The stage vocabulary for this team. Fetch this before you write
anything — every write that names a stage names it by key.

Why keys and not names. Stages are renameable per team, and teams
rename them: "Contract Executed" becomes "Application", "Funded" becomes
"Closed". The key never moves. Branch on key; show name to humans.

Purpose matters. A refinance has no Pre-Approved stage. Pass
purpose to get only the stages that apply, or read appliesToPurchase
and appliesToRefinance on each stage and decide yourself.

isTerminal marks the stages that end a loan's active life. A loan in
a terminal stage leaves the pipeline but stays readable.