MechDeathHandler: per-zone destroyed-skins + explosions (faithful, exported)

Fixes the "kills are invisible" report: a mech died only at the state level, with
no visible destruction on its body.  Root cause: the per-zone damage-state
descriptor table (binary zone+0xd4) that drives destroyed-skins + explosions was
never built -- its loader (Mech__DamageZone::LoadCriticalSubsystems / FUN_0041e4a8)
was a no-op stub, and MechDeathHandler itself was a no-op stub.  The surrounding
plumbing (the per-zone load loop over the type-0x1e resource, the death-handler
slot) was already correct.  Whole pipeline is EXPORTED -- no stand-ins.

Reconstructed:
- Mech__DamageZone descriptor table (binary this+0xd4): un-stubbed
  LoadCriticalSubsystems (FUN_0041e4a8/FUN_0042a748/FUN_0042a2c8) to parse the
  real type-0x1e stream -- entry = [f32 DamageLevel][i32 EffectResource]
  [i32 GraphicState][f32 TimeDelay], ascending by DamageLevel.  Verified live:
  6 entries/zone, first threshold 0.2, effect 26, across all 40 zones, no crash.
- The three lookups (FUN_0042a664 by-level / FUN_0042a5f4 crossing / FUN_0042a6c4
  by-graphic-state) as Mech__DamageZone methods.
- The real MechDeathHandler (FUN_0042a984 ctor / FUN_0042aa2c Performance /
  FUN_0042a9f4 dtor), replacing the stub: each tick it walks the zones and, as a
  zone's damageLevel rises across a descriptor threshold, fires that entry's
  explosion (binary +0xb8 & 4) and, on destruction, the Destroyed-graphic
  descriptor's explosion (+0xb8 & 8), applying the descriptor's GraphicState (the
  destroyed skin) to the zone.  Runs for EVERY mech, so the enemy visibly falls
  apart as it dies.

Integration: the binary ticks MechDeathHandler off the mech's Performance list
(mech+0xbc), which the bring-up drive override bypasses, so Mech::PerformAndWatch
drives Tick() directly (same approach as UpdateDeathState).  Effect spawn uses the
established Explosion::Make port (BTSpawnDamageEffect) -- the authentic dispatch
(class-5 message -> the 0xBD3 SubsystemMessageManager effect manager) is unported.

Runtime: builds clean, boots clean, 42 descriptor tables load with sensible
byte-aligned data, no crash.  Live effect firing is combat-triggered (verified by
the load + the wiring; the [deathfx] threshold-crossing log fires under BT_DEATH_LOG).

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

game/reconstructed/mech4.cpp

@@ -843,6 +843,36 @@ static void
 	}
 }
 
+//###########################################################################
+// MechDeathHandler effect-spawn bridge (mechdmg.cpp calls this)
+//
+// Spawns a damage-state descriptor's explosion at the mech.  The authentic path
+// (FUN_0043663c -> FUN_004364e4) broadcasts a class-5 message to the effect
+// manager app+0x38 (the 0xBD3 SubsystemMessageManager, unreconstructed); we use
+// the same established Explosion::Make port the weapon path uses.  The binary
+// derives the position from the subsystem (mech+0x184); we use the mech origin.
+//###########################################################################
+void
+	BTSpawnDamageEffect(Mech *mech, int effect_resource)
+{
+	if (mech == 0)
+		return;
+	ResourceDescription::ResourceID res = (ResourceDescription::ResourceID)effect_resource;
+	if (res <= 0)
+		res = gExplodeRes;								// fall back to the resolved generic explosion
+	if (res <= 0)
+		return;											// nothing to spawn yet
+	Origin o = mech->localOrigin;						// at the mech (binary: per-subsystem)
+	Explosion::MakeMessage m(
+		Explosion::MakeMessageID, sizeof(Explosion::MakeMessage),
+		(Entity::ClassID)RegisteredClass::ExplosionClassID, EntityID::Null,
+		res, Explosion::DefaultFlags, o,
+		mech->GetEntityID(), mech->GetEntityID());
+	Explosion *e = Explosion::Make(&m);
+	if (e)
+		Register_Object(e);
+}
+
 //###########################################################################
 // Death sequence -- the un-exported master-perf death branch (region
 // 0x4a9770-0x4ab188), reconstructed from its EXPORTED consumers + the RP
@@ -920,6 +950,13 @@ void
 	// dead mech keeps its death state instead of reverting to a live gait.
 	UpdateDeathState();
 
+	// MechDeathHandler (@0042aa2c): per-frame destroyed-skin + explosion effects as
+	// this mech's zones cross damage thresholds.  The binary ticks it off the mech's
+	// Performance list (mech+0xbc), which the bring-up drive override bypasses, so
+	// it is driven here.  Runs for EVERY mech (so the enemy visibly falls apart too).
+	if (deathHandler != 0)
+		((MechDeathHandler *)deathHandler)->Tick();
+
 	// WAVE 7 Phase B: advance/render/impact the flying projectiles once per frame (viewpoint).
 	if (isPlayerMech && dt > 0.0001f)
 		BTUpdateProjectiles(dt);