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>

selfhost/backend/emit_call.ludic

@@ -967,6 +967,7 @@ function emit_call(e: Node) -> Val {
   vis_check(fn2, name)
   state_inject_generated(e, fn2)                   # 0.S: a call the compiler wrote gets its states
   state_inject_runtime(e, fn2)                     # and a call into the runtime
+  if is_action_builtin(fn2.s) { state_inject(e, fn2) }   # 0.R: the action queue
   call_fill_defaults(e, fn2)                       # L11 - for code the checker does not walk
   reorder_named(e, param_labels(fn2))
   # evaluate args first (their IR is emitted before the call instruction), coercing
@@ -1119,6 +1120,6 @@ function emit_expr(e: Node) -> Val {
     let c = emit_bind(`icmp eq i32 {a.code}, 0`)
     return val(emit_bind(`zext i1 {c} to i32`), "bool")
   }
-  perr("cannot emit expression")
+  perr(`cannot emit expression (node kind {itoa(e.kind)})`)
   return val("0", "int")
 }