feat: define the module UI authoring model and host contract

ADR 0021 established that a module may own UI and added a statically
validated, never-executed `entrypoints.ui` path, but deliberately left
five questions open: what the artifact exports, what a host provides,
how one artifact runs under both Ekklesia and a standalone host, what
the browser-side trust model is, and how module UI avoids being welded
to a Dashboard that does not exist. This answers them.

React and TypeScript are the supported module UI authoring model. The
repository already leaned this way: `packages/typescript-config` ships a
`browser.json` preset and a `react-native.json` preset with
`"jsx": "react-jsx"`, and ADR 0002 names browser and React Native
configurations. One framework is supported; every other stays rejected.

React is deliberately not part of the contract. A module's compiled
artifact default-exports `defineModuleUi({ id, version, mount })`, and
`mount(container, context)` takes a DOM element and returns an unmount
function. `id` and `version` are build-artifact identity markers a host
verifies against the manifest, mirroring `defineModuleRuntime` exactly.
A host needs an element and a context, never a matching rendering
library, so a module's framework, a host's framework, and the platform
boundary between them stay independent.

The contract lives in a new `@ekklesia/module-ui-sdk` rather than in
`@ekklesia/module-sdk`, for a concrete reason: that package re-exports
all of `@ekklesia/contracts`, so routing module UI through it would drag
Zod, Drizzle, and semver into every browser bundle. The new package has
no runtime dependencies, and its one dependency on contracts is
type-only — the emitted `host-context.js` is `export {};`, and a test
pins that so it cannot regress.

The host context is four members: `moduleId`, `api`, `principal`, and
`permissions`. Navigation, theme, module configuration, organization
context, and diagnostics are deliberately absent; each needs a design
that does not exist. Module UI reaches its backend through
`api.request(path)` with a path relative to its own API root and never
constructs `/api/v1/modules/<id>/...`, which is Ekklesia's private
deployment detail — a module that builds that URL is silently unhostable
anywhere else. One fixture artifact is mounted under two hosts with
different origins and URL shapes to prove it.

Client-side permission hints are presentation only, and both the docs
and a test say so plainly: a denied hint does not stop the module from
calling its API, because server-side `requirePermission` is the only
authority. Module UI is trusted code in the host's own browser realm —
no iframe, no sandbox — which matches the backend model rather than
overstating it, since a module's server half already holds the API's
database authority.

The boundary guard is narrowed precisely, not removed: `.tsx`, `react`,
and `react-dom` are un-denied and modules may depend on the new
`module-ui-sdk` role. `.jsx`, `.css`, every other framework,
`react-router-dom`, `react-native`, and `@vitejs/plugin-react` stay
denied, layer rules are untouched, and an unsupported framework aliased
behind an allowed name (`"react": "npm:vue@3"`) is resolved and rejected
by its real target. Fixtures prove each case, including that module UI
source still cannot import Core.

Core, apps/api, and the manifest contract are untouched. Discovery still
validates the `entrypoints.ui` path and never evaluates it; hosts
perform their own dynamic import and validate the result with
`parseModuleUiExport`. No Dashboard shell, UI runtime, navigation,
grouping, standalone host, build or styling pipeline, installer,
hot-loading, or feature module is added.

Co-Authored-By: Claude Opus 5 <[email protected]>

CONTRIBUTING.md

@@ -33,11 +33,14 @@ pnpm infrastructure:config
 - Expose supported entry points through package `exports`; do not import another package's
   private source paths.
 - Use `workspace:` ranges for internal package dependencies.
-- Module packages cannot contain React, mobile, stylesheet, or other UI source files, and
-  `pnpm boundaries` enforces this. ADR 0021 establishes that a module may own its own UI, but the
-  authoring model — and therefore which parts of that rule change — is a later Phase 6 decision.
-  Until it lands, a module's optional `entrypoints.ui` artifact must be framework-neutral compiled
-  output, and nothing hosts it yet.
+- Modules own their own UI and author it in React and TypeScript (ADR 0022). A module package may
+  contain `.tsx` and depend on `react`, `react-dom`, and `@ekklesia/module-ui-sdk`. Every other UI
+  framework, `.jsx`, stylesheets, and other presentation formats remain rejected by
+  `pnpm boundaries`; module styling and the module UI build pipeline are not designed yet, and no
+  host mounts a UI entrypoint yet.
+- Module UI reaches its host only through `@ekklesia/module-ui-sdk`, and asks the host for its own
+  API by relative path — never by constructing `/api/v1/modules/<id>/...`, which is Ekklesia's
+  private deployment detail and would break standalone hosting.
 - The containing application shell, navigation, global theme, and platform policy belong to Core and
   the host application, never to a module.
 - Add or update tests when changing a contract or architectural rule.