Add immutable namespace views

namespaces.go

@@ -0,0 +1,40 @@
+package promptkit
+
+import (
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+// Namespaces selects default resource namespaces for caller-supplied IDs.
+// Empty fields leave that resource type unscoped.
+type Namespaces struct {
+	Prompt  string
+	Profile string
+	Backend string
+}
+
+// WithNamespaces returns an engine view that qualifies slashless prompt and
+// profile selections with the supplied namespaces. Qualified selections pass
+// through unchanged. It replaces all namespace defaults on the new view and
+// leaves the receiver unchanged; resource existence is checked when selected.
+// An empty field clears that resource's scope. Invalid namespace syntax or a
+// nil engine returns an error matching ErrInvalidConfig.
+func (e *Engine) WithNamespaces(namespaces Namespaces) (*Engine, error) {
+	if e == nil || e.internal == nil {
+		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
+	}
+	for _, namespace := range []struct {
+		kind string
+		name string
+	}{
+		{kind: "prompt", name: namespaces.Prompt},
+		{kind: "profile", name: namespaces.Profile},
+		{kind: "backend", name: namespaces.Backend},
+	} {
+		if namespace.name != "" && !domain.IsValidResourceNamespace(namespace.name) {
+			return nil, fmt.Errorf("%w: invalid %s namespace %q", ErrInvalidConfig, namespace.kind, namespace.name)
+		}
+	}
+	return &Engine{internal: e.internal.WithNamespaces(namespaces.Prompt, namespaces.Profile, namespaces.Backend)}, nil
+}