feat: let one module contribute a browser renderer to another's capability

The platform has had a complete story for one module using another's
*backend* since ADR 0006 — capabilities, versioned ranges, provider
registration. It has had none at all for one module using another's *browser*
code, and every workaround is wrong in a way that matters: a consumer cannot
import a peer module, it cannot re-implement a renderer for a domain it does
not own, and a second `entrypoints` role would put the platform in charge of
deciding when a slot inside someone else's screen should be filled.

Add a generic browser contribution. `manifestVersion: 7` declares one:
namespaced id, its own version, a target capability, a compatible range, and
one artifact. That is the complete list, and the omissions are the decision —
no payload schema, slot, ordering, or rendering hint exists anywhere, so Core
cannot learn what a slide is because the declaration cannot express it.

Discovery resolves a contribution artifact through the *identical* loop every
other compiled entrypoint uses, inheriting the path, containment, symlink,
extension, and file-kind checks rather than getting a weaker copy of them. The
registry publishes one only when another eligible module provides the target
capability within the declared range; otherwise it is absent rather than
mounted and broken. `apps/api` serves it as a sibling of the artifact and
display routes, with the same policy: three lookup keys, one exact match, one
already-validated path, and one indistinguishable 404 for unknown, undeclared,
stale, and incompatible alike.

A consumer discovers through the host, never through a URL. Its descriptor
carries identity, version, and capability; the URL stays server-side and is
resolved exactly as `api.request("records")` is. A module can only ever see
contributions aimed at a capability it itself provides, and cannot name its
way to anything else — a mount for a withheld id fails without fetching.

The consumer owns the domain contract entirely. Input is opaque JSON, checked
structurally so a Date, a function, a cycle, or `undefined` fails at the
boundary rather than vanishing somewhere far from the mistake, and checked for
nothing else. A contributed renderer receives its own id and that input: no
API client, realtime, principal, configuration, database, storage, or
credential. Loading one grants its module nothing.

The contribution ABI is versioned separately from the module UI ABI, because
the two have different shapes and lifecycles and coupling them would force
every module to rebuild whenever either moved. It supports asynchronous
readiness, update-without-remount (a screen that remounted per tick would
restart animations and reload media), deterministic cleanup in a `finally`,
and sanitized failure that never carries the consumer's domain data. Each
renderer mounts in its own isolated root with its own stylesheet.

The template now declares a contribution, so `pnpm build` exercises the whole
authoring path, and the shell suite drives the full relationship — one module
discovering, mounting, updating, and unmounting another's React renderer with
neither importing the other.

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

apps/api/src/module-ui-inventory.ts

@@ -1,6 +1,10 @@
 import type { EkklesiaPrincipal, PermissionDeclaration } from "@ekklesia/contracts";
 import { CORE_MODULES_UI_READ } from "@ekklesia/core/authorization";
-import type { ModuleUiPublicationRegistry, PublishableModuleUi } from "@ekklesia/core/modules";
+import type {
+  ModuleUiPublicationRegistry,
+  PublishableModuleContribution,
+  PublishableModuleUi,
+} from "@ekklesia/core/modules";
 import { Hono } from "hono";
 import type { Context } from "hono";
 import {
@@ -10,7 +14,11 @@ import {
 } from "./authorization-middleware.js";
 import { moduleApiBaseUrl } from "./module-http-routes.js";
 import { moduleRealtimeBaseUrl } from "./module-realtime-routes.js";
-import { MODULE_UI_ASSET_PREFIX, moduleUiArtifactUrl } from "./module-ui-routes.js";
+import {
+  MODULE_UI_ASSET_PREFIX,
+  moduleContributionArtifactUrl,
+  moduleUiArtifactUrl,
+} from "./module-ui-routes.js";
 
 /**
  * The collection root of the module UI resource: `/api/v1/module-ui` lists what a browser host may
@@ -64,12 +72,56 @@ export interface HostModuleUiDescriptor {
    * nor trusts anything in this array.
    */
   readonly permissions: readonly string[];
+  /** Renderers other modules contributed to capabilities this module provides (ADR 0041). Empty for
+   * the overwhelming majority of modules, which provide no extension point. */
+  readonly contributions: readonly HostModuleContributionDescriptor[];
+}
+
+/**
+ * One renderer another module contributed to a capability **this** module provides (ADR 0041).
+ *
+ * The URL is server-produced, exactly like `ui.url`, `api.baseUrl`, and `realtime.baseUrl`: a
+ * consuming module names a contribution and the host resolves it, so no module ever builds
+ * Ekklesia's publication URL and every one of them stays hostable elsewhere.
+ *
+ * There is no payload schema, slot, order, or rendering hint here, and there will not be: what a
+ * contributed renderer draws and what shape its input takes are the consuming module's contract,
+ * carried in the browser between two modules without passing through the platform.
+ */
+export interface HostModuleContributionDescriptor {
+  readonly id: string;
+  readonly version: string;
+  /** The capability it was contributed to — one this module declares. */
+  readonly capability: string;
+  readonly url: string;
 }
 
 export interface HostModuleUiInventory {
   readonly modules: readonly HostModuleUiDescriptor[];
 }
 
+/**
+ * The one place a publishable contribution becomes a browser descriptor, shared by the primary-UI
+ * inventory and the display descriptor so the two can never disagree about what a consuming module
+ * may mount.
+ */
+export function describeModuleContributions(
+  registry: ModuleUiPublicationRegistry,
+  moduleId: string,
+): readonly HostModuleContributionDescriptor[] {
+  return registry
+    .contributionsForModule(moduleId)
+    .map((contribution: PublishableModuleContribution) => ({
+      capability: contribution.capability,
+      id: contribution.contributionId,
+      url: moduleContributionArtifactUrl(
+        { moduleId: contribution.moduleId, version: contribution.moduleVersion },
+        contribution.contributionId,
+      ),
+      version: contribution.version,
+    }));
+}
+
 export interface CreateModuleUiInventoryRoutesOptions extends AuthorizationMiddlewareOptions {
   /** The same publication registry the artifact route serves from — the single accepted/publishable
    * module set (`createModuleUiPublicationRegistry`, `@ekklesia/core/modules`). This route performs
@@ -116,9 +168,11 @@ async function describeModule(
   evaluator: AuthorizationMiddlewareOptions["evaluator"],
   principal: EkklesiaPrincipal,
   published: PublishableModuleUi,
+  registry: ModuleUiPublicationRegistry,
 ): Promise<HostModuleUiDescriptor> {
   return {
     api: { baseUrl: moduleApiBaseUrl(published.moduleId) },
+    contributions: describeModuleContributions(registry, published.moduleId),
     id: published.moduleId,
     permissions: await grantedModulePermissionIds(evaluator, principal, published.permissions),
     realtime: { baseUrl: moduleRealtimeBaseUrl(published.moduleId) },
@@ -153,7 +207,7 @@ export async function describeMountableModules(
 ): Promise<readonly MountableModuleDescription[]> {
   return Promise.all(
     registry.list().map(async (published) => ({
-      descriptor: await describeModule(evaluator, principal, published),
+      descriptor: await describeModule(evaluator, principal, published, registry),
       name: published.name,
     })),
   );