Add scoped identity listings and backend inventory

internal/engine/engine.go

@@ -94,10 +94,27 @@ type resourceNamespaces struct {
 }
 
 type identityInventory interface {
+	ListBackends(context.Context) ([]string, error)
 	ListProfiles(context.Context) ([]string, error)
 	ListPrompts(context.Context) ([]domain.PromptIdentity, error)
 }
 
+// ListingFilterMode selects namespace membership for one identity listing.
+type ListingFilterMode uint8
+
+const (
+	ListingDefault ListingFilterMode = iota
+	ListingNamed
+	ListingUnqualified
+	ListingAll
+)
+
+// ListingFilter optionally overrides the namespace selected by an engine view.
+type ListingFilter struct {
+	Mode ListingFilterMode
+	Name string
+}
+
 // New assembles an engine from facade-selected configuration and collaborators.
 func New(cfg Config, options Options) (*Engine, error) {
 	defaultRetries, err := domain.ResolveTransientRetries(2, cfg.TransientRetries)
@@ -231,12 +248,99 @@ func (e *Engine) InspectProfile(ctx context.Context, id string) (*domain.Profile
 	return e.runner.InspectProfile(ctx, id)
 }
 
-func (e *Engine) ListProfiles(ctx context.Context) ([]string, error) {
-	return e.listing.ListProfiles(ctx)
+func (e *Engine) ListBackends(ctx context.Context, filters ...ListingFilter) ([]string, error) {
+	return filterIdentityList(ctx, filters, e.namespaces.backend, e.listing.ListBackends)
 }
 
-func (e *Engine) ListPrompts(ctx context.Context) ([]domain.PromptIdentity, error) {
-	return e.listing.ListPrompts(ctx)
+func (e *Engine) ListProfiles(ctx context.Context, filters ...ListingFilter) ([]string, error) {
+	return filterIdentityList(ctx, filters, e.namespaces.profile, e.listing.ListProfiles)
+}
+
+func (e *Engine) ListPrompts(ctx context.Context, filters ...ListingFilter) ([]domain.PromptIdentity, error) {
+	mode, namespace, err := resolveListingFilter(filters, e.namespaces.prompt)
+	if err != nil {
+		return nil, err
+	}
+	prompts, err := e.listing.ListPrompts(ctx)
+	if err != nil {
+		return nil, err
+	}
+	var filtered []domain.PromptIdentity
+	for _, prompt := range prompts {
+		if matchesListingNamespace(prompt.ID, mode, namespace) {
+			filtered = append(filtered, prompt)
+		}
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	return filtered, nil
+}
+
+func filterIdentityList(
+	ctx context.Context,
+	filters []ListingFilter,
+	scope string,
+	list func(context.Context) ([]string, error),
+) ([]string, error) {
+	mode, namespace, err := resolveListingFilter(filters, scope)
+	if err != nil {
+		return nil, err
+	}
+	ids, err := list(ctx)
+	if err != nil {
+		return nil, err
+	}
+	var filtered []string
+	for _, id := range ids {
+		if matchesListingNamespace(id, mode, namespace) {
+			filtered = append(filtered, id)
+		}
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	return filtered, nil
+}
+
+func resolveListingFilter(filters []ListingFilter, scope string) (ListingFilterMode, string, error) {
+	if len(filters) > 1 {
+		return 0, "", fmt.Errorf("%w: at most one listing filter is allowed", usecase.ErrInvalidRequest)
+	}
+	filter := ListingFilter{}
+	if len(filters) == 1 {
+		filter = filters[0]
+	}
+	switch filter.Mode {
+	case ListingDefault:
+		if scope == "" {
+			return ListingAll, "", nil
+		}
+		return ListingNamed, scope, nil
+	case ListingNamed:
+		if !domain.IsValidResourceNamespace(filter.Name) {
+			return 0, "", fmt.Errorf("%w: invalid listing namespace", usecase.ErrInvalidRequest)
+		}
+		return ListingNamed, filter.Name, nil
+	case ListingUnqualified, ListingAll:
+		return filter.Mode, "", nil
+	default:
+		return 0, "", fmt.Errorf("%w: unknown listing filter mode", usecase.ErrInvalidRequest)
+	}
+}
+
+func matchesListingNamespace(id string, mode ListingFilterMode, namespace string) bool {
+	switch mode {
+	case ListingNamed:
+		idNamespace, _, qualified := strings.Cut(id, "/")
+		return qualified && idNamespace == namespace
+	case ListingUnqualified:
+		return !strings.Contains(id, "/")
+	case ListingAll:
+		return true
+	default:
+		return false
+	}
 }
 func (e *Engine) Prepare(ctx context.Context, request domain.RunRequest) (*domain.PreparedRun, error) {
 	request, err := e.qualifyRunRequest(request)