Progressive rollouts explained

1. Publish the flag with code that can handle both branches.
2. Add a targeting rule. Use a segment or no predicate.
3. Set rolloutPercent to a small number and publish.
4. Check a known user with server evaluate. The bucket is stable for project, environment, flag key, targeting key, and salt.
5. Raise the percent in a later publish. Users already inside stay inside while the salt is unchanged, because the test is bucket < percent * 100.

The percent does not increase on a timer. scheduleStart and scheduleEnd only bound when the rule is eligible. Changing the salt reshuffles assignments.