The natural moment to decide "15% from July" is while looking at July. The
control writes the same setRuleFrom action the history editor uses, so the two
surfaces cannot drift apart. A month where a version begins gets its own badge,
distinct from a one-month override, so a step in the numbers has a visible
cause; a month can carry both.
The editor is keyed on post and month so switching posts remounts it — without
that, React reuses the instance and useState keeps the previous post's values.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>