Add snapshotted mapping configuration sources

source.go

@@ -8,7 +8,7 @@ import (
 )
 
 // Source is an opaque configuration input. Construct sources with File,
-// Filesystem.File, Bytes, Reader, or NoSource; the zero value is invalid.
+// Filesystem.File, Bytes, Reader, Mapping, or NoSource; the zero value is invalid.
 type Source struct{ value engine.Source }
 
 // Filesystem is a reusable opaque namespace for a caller-owned fs.FS. Copies
@@ -38,6 +38,15 @@ func Bytes(label string, data []byte) Source { return Source{value: engine.Bytes
 // Copies of the returned Source share the same single-use claim.
 func Reader(label string, input io.Reader) Source { return Source{value: engine.Reader(label, input)} }
 
+// Mapping snapshots supported built-in values immediately. A nil root map is
+// invalid; an empty map is a valid empty document. Values may be nil, built-in
+// scalars, []any, or map[string]any recursively. Unsupported values and cycles
+// are reported when the source is consumed. Label must be nonempty and safe to
+// display. Later caller mutation cannot change the captured document.
+func Mapping(label string, values map[string]any) Source {
+	return Source{value: engine.Mapping(label, values)}
+}
+
 // NoSource explicitly selects a defaults-only input. It creates no source record.
 func NoSource() Source { return Source{value: engine.NoSource()} }