If saving the machine ID to disk fails (e.g., permissions issue), Claude now falls back to an in-memory ID for the current session rather than leaving the field empty. A warning is logged: getOrCreateMachineID: could not persist machineID: <error>.
Evidence
Fallback error log (search for "getOrCreateMachineID: could not persist machineID:")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.