Function cronStep

Does ONE unit of cron work and hands back the next cursor.

Shaped as a pure-ish function of (cursor, deps) so the caller keeps ownership of persistence: the cursor goes to cfw_meta or ctx.storage.put(), whichever the Durable Object already uses, and neither choice leaks in here. That is also what makes the chain testable without a Durable Object at all.

mayContinue is the CPU constraint expressed as data. A sql unit costs microseconds, so the caller may run another in the same invocation; a php unit enters the interpreter and must be the last thing that invocation does. This is the same trade fillBatchSize()/fillBatchWallMs() make in src/site-do.js -- batch to amortise the setAlarm() row write, but never batch across a render.

result is the unit's own ledger or reply and its shape depends on the unit, so it is declared as an index signature rather than object -- a bare object makes every field unreadable to a typed caller, which is what the ported specs hit.