fix(reference): preserve physical failures across late cancellation (#10072)

* fix(reference): preserve physical failures across late cancellation

* fix(reference): retain late cancellation alongside read failures

* fix(reference): preserve metadata errors through cancellation

* fix(reference): retain directory failure identity

* fix(reference): preserve parallel physical and cancellation outcomes

* fix(reference): preserve optional Git metadata absence

src/reference/ReferenceSourceReaderTypes.ts

@@ -88,6 +88,8 @@ export interface ReferenceSourceReaderError {
   readonly message: string;
   readonly remediationAction?: string;
   readonly cleanup?: AnalysisCleanupObservation;
+  /** Exact caller cancellation observed after a distinct failure. */
+  readonly secondaryCancellation?: { readonly cause: unknown };
   /** Captured entries before failure; this does not establish complete tree coverage. */
   readonly partial?: ReferenceSourceRead;
   readonly cause?: unknown;
@@ -117,6 +119,7 @@ export type TraversalState = {
   }>;
   readonly pending: PendingDirectory[];
   rootFailure?: ReferenceSourceRootFailure;
+  rootFailureCause?: { readonly value: unknown };
   bytesRead: number;
 };