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/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)
+	}
+}