A status change is a guarded business event, not a field write.
Name it
Say what this problem really is, professionally — the concept + when it bites. practice the framing →
Explain it out loud
Say it in your own words — but hit these: finite state machine · allowed transitions · illegal · guard · one transaction · audit
checking microphone…
Code it (7-step rhythm, narrate)
Clarify → approach → data model → narrate → edge → test → tradeoff. AI off. Lab: Offer / Transaction FSM →
Edge cases — say + handle each
Say the trade-off
“It's more ceremony than a status field and an if-statement, but illegal transitions become impossible instead of a 2am incident.”
checking microphone…
Answer the follow-up
How do you handle a transition with a side effect like an email or a charge?
Catch the classic bug
Spot the wrong implementation in <60s. open the bug drill →