Two defects in the stage 0 bootstrap, both surfacing as "Access denied" on a
server where the operator was holding the correct password.
CREATE USER IF NOT EXISTS is a no-op on an existing user - it does NOT change
the password. Stage 0 generates a fresh password every run and overwrites
.dbpass with it unconditionally, so any path that re-runs the bootstrap over an
existing account left the handoff holding a password the server had never been
told. ALTER USER now follows each CREATE, so the stored password and the handoff
always agree.
The user was also only created for 'localhost' and '127.0.0.1'. On current
Windows, 'localhost' resolves to the IPv6 loopback FIRST, so an operator who
types localhost rather than 127.0.0.1 arrives as '<user>'@'::1' - an account
that did not exist - and MySQL answers "Access denied" naming a host they never
typed. The ::1 account is now created and granted alongside the other two.
Note the datadir guard means the first defect could not fire on a straightforward
re-run - stage 0 refuses a non-empty data directory before reaching the
bootstrap. It was still wrong, and reachable once the directory has been cleared
by hand, which is what the failure message tells operators to do.
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