feat(lang): 0.R5 - a reducer writes one state and may read others, declared between its state and the action

What only becomes known inside the drain - a value another reducer just set, the map in play - no longer
has to be faked into the action, so a verb that reads several systems while it changes one is a reducer
instead of an act handed its states. A second state to write is still refused, and the message says the
way out. examples/actions/reads.ludic; reseeded.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

changes/reducer-reads.md

@@ -0,0 +1,8 @@
+bump: minor
+type: feat
+**A reducer may read other states.** `reducer Wallet on Buy(w: mut Wallet, s: Shop, a: Buy)` writes
+its own state and reads the ones declared between it and the action, supplied by the drain like its
+own. What only becomes known inside the drain - a value another reducer just set, the map in play,
+where the save lives - no longer has to be faked into the action, and a verb that reads several
+systems while it changes one is a reducer instead of an act. A second state to WRITE is still
+refused, now with the way out in the message (`examples/actions/reads.ludic`).