confirmPassword() already checked the right account per guard, but the
session marker it stamped, auth.password_confirmed_at, was one flat
key shared by every guard. In shared-host mode the portal and console
guards keep their login in the same session, so confirming a
customer's portal password left the marker in place for an
operator-only gate too. One private method now computes the key for
all three callers so they cannot drift apart again.
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