World-pick targeting: 0x388 = whatever is downrange -- mech, terrain, or nothing (task #41)

User video evidence (lasers firing at nothing) + the colleague's
torso-locked report + the binary all reconcile into one model:

The boresight pick hits the WORLD, and the target slot mech+0x388 holds
whatever entity is downrange:
- enemy mech under the boresight -> aimed target (hull point -> STEP-6
  zone under the boresight, hotbox + lock ring, damage);
- else the TERRAIN downrange (BTGroundRayHit to 1200) -> the beam and
  missiles fire at the scenery ("firing at nothing", as in the pod
  videos), range caret reads the ground distance (authentic :5639), no
  damage;
- else (sky) -> no target, and the weapon's own double 0x388 gate
  refuses the discharge.

Binary evidence for non-mech targets: HudSimulation :5620 explicitly
handles a target WITHOUT damage zones (target->0x120 == 0) -- dead code
if only mechs were ever targeted. The pick is automatic every frame
(0x388: 11 reads / 0 direct stores in CODE).

Implementation: gBTTerrainEntity captured in MakeEntityRenderables
(Terrain::GetClassDerivations); mech4 pick = enemy PickRayHit else
ground ray -> terrain entity + ground point; damage/hotbox/lock only
for the mech pick; the task-40 enemy auto-converge REMOVED (facing away
now fires at the scenery, not magically at the enemy -- the user's
complaint). Verified all three states headless (BT_AIM 0,0 / .6,.5 /
0,-.8): aimed zone hits / terrain beams + 0 damage / no discharge.

Fourth (and evidence-complete) targeting model iteration; KB updated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

game/reconstructed/btl4vid.cpp

@@ -58,11 +58,19 @@
 #if !defined(APP_HPP)
 #	include <app.hpp>
 #endif
+#if !defined(TERRAIN_HPP)
+#	include <terrain.hpp>		// Terrain::GetClassDerivations (world-pick target, task #41)
+#endif
 
 #include <string.h>
 #include <math.h>
 #include <time.h>				// clock() -- the threat-trail ages (task #37)
 
+// WORLD-PICK TARGET (task #41): a live Terrain entity mech4 cites in
+// mech+0x388 when the boresight pick lands on the ground (the binary's target
+// slot holds non-mech world entities).  Captured in MakeEntityRenderables.
+Entity *gBTTerrainEntity = 0;
+
 
 //
 // Material-name substitution placeholders.  Mirrors RPL4VideoRenderer's
@@ -205,6 +213,19 @@ void
 			// `this_instance` in the CulturalIcon/Landmark arm has been fixed in
 			// L4VIDEO.cpp.
 			//
+			// WORLD-PICK TARGET support (task #41): the boresight pick can hit
+			// TERRAIN (the binary's target slot holds non-mech world entities --
+			// HudSimulation part_013.c:5620 explicitly handles a target without
+			// damage zones).  Capture a live Terrain entity for mech4's ground
+			// pick to cite in mech+0x388 (the pick POINT carries the geometry;
+			// which specific instance matters only to damage, which never routes
+			// to terrain).
+			{
+				extern Entity *gBTTerrainEntity;
+				if (gBTTerrainEntity == 0
+					&& entity->IsDerivedFrom(*Terrain::GetClassDerivations()))
+					gBTTerrainEntity = entity;
+			}
 			DPLRenderer::MakeEntityRenderables(
 				entity, model_resource, view_type);
 			break;