Is my community login the same as my app account?
Not yet. They are separate accounts today, and joining them up is planned work rather than a thing you can do now.
Not at the moment. The account you create on these community boards is separate from your CruiseChattr app account, and signing in to one does not sign you in to the other.
That is a deliberate staging point rather than an oversight. The plan on record is that a community account becomes your CruiseChattr account, so that your handle is the same everywhere and you only have one password to remember. The groundwork for it is already in place.
What is holding it up is worth being straight about: handles in the app are not yet guaranteed unique across every kind of account, and family members do not have handles at all. Joining the two systems before that is sorted would mean deciding, badly and automatically, who gets to keep which name. That is not a decision to make on someone's behalf.
Until then: two accounts. When it changes, you will not have to migrate anything.
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