also meant the host owned the build's replica. ADR-0226 removed that, so the condition is now about brokered credentials and nothing about data.

A build that owns its own storage uses neither host condition, whether a browser or a bundle serves it: a WebView is a storage partition and origin pair like any other (ADR-0177). Every build owns its own storage, so this is now always true.

A dropped leaf fails nothing

This is the one hazard worth remembering. Removing an epicenter-host key from a seam breaks no build: resolution falls back silently to default, and the hosted build quietly runs the browser leaf. apps/honeycrisp/src/lib/platform-selection.test.ts reads the declarations and names the broken seam, and apps/epicenter/scripts/build-applications.test.ts runs the real build and reads the emitted bytes.

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 how a bare ./fuji once collided with a fuji.browser.ts. #platform/* is scoped to those specifiers only, so the rest of the import graph stays ordinary.

Anti-patterns

• Adding a #platform/* seam for storage, a replica, or a database. Every build opens its own store; that seam is what ADR-0226 refused.
• Branching on the platform at a #platform/* call site. Import the bare specifier and let the build select the leaf.
• Detecting the host at runtime. The build already answered.
• Using satisfies on a leaf instead of a : Contract annotation.
• Importing a .tauri.ts-only symbol through #platform/*. It resolves to the browser leaf off Tauri; import it directly from the .tauri module inside another .tauri.ts file.
• Reintroducing resolve.extensions suffixes or tsconfig moduleSuffixes.
• Dropping ...defaultClientConditions from the Tauri conditions array.
• Adding a condition leaf with no tsconfig.<condition>.json, which means it is never typechecked.
• Gating a route or the app shell on identity: no (signed-in) route groups, no signed-out screen, no redirect-to-sign-in. Sign-in is an enhancement (ADR-0088), and signed-in-only features get small inline affordances.