v0.8.5: Extension composability — slots, contributes, lib.require relaxation

Manifest declarations for slots (host surfaces declare injection points)
and contributes (extensions declare UI contributions). lib.require()
relaxed from library-only to any package with exports. Admin slots
aggregation endpoint. SDK renderAll() helper. 7 new tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/sandbox/lib_module.go

@@ -79,19 +79,21 @@ func BuildLibModule(ctx context.Context, r *Runner, consumerPkgID string, rc *Ru
 				return nil, fmt.Errorf("lib.require: package %q does not declare dependency on %q", consumerPkgID, libraryID)
 			}
 
-			// 4. Load library's PackageRegistration
+			// 4. Load target PackageRegistration
 			libPkg, err := r.stores.Packages.Get(ctx, libraryID)
 			if err != nil {
-				return nil, fmt.Errorf("lib.require: library %q not found: %w", libraryID, err)
+				return nil, fmt.Errorf("lib.require: package %q not found: %w", libraryID, err)
 			}
-			if libPkg.Type != "library" {
-				return nil, fmt.Errorf("lib.require: package %q is type %q, not library", libraryID, libPkg.Type)
+			// Any package with exports is callable — not just type "library"
+			exports := extractExports(libPkg.Manifest)
+			if len(exports) == 0 {
+				return nil, fmt.Errorf("lib.require: package %q declares no exports", libraryID)
 			}
 			if libPkg.Status != models.PackageStatusActive {
-				return nil, fmt.Errorf("lib.require: library %q is %s, not active", libraryID, libPkg.Status)
+				return nil, fmt.Errorf("lib.require: package %q is %s, not active", libraryID, libPkg.Status)
 			}
 			if libPkg.Tier != models.ExtTierStarlark {
-				return nil, fmt.Errorf("lib.require: library %q is tier %s, not starlark", libraryID, libPkg.Tier)
+				return nil, fmt.Errorf("lib.require: package %q is tier %s, not starlark", libraryID, libPkg.Tier)
 			}
 
 			// 5. Build library's module set (library's own permissions)
@@ -113,12 +115,7 @@ func BuildLibModule(ctx context.Context, r *Runner, consumerPkgID string, rc *Ru
 				return nil, fmt.Errorf("lib.require: error executing library %q: %w", libraryID, err)
 			}
 
-			// 8. Extract exports from manifest
-			exports := extractExports(libPkg.Manifest)
-			if len(exports) == 0 {
-				return nil, fmt.Errorf("lib.require: library %q declares no exports", libraryID)
-			}
-
+			// 8. Build exported members (exports already extracted above)
 			members := make(starlark.StringDict, len(exports))
 			for _, name := range exports {
 				val, ok := result.Globals[name]