Hazard: Blight geyser — permanent periodic both-sides AoE (Phase 1.5b bundle 3)

Review-first netcode slice (design review wf_900e9965-8f0 -> 11 folded;
post-impl wf_5c8299f8-299 clean). A PERMANENT periodic telegraphed AoE in
Blight-biome rooms only; one new [GhostField] uint NextEruptTick.

- Geyser component + GeyserEruptSystem (server): inverted invalid-tick guard
  (a baked-0 tick must NEVER erupt -> lazy-stamps born-correct instead of the
  party-wiping per-tick barrage), inline both-sides gather (SourceNetworkId=-1),
  reschedule = now + period (never +=), never destroyed.
- GeyserTelegraphSystem (client): absolute-tick growing warning disc +
  erupt burst on the >0->=<0 crossing, latched per NextEruptTick + arm-guard
  (never edge-detects the replicated field -> no phantom on 0->stamp /
  relevancy re-entry). Reuses ScorchDecalSystem + DynamicLightSystem.
- Seeded in RoomFieldSystem (Blight-gated on plan.Biome, born-correct staggered
  stamp from live ServerTick), GeyserFieldSpawner + authoring wired into the
  Gameplay subscene. Geyser.prefab duplicated from ResourceNode (no collider).
- BuildDisc promoted to FeedbackFx (shared with the barrel fuse ring).
- 474/474 EditMode incl. the unstamped-storm regression; live no-storm end-to-end.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/_Project/Scripts/Simulation/Tuning.cs

@@ -121,6 +121,22 @@ namespace ProjectM.Simulation
         /// <summary>Detonation damage — hits LIVING enemies AND players alike (friendly fire = the bait mechanic).</summary>
         public const float BarrelExplodeDamage = 26f;
 
+        // ---- Blight geyser (Phase 1.5b bundle-3 hazard; periodic BOTH-SIDES AoE — see Geyser_Build_Spec) ----
+
+        /// <summary>Ticks between eruptions (~5 s @60). Server reschedules NextEruptTick = now + this each erupt
+        /// (never +=, per the review — anchored += catch-up-storms after a skip).</summary>
+        public const uint GeyserPeriodTicks = 300;
+
+        /// <summary>Telegraph window (ticks, ~1.3 s @60): the client grows the warning disc over the last this-many
+        /// ticks before an eruption (int so the client lead comparison stays signed).</summary>
+        public const int GeyserTelegraphTicks = 78;
+
+        /// <summary>Eruption AoE radius (world units, XZ) — hits LIVING players AND enemies (friendly fire = lure bait).</summary>
+        public const float GeyserEruptRadius = 3.0f;
+
+        /// <summary>Eruption damage per hit.</summary>
+        public const float GeyserEruptDamage = 22f;
+
         // ---- Expedition BOSS (a scaled Charger given a real kit by BossAISystem; server-only feel consts) ----
 
         /// <summary>Radial SLAM AoE radius (world units): a player inside this ring at wind-up elapse eats the hit