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]>

surfaces/shell/tests/modularity.test.ts

@@ -135,14 +135,15 @@ describe("the shell builds no module knowledge into its bundle", () => {
     bundle = result.outputFiles.map((file) => file.text).join("\n");
   }, 60_000);
 
-  it("leaves exactly one dynamic import — the loader's — unresolved for run time", () => {
+  it("leaves exactly the generic loaders' dynamic imports unresolved for run time", () => {
     const dynamicImports = [...bundle.matchAll(/\bimport\s*\(/gu)];
 
-    // Exactly one: `@ekklesia/module-ui-host`'s `(url) => import(url)`. More would mean the shell
-    // acquired its own loader; fewer would mean the bundler resolved it away and installed modules
-    // could never be fetched at run time.
-    expect(dynamicImports).toHaveLength(1);
-    expect(bundle).toContain("(url) => import(url)");
+    // Exactly two, both `@ekklesia/module-ui-host`'s `(url) => import(url)`: one for a module UI
+    // artifact and one for a contributed renderer (ADR 0041). More would mean the shell acquired a
+    // loader of its own; fewer would mean the bundler resolved one away and installed code could
+    // never be fetched at run time.
+    expect(dynamicImports).toHaveLength(2);
+    expect(bundle.split("(url) => import(url)")).toHaveLength(3);
   });
 
   it("contains no module identity and no module API prefix", () => {
@@ -214,9 +215,10 @@ describe("the display host is a separate generic browser bundle", () => {
     bundle = result.outputFiles.map((file) => file.text).join("\n");
   }, 60_000);
 
-  it("contains the generic loader's one dynamic import and no statically known module", () => {
-    expect([...bundle.matchAll(/\bimport\s*\(/gu)]).toHaveLength(1);
-    expect(bundle).toContain("(url) => import(url)");
+  it("contains the generic loaders' dynamic imports and no statically known module", () => {
+    // Two, both the generic loader's: a display artifact and a contributed renderer (ADR 0041).
+    expect([...bundle.matchAll(/\bimport\s*\(/gu)]).toHaveLength(2);
+    expect(bundle.split("(url) => import(url)")).toHaveLength(3);
     expect(bundle).not.toContain("ekklesia.module.json");
     expect(bundle).not.toContain("/api/v1/modules");
     for (const moduleId of ["announcements", "calendar", "livestream", "signage"]) {