machine_id_stable_source had no Windows arm. It read /etc/machine-id, then
HOSTNAME, then USER -- two UNIX names Windows itself never sets but an
MSYS environment may.
Measured on the box: Git-Bash sets HOSTNAME as a shell variable it does not
export, so a child process reads None, and leaves USER empty. The chain
returned None and the persisted random fallback kept the key stable. Stable by
accident: any environment that exports either name would silently derive a
different key, and a key that moves is a credentials file that no longer
decrypts.
COMPUTERNAME is set by Windows for every process, however the app was
launched, so the value is now stable by construction. Approved with the
one-time re-authentication that moving the key costs; verified by smoke that
no re-authentication was in fact needed, because the master key lives in the
Credential Manager and this derivation is the fallback path.
cc
vicrodh
0c7629b275