fix(director): reject cancellation during the final asset stream read

CHANGELOG.md

@@ -32,6 +32,7 @@
 - Tool string length validation counts Unicode characters correctly, including characters outside the basic multilingual plane.
 
 - Director timeline seeks cross the dateline along the short longitude arc.
+- Director assets cancelled during the final stream read are discarded with reader cleanup.
 
 - Treat explicitly current, complete empty vessel coverage as a successful update,
   clearing obsolete contacts while retaining stale or incomplete snapshots.