feat(lang): 0.R1 - actions and reducers

action Name { fields } is a typed record; reducer State on Action(s: mut State, a: Action) { ... }
in the module that owns the state takes exactly that state and the action (a second state is
refused); dispatch Action { fields } queues one from anywhere, the queue supplied by the runtime.
The queue is drained at the end of every phase of the frame loop, after every phase of ludic.base's
core_tick_all, and by drain_actions(): in dispatch order, each action's reducers in the order of
their states' names, an action a reducer dispatches queued behind, a queue still growing after 64
rounds stopped with the action named. Examples actions/pack, phases, runaway; rejects for a second
state, a reducer on a non-action and an unknown dispatch; ludic.base's actions_test; LANGUAGE.md.

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

changes/actions.md

@@ -0,0 +1,11 @@
+bump: minor
+type: feature
+**Actions and reducers.** `action PickUp { item: int }` is a typed record of something that
+happened; `reducer Bag on PickUp(b: mut Bag, a: PickUp) { ... }`, in the module that owns the state,
+says what it means for that one state - a reducer takes exactly its state and the action, and a
+second state is refused; `dispatch PickUp { item: 7 }` queues one from anywhere. The queue is drained
+at the end of every phase of the frame loop, after every phase of ludic.base's `core_tick_all`, and
+where a program calls `drain_actions()`: in dispatch order, each action's reducers in the order of
+their states' names, an action a reducer dispatches queued behind (a queue still growing after 64
+rounds stops the program, naming the action). `ludic deps` reports `widest_function` - the most
+states any function or entry point of the program takes - and `--check` ratchets it.