Combat visible + killable: Wword root-cause fix, .PFX effect layer, RemakeEntity swap

The 'can't kill the enemy / no visible damage' cluster, root-caused and fixed
faithfully:

- STEP-6 unaimed path was INERT: the cylinder table was 'cached' at Wword(0x111)
  -- the recon ABSORBER bank (stores nothing, reads 0) -- so every unaimed hit
  silently no-op'd.  Promoted to the named member Mech::damageLookupTable
  (binary this[0x111], was mislabeled ammoExpended).  New gotcha class recorded
  (reconstruction-gotchas §2) + sweep; 2 dead multiplayer branches logged.

- Fire path migrated off the stale vital-zone aim onto the completed STEP-6
  unaimed dispatch (zone=-1 + beam entry point -> cylinder resolves the
  exterior zone).  No more invisible 1-shot kills; death via the authentic
  cascade (~14 center-mass hits).  Wreck stays TARGETED on kill (beams stop on
  it); scoring latches off.

- SendSubsystemDamage AV fixed: unbound critical-subsystem plug guard (43
  unbound plugs/mech logged as an open question -- the binding itself is a gap).

- RemakeEntity (render damage swap): the 1996 render state machine's missing
  Remake state, reconstructed as an in-place SetDrawObj mesh swap keyed by each
  segment's damage-zone graphic state (tree dtor doesn't cascade -> never
  rebuild).  Destroyed arms/guns visibly wreck (the only variants the RES
  registers).

- BT .PFX particle layer (L4VIDEO.cpp): the 1995 explosion/damage effect layer,
  unported since 2007 (DPLIndependantEffect/ReadPSFX/ExplosionScripts all
  stubs).  Parses the authentic VIDEO/*.PFX definitions via the [pfx_day]
  psfxN mapping; premultiplied blending renders BOTH families from the same
  data (additive-style fire + occluding smoke -- DDAM2 is 30% grey, DDTHSMK
  ramps negative: impossible additively); depth-sorted billboards with a
  radial-masked grit sprite; impact-frame orientation (.PFX offsets are
  authored mech-local, -Z = out of the struck armor toward the shooter) for
  weapon hits AND damage bands (via lastInflictingID, now maintained -- was
  declared but never written).  Both effect-number encodings route (raw dpl
  <100 + WinTesla 1000+slot carried by the band resources).  Death fires the
  authentic dnboom (7) + ddthsmk smoke plume (1).

- Effects anchor at the impact point / damaged zone's segment, not the mech
  origin (no more fire at the feet).

- Dev force-input gates BT_AUTOFIRE / BT_AUTODRIVE for headless fire-chain
  verification; BT_PFX_ADD=1 flips the particle blend for A/B.

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

game/reconstructed/mechdmg.cpp

@@ -575,6 +575,24 @@ void
 	{
 		Subsystem        *s  = criticalSubsystems[i]->subsystemPlug.Resolve();	// +4
 		MechCriticalSubsystem *cs = criticalSubsystems[i];
+
+		// UNBOUND-PLUG GUARD.  Resolve() (FUN_00417ab4) returns the subsystem bound
+		// to the DZSlot, or 0 if plug+8 was never wired.  In the 1995 binary every
+		// critical subsystem exists and is bound, so it dereferences s with no check.
+		// In this reconstruction a critical subsystem can be UNBOUND (its type is not
+		// yet built, or its slot never connected), leaving s == 0 -> the original
+		// code AV'd here (mov [edx+0xc], edx=0) as soon as a zone with such a plug was
+		// destroyed.  Skip the unbound entry rather than crash; log it so the missing
+		// binding can be tracked.  NOT a behavioural stand-in: a bound plug takes the
+		// authentic path below unchanged.  [T3 -- see open-questions: crit-subsys binding]
+		if (s == 0)
+		{
+			if (getenv("BT_DEATH_LOG"))
+				DEBUG_STREAM << "[deathfx] crit-subsys " << i << "/" << criticalSubsystemCount
+					<< " UNBOUND (plug not wired) -- skipped\n" << std::flush;
+			continue;
+		}
+
 		Mech__DamageZone *zone = (Mech__DamageZone *)((SubProxy2 *)s)->damageZone;	// subsystem[0x38] @0xE0
 
 		zone->damageLevel += (cs->damagePercentage - cs->damagePercentageUsed);
@@ -911,7 +929,12 @@ void
 // live): spawns the descriptor's explosion resource at the mech.  The authentic
 // path dispatches a class-5 message to the effect manager (app+0x38 -> the 0xBD3
 // SubsystemMessageManager, unreconstructed); we use the established Explosion port.
-extern void BTSpawnDamageEffect(Mech *mech, int effect_resource);
+extern void BTSpawnDamageEffect(Mech *mech, int effect_resource, int segment_index);
+
+// Render bridge (btl4vid.cpp): swap a mech's wrecked segment meshes onto its
+// already-built render tree when a damage zone's graphic state changes (the
+// unported "RemakeEntity" render state).  Entity* param -> Mech* binds fine.
+extern void BTRemakeMechModel(Entity *entity);
 
 MechDeathHandler::MechDeathHandler(Mech *mech)			// @0042a984
 	: owner(mech)
@@ -960,8 +983,27 @@ void
 		}
 		if (d != 0)
 		{
-			BTSpawnDamageEffect(owner, d->effectResource);	// explosion at the zone
-			zone->ApplyDamageGraphicState(d->graphicState);	// destroyed skin
+			BTSpawnDamageEffect(owner, d->effectResource,	// explosion AT the zone's
+					zone->segmentIndex);					// segment (world position)
+			zone->ApplyDamageGraphicState(d->graphicState);	// destroyed skin (graphic state)
+			// A graphic-state change means the segment's MODEL changed (intact ->
+			// destroyed variant, keyed by GetVideoObjectName(skl, gstate)).  Fire
+			// the engine's model-rebuild flag so the renderer re-runs
+			// MakeMechRenderables and loads the destroyed segment geometry -- the
+			// same mechanism CulturalIcons use to visibly deform on damage
+			// (CULTURAL.cpp:91; EXPTBL.cpp:549 does this per zone in the engine's
+			// ExplosionTable).  Without this the tree stays as built at spawn (intact).
+			// The render's "RemakeEntity" state (which consumes this flag) was
+				// NOT ported -- the mech tree is built once at spawn -- so we drive the
+				// equivalent directly: set the flag (authentic signal; also flags the
+				// zone for net damage replication) AND call the render bridge, which
+				// swaps the wrecked segment mesh onto the already-built tree in place.
+				// The single-threaded frame loop makes the immediate swap safe.
+				if (d->graphicState != DamageZone::ExistsGraphicState)
+				{
+					owner->ForceUpdate(Entity::DamageZoneUpdateModelFlag);
+					BTRemakeMechModel(owner);			// RemakeEntity: swap in the destroyed mesh
+				}
 			if (getenv("BT_DEATH_LOG"))
 				DEBUG_STREAM << "[deathfx] zone " << i << " level " << level
 					<< " -> effect " << d->effectResource << " gstate " << d->graphicState