fix(filesystem): preserve opaque caller reasons through cleanup

Do not interpret exact caller cancellation reasons as descriptor ownership records. Preserve checkpoint-shaped reasons through successful close retry and supply cancellation context in direct signal-aware cleanup consumers.

Validation: 156 focused tests across 14 files passed; no native provider execution. Refs #4610

src/application/ReferenceSourceImportPolicy.ts

@@ -108,8 +108,9 @@ const buildIgnored = async (
     try {
       text = await readRegularFileText(policyPath, { signal });
     } catch (cause: unknown) {
+      if (signal?.aborted === true && cause === signal.reason) throw cause;
       if (!(cause instanceof RegularFileCleanupFailure)) throw cause;
-      const retry = await retryRegularFileCleanup(cause, resources);
+      const retry = await retryRegularFileCleanup(cause, resources, signal);
       if (retry.cleanup !== undefined) {
         const primary =
           retry.outcome.kind === "failed"