feat(senses): walkers slide round still things, and lines of sight are the world's to answer

- ludic.wildlife: WildlifeWorld.push / pushed_x / pushed_z (defaults change nothing); a ground
  walker's step is slid clear of a still thing with a body from its species' size and scale, and
  a step that gets nowhere turns away as the water does. Birds are not pushed; no dice added.
- ludic.npc: NpcWorld.push / pushed_x / pushed_z (a person 0.35 m round) in npc_walk, and
  NpcWorld.clear (default true), which npc_line_ok asks at 1 m so a detour does not cut a trunk.
- ludic.aim: AimView.clear replaces AimView.ground and the ground march; the pick asks the line
  a body's width short of where the ray enters the thing (aim_clear_at(t, back)), so a solid
  thing does not hide itself. probe.ludic (the ground-agreement probe) and AimView.dry are gone.
- ludic.photo: PhotoLens.clear replaces PhotoLens.ground, PhotoLens.trunk and the march.

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

packages/ludic.npc/tests/fake/index.ludic

@@ -11,6 +11,9 @@ export state NpcTestsFakeState {
   fk_on: []bool = null
   fk_born: int = 0
   fk_gone: int = 0
+  fk_trunk: bool = false         # a trunk 1 m round at (10, 0.3)
+  fk_out_x: float = 0.0
+  fk_out_z: float = 0.0
 }
 
 function fk_setup(npc_st: mut NpcState, npc_tests_fake_st: mut NpcTestsFakeState) -> void {
@@ -23,6 +26,7 @@ function fk_setup(npc_st: mut NpcState, npc_tests_fake_st: mut NpcTestsFakeState
   npc_tests_fake_st.fk_on = [true, false]
   npc_tests_fake_st.fk_born = 0
   npc_tests_fake_st.fk_gone = 0
+  npc_tests_fake_st.fk_trunk = false
   npc_clear(npc_st)
   npc_reset(npc_st)
   npc_seed(npc_st, 7)
@@ -61,3 +65,22 @@ function fk_count(npc_st: mut NpcState, what: int) -> int {
   for i in 0 .. len(fs) { if fs[i].what == what { n += 1 } }
   return n
 }
+
+# the trunk, when it stands: a body inside it is pushed straight out from its axis, and a line
+# passing within its radius is not clear
+function fk_push(npc_tests_fake_st: mut NpcTestsFakeState, x: float, z: float, r: float, y0: float, y1: float) -> bool {
+  let d = npc_d(x, z, 10.0, 0.3)
+  if not npc_tests_fake_st.fk_trunk or d > 1.0 + r or d < 0.0001 { return false }
+  npc_tests_fake_st.fk_out_x = 10.0 + (x - 10.0) / d * (1.0 + r)
+  npc_tests_fake_st.fk_out_z = 0.3 + (z - 0.3) / d * (1.0 + r)
+  return true
+}
+function fk_pushed_x(npc_tests_fake_st: NpcTestsFakeState) -> float { return npc_tests_fake_st.fk_out_x }
+function fk_pushed_z(npc_tests_fake_st: NpcTestsFakeState) -> float { return npc_tests_fake_st.fk_out_z }
+function fk_clear(npc_tests_fake_st: NpcTestsFakeState, ax: float, ay: float, az: float, bx: float, by: float, bz: float) -> bool {
+  if not npc_tests_fake_st.fk_trunk { return true }
+  let lx = bx - ax
+  let lz = bz - az
+  let t = Math.clamp(((10.0 - ax) * lx + (0.3 - az) * lz) / Math.max(lx * lx + lz * lz, 0.0001), 0.0, 1.0)
+  return npc_d(ax + lx * t, az + lz * t, 10.0, 0.3) > 1.0
+}

packages/ludic.npc/tests/npc_test.ludic

@@ -10,6 +10,10 @@ program NpcTest {
     ground: fn fk_ground
     water: fn fk_water
     allowed: fn fk_allowed
+    push: fn fk_push
+    pushed_x: fn fk_pushed_x
+    pushed_z: fn fk_pushed_z
+    clear: fn fk_clear
     hour: fn fk_hour_now
     day: fn fk_day_now
     players: fn fk_players
@@ -95,6 +99,21 @@ program NpcTest {
     expect_near(p.fx, 30.0, 0.01)
   }
 
+  test "a trunk in the way is walked round, and a line through it is not a clear walk" (npc_st: mut NpcState, npc_tests_fake_st: mut NpcTestsFakeState) {
+    let p = one(npc_st, npc_tests_fake_st, NPCK_HIKER)
+    npc_tests_fake_st.fk_trunk = true
+    expect(not npc_line_ok(0.0, 0.0, 20.0, 0.0))
+    expect(npc_line_ok(0.0, 5.0, 20.0, 5.0))
+    npc_go(npc_st, p, 20.0, 0.0, NPCA_SIT, 30.0)
+    var closest = 100.0
+    for k in 0 .. 600 {
+      npc_tick(npc_st, 0.05)
+      closest = Math.min(closest, npc_d(p.x, p.z, 10.0, 0.3))
+    }
+    expect(closest > 1.3)
+    expect_eq(p.act, NPCA_SIT)
+  }
+
   test "nobody walks into the lake" (npc_st: mut NpcState, npc_tests_fake_st: mut NpcTestsFakeState) {
     let p = one(npc_st, npc_tests_fake_st, NPCK_HIKER)
     npc_go(npc_st, p, -80.0, 0.0, NPCA_SIT, 30.0)