Policy-limits cache no longer overwrites its stamp when the existing one can't be read
When Claude Code saves updated policy-limits data to its local cache, it now first checks whether it could actually read the existing on-disk "stamp" (a marker used to track the cache state). If that read failed, the save is aborted entirely for that cycle and nothing is written, with a log noting the cache stamp could not be read. Previously it would proceed to overwrite regardless.
A companion testing-only method, _settleCyclesForTesting, was also added to let tests wait for all in-progress fetch cycles to finish.
This avoids silently clobbering the policy-limits cache when its current state can't be verified, reducing the chance of corrupting or losing track of cached policy data.