Hazard: exploding barrels — fused explosive clutter, friendly-fire bait

Phase 1.5 environmental hazard v1 (design-review wf_2cb10454-fdf: 13
findings confirmed + folded; Build Spec in the vault). ~25% of room
clutter seeds as EXPLOSIVE (Variant 3 on the existing replicated byte
- zero new GhostFields/prefabs/RPCs).

The FUSE is the review's fold - one mechanism closes both HIGHs:
- Pop sites (projectile sweep + isServer-gated melee harvest) do NOT
  destroy an explosive: they zero the replicated Remaining + add a
  server-only BarrelFuse (~36 ticks). The client sees Remaining=0 on a
  still-alive barrel across snapshots -> unambiguous fuse cue, and
  booms at despawn ONLY when cached Remaining<=0 - a teardown despawn
  carries Remaining>0, so portal-advance teardowns can never fire
  false booms (HIGH #1).
- HazardExplosionSystem (server, plain group, presence-gated on
  BarrelFuse, never lifecycle-gated) detonates at ExplodeTick: radius
  damage to LIVING enemies AND players (boss-slam player filter
  verbatim; friendly fire = the bait mechanic), SourceTick stamped at
  detonation = the authoring moment (HIGH #2: the authored-tick
  contract dash i-frames negate against), SourceNetworkId=-1 (the
  environment convention - a player id would consume Charger
  whiff-punish windows). Fuse rides the RoomTag'd barrel -> teardown
  cleans lit barrels free.
- Lit barrels are unhittable at both snapshot sites (no double-pop).
- Client: WorldFeedback caches Variant -> boom-vs-puff split (big
  burst + light flash + boom SFX vs the old puff); DynamicLightSystem
  gives Variant-3 barrels a red danger glow that STROBES once fused.

Verified: 470/470 EditMode (4 new: fused pop instead of destroy +
unhittable, both-sides damage w/ -1 source + authored tick, dead-player
+ radius filters, unelapsed-fuse inert); live smoke - seeded 3/8
explosive, real-sweep pop, CLIENT observed the fuse cue on the live
ghost, pinned bait enemy took exactly 26 (30->4), walk-out escape
confirmed; console clean.

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

Assets/_Project/Scripts/Simulation/Combat/BarrelFuse.cs

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+using Unity.Entities;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// Server-only lit-fuse marker on an EXPLOSIVE clutter barrel (BlightClutter.Variant==3) that has been
+    /// popped: the pop sites zero the barrel's replicated Remaining (the client's unambiguous fuse cue —
+    /// a still-alive barrel with Remaining==0 can only mean "about to blow"; a room-teardown despawn still
+    /// carries Remaining&gt;0, so the client's boom-vs-puff choice at despawn cannot misfire) and add this
+    /// component instead of destroying. HazardExplosionSystem detonates when <see cref="ExplodeTick"/>
+    /// elapses: radius damage to LIVING enemies AND players (friendly fire = the bait mechanic), then the
+    /// single DestroyEntity. Never replicated; the fuse rides the RoomTag'd barrel, so room teardown / the
+    /// Staging sweep clean lit barrels for free (no orphaned-event lifecycle).
+    /// </summary>
+    public struct BarrelFuse : IComponentData
+    {
+        /// <summary>Server tick the barrel detonates (via TickUtil.NonZero — 0 never means "ready").</summary>
+        public uint ExplodeTick;
+    }
+}

Assets/_Project/Scripts/Simulation/Combat/BarrelFuse.cs.meta

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