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>

CHANGELOG.md

@@ -2,6 +2,68 @@
 
 All notable changes to Armature are documented here.
 
+## v0.8.5 — Extension Composability
+
+Extensions can now compose with each other through declared slots, UI
+contributions, and cross-package function calls. This is the last kernel
+feature before 1.0 — the platform now supports the "extensions extending
+extensions" pattern.
+
+**Manifest declarations**
+
+- Surfaces declare named `slots` in their manifest (e.g., `toolbar-actions`,
+  `note-footer`) with context documentation for extension authors.
+- Extensions declare `contributes` entries targeting `{host}:{slot}` names
+  (e.g., `notes:toolbar-actions`). Coupling is soft — install order doesn't
+  matter.
+- The kernel validates slot/contribution conventions at install time.
+
+**Backend: `lib.require()` relaxation**
+
+- `lib.require()` now works with any package that declares `exports`, not
+  just `type: "library"` packages. A full package (with surfaces, settings,
+  UI) can export callable functions for cross-package use.
+- The existing `depends` and permission model is unchanged — the called
+  function runs with the target package's permissions.
+
+**Admin slots endpoint**
+
+- `GET /api/v1/admin/slots` returns an aggregated map of all declared slots
+  across installed packages with their contributors.
+- Uninstalling a package that declares slots warns about orphaned
+  contributions in other packages.
+
+**SDK additions**
+
+- `sw.slots.renderAll(name, context)` — convenience helper for host surfaces
+  to render all components in a slot with error isolation.
+- `sw.slots.declare(name, description)` — runtime slot declaration for
+  discoverability and debugging.
+
+**Documentation**
+
+- `PACKAGE-FORMAT.md` — added `slots`, `contributes`, `depends` field docs.
+- `EXTENSION-GUIDE.md` — new "Extension Composability" section with slot
+  naming conventions, contribution patterns, and cross-package call examples.
+- `STARLARK-REFERENCE.md` — updated `lib` module to reflect exports-based
+  calling (not library-type-only).
+
+**Modified files:**
+
+- `server/sandbox/lib_module.go` — type check → exports check
+- `server/handlers/extensions.go` — composability field validation
+- `server/handlers/packages.go` — orphaned contribution warning
+- `server/main.go` — admin slots route registration
+- `src/js/sw/sdk/slots.js` — `renderAll()`, `declare()`, `declarations()`
+- `docs/PACKAGE-FORMAT.md` — slots, contributes, depends
+- `docs/EXTENSION-GUIDE.md` — composability section
+- `docs/STARLARK-REFERENCE.md` — lib module update
+- `docs/DESIGN-extension-composability.md` — status Draft → Implemented
+
+**New files:**
+
+- `server/handlers/admin_slots.go` — admin slot aggregation endpoint
+
 ## v0.8.4 — Documentation Refresh + Surface Sizing Fix
 
 Eight versions of module additions (v0.7.5–v0.8.3) shipped without a

ROADMAP.md

@@ -1,6 +1,6 @@
 # Armature — Roadmap
 
-## Current: v0.8.5 — Extension Composability
+## Current: v0.8.5 — Extension Composability (Kernel Complete)
 
 Self-hosted extensible platform kernel. Auth, identity, packages, Starlark
 sandbox, storage, realtime, and ops are kernel primitives. Everything else
@@ -444,7 +444,7 @@ sizing fix: `.surface-inner` converted to flex column layout so the shell
 topbar and surface container share vertical space correctly — eliminates
 44px scroll cutoff on all surfaces.
 
-**v0.8.5 — Extension Composability**
+**v0.8.5 — Extension Composability** ✅
 
 Design doc: `docs/DESIGN-extension-composability.md`
 
@@ -453,14 +453,16 @@ and `contributes` (extensions declare UI contributions to other packages'
 slots). `lib.require()` relaxed from library-only to any package with
 `exports` — enables full packages (with surfaces, settings, UI) to also
 expose callable backend functions. `sw.slots.renderAll()` SDK helper.
-Admin slot aggregation endpoint.
+Admin slot aggregation endpoint. Uninstall orphan warnings.
 
 The composability primitive that enables: LLM tool registration, UI
 contribution (toolbar buttons, image actions), and cross-extension
 function calls. No new tables, migrations, or permissions.
 
-Modified: `sandbox/lib_module.go` (~1 line), `handlers/extensions.go`,
-`src/js/sw/sdk/slots.js`. New: `handlers/admin_slots.go`.
+Modified: `sandbox/lib_module.go`, `handlers/extensions.go`,
+`handlers/packages.go`, `src/js/sw/sdk/slots.js`, `server/main.go`.
+New: `handlers/admin_slots.go`. Docs: PACKAGE-FORMAT, EXTENSION-GUIDE,
+STARLARK-REFERENCE updated.
 
 ---
 

VERSION

@@ -1 +1 @@
-0.8.4
+0.8.5

docs/DESIGN-extension-composability.md

@@ -1,7 +1,7 @@
 # DESIGN — Extension Composability
 
-**Version:** v0.8.4
-**Status:** Draft
+**Version:** v0.8.5
+**Status:** Implemented
 **Author:** Jeff / Claude session 2026-04-02
 
 ---

docs/EXTENSION-GUIDE.md

@@ -77,7 +77,10 @@ Every package has a `manifest.json` at its root. Example for a surface:
 | `api_schema` | no | OpenAPI documentation for extension API routes (see below) |
 | `db_tables` | no | Table definitions (see below) |
 | `settings` | no | User-configurable settings schema |
-| `exports` | libraries | Functions exported for other packages |
+| `exports` | no | Functions exported for cross-package calls via `lib.require()` |
+| `depends` | no | Array of package IDs this package depends on |
+| `slots` | no | Named UI injection points for host surfaces |
+| `contributes` | no | Slot contributions into other surfaces |
 | `hooks` | no | Event bus subscriptions |
 | `config_section` | no | Settings/Admin panel injection (see below) |
 | `capabilities` | no | Environment requirements (see below) |
@@ -194,6 +197,117 @@ sandbox permission model.
 In Starlark, check permissions inline via `req["permissions"]` or call
 `permissions.check(user_id, "image-gen.use")`.
 
+## Extension Composability
+
+Extensions compose with each other through three mechanisms: manifest-declared
+**slots** (UI injection points), **contributions** (UI components injected into
+those slots), and cross-package **function calls** via `lib.require()`.
+
+### Slots — Host Surfaces Declare Injection Points
+
+A surface declares named slots in its manifest where other extensions can
+inject UI components:
+
+```json
+{
+  "id": "notes",
+  "type": "surface",
+  "slots": {
+    "toolbar-actions": {
+      "description": "Toolbar action buttons",
+      "context": {
+        "noteId": "string",
+        "getContent": "function — returns note body",
+        "setContent": "function — replaces note body"
+      }
+    }
+  }
+}
+```
+
+The surface renders slot contents using the SDK helper:
+
+```javascript
+html`<div class="toolbar">
+    ${sw.slots.renderAll('notes:toolbar-actions', {
+        noteId: note.id,
+        getContent: () => editor.getValue(),
+        setContent: (text) => editor.setValue(text),
+    })}
+</div>`
+```
+
+### Contributions — Extensions Inject UI
+
+An extension declares which slots it contributes to:
+
+```json
+{
+  "id": "note-dictate",
+  "type": "extension",
+  "contributes": {
+    "notes:toolbar-actions": {
+      "label": "Dictate",
+      "icon": "🎤",
+      "description": "Voice-to-text dictation"
+    }
+  }
+}
+```
+
+In its JavaScript, it registers the component:
+
+```javascript
+sw.slots.register('notes:toolbar-actions', {
+    id: 'note-dictate',
+    priority: 200,
+    component: ({ noteId, setContent, getContent }) => {
+        // ... component implementation
+        return html`<button class="sw-btn sw-btn--ghost">🎤</button>`;
+    }
+});
+```
+
+Contributions are soft-coupled — install order doesn't matter. The admin
+can view all slots and contributors at **Admin > Packages** or via
+`GET /api/v1/admin/slots`.
+
+### Cross-Package Function Calls
+
+Any package that declares `exports` in its manifest can be called by other
+packages via `lib.require()`. The caller declares the dependency:
+
+```json
+{
+  "id": "note-ai",
+  "depends": ["llm-bridge"],
+  "permissions": ["api.http"]
+}
+```
+
+In Starlark:
+
+```python
+llm = lib.require("llm-bridge")
+result = llm.complete([{"role": "user", "content": prompt}])
+```
+
+The called function runs with the *target* package's permissions, not the
+caller's. This is the same security model as library packages.
+
+### Slot Naming Convention
+
+Slot names follow `{host-package-id}:{slot-name}`. The colon separates the
+namespace from the slot. Standard slots for first-party packages:
+
+| Slot | Host | Use Case |
+|------|------|----------|
+| `notes:toolbar-actions` | notes | Dictation, AI tools, formatting |
+| `notes:note-footer` | notes | Related items, AI summary |
+| `chat:composer-tools` | chat | Image gen, file attach |
+| `chat:message-actions` | chat | Reactions, translate, bookmark |
+| `chat:image-actions` | chat | Regen, edit, upscale |
+
 ## Starlark Sandbox API
 
 Starlark scripts run server-side with a 1M operation budget and no

docs/PACKAGE-FORMAT.md

@@ -68,10 +68,66 @@ Only `manifest.json` is required. All other directories are optional and include
 | `db_tables` | Table definitions with columns and indexes |
 | `settings` | User-configurable settings with type, label, description, default |
 | `hooks` | Event bus subscription patterns |
-| `exports` | Functions exported by library packages |
+| `exports` | Functions exported for cross-package calls via `lib.require()` |
+| `depends` | Array of package IDs this package depends on |
+| `slots` | Named UI injection points (host surfaces declare these) |
+| `contributes` | Slot contributions this package injects into other surfaces |
 | `capabilities` | Environment requirements: `{"required": [...], "optional": [...]}` |
 | `schema_version` | Integer for additive schema migrations |
 
+## Composability: Slots and Contributions
+
+Packages compose with each other through named UI injection points (**slots**) and **contributions**.
+
+### Declaring Slots (Host Surfaces)
+
+Surfaces declare slots where other extensions can inject UI:
+
+```json
+{
+  "slots": {
+    "toolbar-actions": {
+      "description": "Toolbar action buttons",
+      "context": {
+        "noteId": "string — current note ID",
+        "getContent": "function — returns note body text"
+      }
+    }
+  }
+}
+```
+
+Slot names are namespaced at runtime as `{package-id}:{slot-name}` (e.g., `notes:toolbar-actions`). The `context` field documents what data the slot provides — it is not enforced at runtime.
+
+### Contributing to Slots
+
+Extensions declare which slots they inject into:
+
+```json
+{
+  "contributes": {
+    "notes:toolbar-actions": {
+      "label": "Dictate",
+      "icon": "🎤",
+      "description": "Voice-to-text dictation"
+    }
+  }
+}
+```
+
+Contributing extensions can be installed before or after their host surface — the coupling is soft. The admin can view all slots and their contributors at `GET /api/v1/admin/slots`.
+
+### Cross-Package Function Calls
+
+Any package that declares `exports` can be called via `lib.require()`, not just library-type packages. The caller must declare the target in its `depends` array:
+
+```json
+{
+  "depends": ["image-gen"],
+  "permissions": ["api.http"]
+}
+```
+
 ## Package Lifecycle
 
 1. **Install**: Upload a `.pkg` file via Admin > Packages or `POST /api/v1/admin/packages/install`. The kernel extracts the archive, creates database tables, and registers routes.

docs/STARLARK-REFERENCE.md

@@ -50,7 +50,7 @@ is detected by the kernel. Detected capabilities: `pgvector`, `workspace`,
 
 ### lib
 
-Load exported functions from library packages.
+Load exported functions from other packages.
 
 ```python
 helpers = lib.require("my-utils")
@@ -58,11 +58,17 @@ result = helpers.format_date("2026-01-15")
 ```
 
 Requirements:
-- The library must be declared in your package manifest's `dependencies`.
-- The library must be type `library`, status `active`, tier `starlark`.
+- The target package must be declared in your manifest's `depends` array.
+- The target package must declare `exports` in its manifest.
+- The target package must be status `active`, tier `starlark`.
+- Any package type (`library`, `extension`, `full`) can be called as long
+  as it declares exports. This enables full packages to expose callable
+  functions alongside their UI and API routes.
 - Circular dependencies are detected and rejected.
 - Results are cached per execution (calling `require` twice returns the
   same object).
+- The called function runs with the *target* package's permissions, not
+  the caller's.
 
 ### permissions
 

server/handlers/admin_slots.go

@@ -0,0 +1,96 @@
+package handlers
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+// slotInfo describes a declared slot and its contributors.
+type slotInfo struct {
+	Host         string           `json:"host"`
+	Description  string           `json:"description"`
+	Context      map[string]any   `json:"context,omitempty"`
+	Contributors []slotContributor `json:"contributors"`
+}
+
+// slotContributor describes one package's contribution to a slot.
+type slotContributor struct {
+	Package     string `json:"package"`
+	Label       string `json:"label,omitempty"`
+	Icon        string `json:"icon,omitempty"`
+	Description string `json:"description,omitempty"`
+}
+
+// ListSlots returns an aggregated map of all declared slots across installed
+// packages together with their contributors. Built on-the-fly from manifests.
+// GET /api/v1/admin/slots
+func (h *PackageHandler) ListSlots(c *gin.Context) {
+	pkgs, err := h.stores.Packages.List(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list packages"})
+		return
+	}
+
+	slots := map[string]*slotInfo{}
+
+	// Pass 1: collect declared slots from host surfaces
+	for _, pkg := range pkgs {
+		slotsRaw, ok := pkg.Manifest["slots"].(map[string]any)
+		if !ok {
+			continue
+		}
+		for name, v := range slotsRaw {
+			fullName := pkg.ID + ":" + name
+			entry, ok := v.(map[string]any)
+			if !ok {
+				continue
+			}
+			desc, _ := entry["description"].(string)
+			var ctx map[string]any
+			if c, ok := entry["context"].(map[string]any); ok {
+				ctx = c
+			}
+			slots[fullName] = &slotInfo{
+				Host:         pkg.ID,
+				Description:  desc,
+				Context:      ctx,
+				Contributors: []slotContributor{},
+			}
+		}
+	}
+
+	// Pass 2: collect contributions
+	for _, pkg := range pkgs {
+		if !pkg.Enabled {
+			continue
+		}
+		contribs, ok := pkg.Manifest["contributes"].(map[string]any)
+		if !ok {
+			continue
+		}
+		for slotKey, v := range contribs {
+			// Ensure the slot entry exists (contributor can arrive before host)
+			if _, exists := slots[slotKey]; !exists {
+				host := slotKey
+				if idx := strings.Index(slotKey, ":"); idx >= 0 {
+					host = slotKey[:idx]
+				}
+				slots[slotKey] = &slotInfo{
+					Host:         host,
+					Contributors: []slotContributor{},
+				}
+			}
+			contrib := slotContributor{Package: pkg.ID}
+			if m, ok := v.(map[string]any); ok {
+				contrib.Label, _ = m["label"].(string)
+				contrib.Icon, _ = m["icon"].(string)
+				contrib.Description, _ = m["description"].(string)
+			}
+			slots[slotKey].Contributors = append(slots[slotKey].Contributors, contrib)
+		}
+	}
+
+	c.JSON(http.StatusOK, gin.H{"data": slots})
+}

server/handlers/composability_test.go

@@ -0,0 +1,97 @@
+package handlers
+
+import (
+	"testing"
+)
+
+func TestValidateComposabilityFields_ValidSlots(t *testing.T) {
+	m := map[string]any{
+		"slots": map[string]any{
+			"toolbar-actions": map[string]any{
+				"description": "Toolbar action buttons",
+				"context": map[string]any{
+					"noteId": "string",
+				},
+			},
+		},
+	}
+	if err := ValidateComposabilityFields(m); err != "" {
+		t.Errorf("expected valid, got: %s", err)
+	}
+}
+
+func TestValidateComposabilityFields_SlotMissingDescription(t *testing.T) {
+	m := map[string]any{
+		"slots": map[string]any{
+			"toolbar": map[string]any{
+				"context": map[string]any{},
+			},
+		},
+	}
+	if err := ValidateComposabilityFields(m); err == "" {
+		t.Error("expected error for slot missing description")
+	}
+}
+
+func TestValidateComposabilityFields_SlotsNotObject(t *testing.T) {
+	m := map[string]any{
+		"slots": "bad",
+	}
+	if err := ValidateComposabilityFields(m); err == "" {
+		t.Error("expected error for non-object slots")
+	}
+}
+
+func TestValidateComposabilityFields_ValidContributes(t *testing.T) {
+	m := map[string]any{
+		"contributes": map[string]any{
+			"notes:toolbar-actions": map[string]any{
+				"label": "Dictate",
+				"icon":  "🎤",
+			},
+		},
+	}
+	if err := ValidateComposabilityFields(m); err != "" {
+		t.Errorf("expected valid, got: %s", err)
+	}
+}
+
+func TestValidateComposabilityFields_ContributesMissingColon(t *testing.T) {
+	m := map[string]any{
+		"contributes": map[string]any{
+			"toolbar-actions": map[string]any{
+				"label": "Bad",
+			},
+		},
+	}
+	if err := ValidateComposabilityFields(m); err == "" {
+		t.Error("expected error for contributes key without colon")
+	}
+}
+
+func TestValidateComposabilityFields_Empty(t *testing.T) {
+	m := map[string]any{
+		"id": "test",
+	}
+	if err := ValidateComposabilityFields(m); err != "" {
+		t.Errorf("expected valid for manifest without slots/contributes, got: %s", err)
+	}
+}
+
+func TestValidateComposabilityFields_BothValid(t *testing.T) {
+	m := map[string]any{
+		"slots": map[string]any{
+			"my-slot": map[string]any{
+				"description": "A slot",
+			},
+		},
+		"contributes": map[string]any{
+			"other:their-slot": map[string]any{
+				"label": "Hello",
+			},
+		},
+	}
+	if err := ValidateComposabilityFields(m); err != "" {
+		t.Errorf("expected valid, got: %s", err)
+	}
+}

server/handlers/extensions.go

@@ -37,6 +37,44 @@ var validTiers = map[string]bool{
 	models.ExtTierSidecar:  true,
 }
 
+// ValidateComposabilityFields checks that manifest slots and contributes
+// fields follow the expected conventions. Slots values must have a
+// "description" string. Contributes keys must follow "pkg:slot" naming.
+// Returns nil if valid or missing; returns an error string otherwise.
+func ValidateComposabilityFields(manifest map[string]any) string {
+	// Validate slots: map of name → {description, ...}
+	if slotsRaw, ok := manifest["slots"]; ok {
+		slots, ok := slotsRaw.(map[string]any)
+		if !ok {
+			return "slots must be an object"
+		}
+		for name, v := range slots {
+			entry, ok := v.(map[string]any)
+			if !ok {
+				return "slots." + name + " must be an object"
+			}
+			if _, ok := entry["description"]; !ok {
+				return "slots." + name + " must have a description"
+			}
+		}
+	}
+
+	// Validate contributes: map of "pkg:slot" → {label, ...}
+	if contribRaw, ok := manifest["contributes"]; ok {
+		contribs, ok := contribRaw.(map[string]any)
+		if !ok {
+			return "contributes must be an object"
+		}
+		for key := range contribs {
+			if !strings.Contains(key, ":") {
+				return "contributes key " + key + " must follow pkg:slot convention"
+			}
+		}
+	}
+
+	return ""
+}
+
 // ── User endpoints ──────────────────────────────
 
 // ListUserExtensions returns all enabled extensions for the current user,
@@ -208,6 +246,12 @@ func (h *ExtensionHandler) AdminInstallExtension(c *gin.Context) {
 		manifestMap = map[string]any{}
 	}
 
+	// Validate composability fields (slots / contributes)
+	if errMsg := ValidateComposabilityFields(manifestMap); errMsg != "" {
+		c.JSON(400, gin.H{"error": "manifest: " + errMsg})
+		return
+	}
+
 	pkg := &store.PackageRegistration{
 		ID:          body.ExtID,
 		Title:       body.Name,

server/handlers/packages.go

@@ -212,10 +212,48 @@ func (h *PackageHandler) DeletePackage(c *gin.Context) {
 		}
 	}
 
-	c.JSON(http.StatusOK, gin.H{"id": id, "deleted": true})
+	resp := gin.H{"id": id, "deleted": true}
+
+	// Warn about orphaned slot contributions
+	if orphaned := findOrphanedContributors(c, h.stores, id); len(orphaned) > 0 {
+		resp["warning"] = "slot contributions orphaned in: " + strings.Join(orphaned, ", ")
+	}
+
+	c.JSON(http.StatusOK, resp)
 	h.broadcastPackageChanged("deleted", id)
 }
 
+// findOrphanedContributors returns package IDs that declare contributes
+// targeting slots owned by the given package (e.g. "notes:toolbar-actions"
+// targets the "notes" package). This is a warning, not a blocker.
+func findOrphanedContributors(c *gin.Context, stores store.Stores, deletedPkgID string) []string {
+	allPkgs, err := stores.Packages.List(c.Request.Context())
+	if err != nil {
+		return nil
+	}
+	prefix := deletedPkgID + ":"
+	seen := map[string]bool{}
+	for _, p := range allPkgs {
+		if p.ID == deletedPkgID || !p.Enabled {
+			continue
+		}
+		contribs, ok := p.Manifest["contributes"].(map[string]any)
+		if !ok {
+			continue
+		}
+		for key := range contribs {
+			if strings.HasPrefix(key, prefix) {
+				seen[p.ID] = true
+			}
+		}
+	}
+	result := make([]string, 0, len(seen))
+	for id := range seen {
+		result = append(result, id)
+	}
+	return result
+}
+
 // InstallPackage uploads and installs a .pkg/.surface archive.
 // POST /api/v1/admin/packages/install
 //
@@ -466,6 +504,13 @@ func (h *PackageHandler) parseAndValidateArchive(c *gin.Context, tmpPath string)
 		return nil, nil, nil, err
 	}
 
+	// Validate composability fields (slots / contributes)
+	if errMsg := ValidateComposabilityFields(manifest); errMsg != "" {
+		zr.Close()
+		c.JSON(http.StatusBadRequest, gin.H{"error": "manifest: " + errMsg})
+		return nil, nil, nil, fmt.Errorf("invalid composability fields")
+	}
+
 	// Signing hook (reserved)
 	if os.Getenv("PACKAGE_VERIFY_SIGNATURES") == "true" {
 		if mInfo.Signature != "" {

server/main.go

@@ -859,6 +859,7 @@ func main() {
 			admin.POST("/packages/:id/update", pkgAdm.UpdatePackage)
 			admin.GET("/packages/:id/export", pkgAdm.ExportPackage)
 			admin.GET("/dependencies", pkgAdm.ListAllDependencies)
+			admin.GET("/slots", pkgAdm.ListSlots)
 
 			// Workflow package export
 			wfPkgH := handlers.NewWorkflowPackageHandler(stores)

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]

src/js/sw/sdk/slots.js

@@ -15,6 +15,8 @@
 export function createSlots(emitFn) {
     /** @type {Map<string, Array<{id:string, component:Function, priority:number}>>} */
     const _registry = new Map();
+    /** @type {Map<string, string>|undefined} */
+    let _declarations;
 
     function _sort(arr) {
         arr.sort((a, b) => a.priority - b.priority);
@@ -73,5 +75,43 @@ export function createSlots(emitFn) {
         names() {
             return [..._registry.keys()];
         },
+
+        /**
+         * Render all components registered in a slot.
+         * Each component is called with the context object. Errors are
+         * caught so one broken contributor doesn't break the host surface.
+         * @param {string} name — slot name
+         * @param {object} context — props passed to each component
+         * @returns {Array} — array of rendered vnodes (nulls filtered)
+         */
+        renderAll(name, context = {}) {
+            return this.get(name).map(e => {
+                try {
+                    return e.component(context);
+                } catch (err) {
+                    console.error(`[sw.slots] Error rendering "${e.id}" in slot "${name}":`, err);
+                    return null;
+                }
+            }).filter(Boolean);
+        },
+
+        /**
+         * Declare a slot for discoverability. Runtime-only metadata —
+         * does not affect registration or rendering.
+         * @param {string} name — slot name
+         * @param {string} description — human-readable purpose
+         */
+        declare(name, description) {
+            if (!_declarations) _declarations = new Map();
+            _declarations.set(name, description);
+        },
+
+        /**
+         * List declared slot metadata (from declare()).
+         * @returns {Map<string, string>}
+         */
+        declarations() {
+            return _declarations ? new Map(_declarations) : new Map();
+        },
     };
 }