Expose native filesystem sources through public loading API

internal/engine/records.go

@@ -11,6 +11,18 @@ const (
 	LayerResolution Layer = "resolution"
 )
 
+// SourceKind identifies source acquisition independently of precedence.
+type SourceKind string
+
+const (
+	SourceKindFile       SourceKind = "file"
+	SourceKindFilesystem SourceKind = "filesystem"
+	SourceKindBytes      SourceKind = "bytes"
+	SourceKindReader     SourceKind = "reader"
+	SourceKindMapping    SourceKind = "mapping"
+	SourceKindCLI        SourceKind = "cli"
+)
+
 // ChangeKind identifies a recorded operation. The zero value is
 // used for input and default origins.
 type ChangeKind string
@@ -156,14 +168,16 @@ type Location struct {
 	Column   int
 }
 
-// SourceInfo describes a source discovered during a load. Path is a canonical
-// local path when one exists. ImportedFrom identifies the declaration that
-// included this source.
+// SourceInfo describes a source discovered during a load. Kind identifies
+// acquisition independently of Layer. Path is a canonical host path or a
+// namespace-relative filesystem path; synthetic sources have no Path.
+// ImportedFrom identifies the declaration that included this source.
 type SourceInfo struct {
 	ID           string
 	Label        string
 	Path         string
 	Layer        Layer
+	Kind         SourceKind
 	ImportedFrom *Location
 }