feat(01-02): dispatch typed events with request context

- App-owned festival bus with Fire, Collect and UntilHandled
- Recover listener panics with owner plugin IDs; isolate buses per app
- towel context accessors and hello command demo of all three modes

towel/context.go

@@ -0,0 +1,63 @@
+package towel
+
+import "context"
+
+type actorKey struct{}
+type organizationKey struct{}
+type collectionKey struct{}
+type localeKey struct{}
+
+func withValue(ctx context.Context, key, value any) context.Context {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	return context.WithValue(ctx, key, value)
+}
+
+func stringValue(ctx context.Context, key any) (string, bool) {
+	if ctx == nil {
+		return "", false
+	}
+	v, ok := ctx.Value(key).(string)
+	return v, ok
+}
+
+// WithActor stores the request actor on ctx.
+func WithActor(ctx context.Context, actor string) context.Context {
+	return withValue(ctx, actorKey{}, actor)
+}
+
+// Actor returns the request actor from ctx.
+func Actor(ctx context.Context) (string, bool) {
+	return stringValue(ctx, actorKey{})
+}
+
+// WithOrganization stores the request organization on ctx.
+func WithOrganization(ctx context.Context, org string) context.Context {
+	return withValue(ctx, organizationKey{}, org)
+}
+
+// Organization returns the request organization from ctx.
+func Organization(ctx context.Context) (string, bool) {
+	return stringValue(ctx, organizationKey{})
+}
+
+// WithCollection stores the request collection on ctx.
+func WithCollection(ctx context.Context, collection string) context.Context {
+	return withValue(ctx, collectionKey{}, collection)
+}
+
+// Collection returns the request collection from ctx.
+func Collection(ctx context.Context) (string, bool) {
+	return stringValue(ctx, collectionKey{})
+}
+
+// WithLocale stores the request locale on ctx.
+func WithLocale(ctx context.Context, locale string) context.Context {
+	return withValue(ctx, localeKey{}, locale)
+}
+
+// Locale returns the request locale from ctx.
+func Locale(ctx context.Context) (string, bool) {
+	return stringValue(ctx, localeKey{})
+}