Two requests in one control. Tagging an existing cost is the refresh: the data
runs out, the owner enters the purchase, picks the plan, and the money is
booked while the cycle restarts from that date — because the anchor is the
latest charge. The data cap stops needing a flow of its own.
"+ New recurring cost" seeds a cost from the purchase being typed, and that
purchase becomes its first charge, so an anchored cost created this way is
anchored from the moment it exists. Both land in one mutate call, so a failure
cannot leave a cost with no first charge.
A calendar cost is offered only where its grid has a slot in the purchase's
month. sourceFor resolves that slot by LOOKUP (walking occurrencesOf and
matching the purchase's month) rather than by deriving it from monthOf alone —
everyNDays + calendar is a legal combination whose slots are specific days, so
a derived slot could name one that does not exist on the grid.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
