feat(input): action maps + deterministic record/replay (#7)

The two ideas the input revamp leads with, built in Ludic over the
single-key poll every target already provides:

- Action maps: gameplay reads named actions, not physical keys, so keys
  are rebindable and a scheme is data. Input.bind(action, key),
  Input.down/pressed(action), Input.rebind(action, from, to).
- Deterministic record/replay: Input.poll() is the one per-frame input
  read; Input.record() captures the key each frame and Input.replay()
  feeds the tape back, so a run reproduces exactly — the seed of lockstep
  netcode. "Read input" and "read a recorded snapshot" are the same call.

runtime/native/input.ludic (spliced when the new Input.* methods are used;
pulls in core.ludic for rt_poll). emit_ns_call routes the methods to the
@fn_input_* runtime; parse.ludic gates the splice. Seven docs/language
pages; worked example + regression examples/library/input_actions.ludic
(1 0 1 1 0 1 0). Full suite 75 passed, self-host fixpoint intact, no golden
drift. The device layer (multi-key held, gamepads, touch, analog) needs a
platform key-state backend and is tracked separately.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/backend/emit_call.ludic

@@ -177,6 +177,15 @@ function emit_ns_call(ns: pointer, meth: pointer, e: Node) -> Val {
   }
   if (ns == "Input") {
     if (meth == "key") { bare = "key" }
+    # action maps + deterministic record/replay (#7) — spliced runtime in
+    # runtime/native/input.ludic, reached as ordinary @fn_input_* calls.
+    if (meth == "bind")    { bare = "input_bind" }
+    if (meth == "rebind")  { bare = "input_rebind" }
+    if (meth == "poll")    { bare = "input_poll" }
+    if (meth == "down")    { bare = "input_down" }
+    if (meth == "pressed") { bare = "input_pressed" }
+    if (meth == "record")  { bare = "input_record" }
+    if (meth == "replay")  { bare = "input_replay" }
   }
   # Phase 3: the bare reflection / networking / process builtins, namespaced.
   # Each is a pure alias — the callee is rewritten to the bare name below.

selfhost/frontend/parse.ludic

@@ -180,6 +180,9 @@ function p_postfix() -> Node {
       if e.a.kind == E_ID and e.a.s == "Light" { g_uses_light = true }   # splice the 2D light-accumulation pass on demand
       if e.a.kind == E_ID and (e.a.s == "Value" or e.a.s == "Json") { g_uses_value = true }   # splice the value tree + JSON on demand (#44)
       if e.a.kind == E_ID and e.a.s == "Reflect" and (e.s == "serialize" or e.s == "apply") { g_uses_value = true;  g_uses_reflect_io = true }   # Reflect.serialize/apply -> value tree + world table
+      # Input.* action-map / record-replay methods (#7) -> splice input.ludic.
+      # Input.key stays bare (no runtime), so gate on the new methods only.
+      if e.a.kind == E_ID and e.a.s == "Input" and (e.s == "bind" or e.s == "rebind" or e.s == "poll" or e.s == "down" or e.s == "pressed" or e.s == "record" or e.s == "replay") { g_uses_input = true }
     }
     else { if is_op("[") { pi = pi + 1; let lo = expr()
         if is_op("..") { pi = pi + 1; let sl = node(E_SLICE); sl.a = e; sl.b = lo; sl.c = expr(); eat_op("]"); e = sl }   # s[a..b] substring
@@ -408,6 +411,7 @@ var g_uses_light: bool = false    # a program mentioned Light.* -> splice the 2D
 var g_uses_value: bool = false    # Value.*/Json.*/Reflect.serialize -> splice the value tree + JSON (#44)
 var g_uses_reflect_io: bool = false  # Reflect.serialize/apply -> splice the reflection serializer
 var g_uses_esys: bool = false     # an engine-owned system component (SpriteAnim/Motion/Light2D) is declared -> splice systems.ludic + force the reflection ABI
+var g_uses_input: bool = false    # a program used Input.bind/down/poll/… (action maps + record/replay) -> splice input.ludic
 
 function already_loaded(full: pointer) -> bool {
   var i = 0
@@ -610,6 +614,15 @@ function maybe_splice_runtime() -> void {
   # (emit_engine_systems_for_phase). The systems read/write components through the
   # reflection ABI, so g_uses_esys also force-emits the world table (emit_decl).
   # Light2D/Occluder additionally consume the 2D light pass, so pull it in too.
+  # Input.* action maps + record/replay (#7): splice input.ludic. It reads the
+  # live key through rt_poll (core.ludic), so pull the runtime in even for a
+  # program with no ECS (do_import dedupes when a game already linked core).
+  if g_uses_input {
+    cur_dir = ""
+    do_import("runtime/native/core.ludic")
+    do_import("runtime/native/input.ludic")
+    cur_dir = saved
+  }
   if uses_engine_systems() {
     g_uses_esys = true
     cur_dir = ""
@@ -648,6 +661,7 @@ function parse_program() -> void {
   g_uses_query = false
   g_uses_reflect = false
   g_uses_esys = false
+  g_uses_input = false
   g_uses_light = false
   g_uses_value = false
   g_uses_reflect_io = false