Decals: explosion scorch pool + cover damage-cracks + room-arena scars (Phase 1.5b bundle 2)

All procedural, client-only, observe-only in PresentationSystemGroup, zero
netcode surface (read existing replicated state). Shared FeedbackFx decal
primitives (scorch blob + crack star meshes + transparent decal material).
ScorchDecalSystem: static RequestScorch queue -> pooled fading discs
(mirrors DynamicLightSystem), wired from the barrel boom, reusable by the
geyser. CoverDamageSystem: crack accretion keyed on BlightClutter.Remaining
(Variant 4) + proximity-gated shatter-scorch. RoomDressingSystem: persistent
arena scars on a distinct hash sub-stream, torn down with dressing. Knobs in
DecalConfig. Cover cracks use decals (not URPMaterialPropertyBaseColor) because
the Synty prop shader is not Hybrid-Per-Instance.

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

Assets/_Project/Scripts/Client/Presentation/FeedbackFx.cs

@@ -109,5 +109,76 @@ namespace ProjectM.Client
             if (clip == null) return;
             AudioSource.PlayClipAtPoint(clip, pos, vol * GameVolume.Sfx);
         }
+
+        // ---- ground DECAL primitives (Bundle 2 — explosion scorch, cover cracks, room scars) ----
+
+        // Transparent unlit ground-decal material: Sprites/Default honours vertex colour × the per-renderer _Color
+        // MPB, blends alpha, is double-sided (Cull Off) and writes no depth (ZWrite Off) — so flat, overlapping
+        // ground decals never z-fight and never cast/receive shadows. Same shader family as the fuse disc.
+        public static Material MakeDecalMaterial(string name = "GroundDecal")
+        {
+            Shader sh = Shader.Find("Sprites/Default");
+            if (sh == null) sh = Shader.Find("Universal Render Pipeline/Particles/Unlit");
+            if (sh == null) sh = Shader.Find("Unlit/Transparent");
+            return new Material(sh) { name = name, renderQueue = 3000 }; // Transparent
+        }
+
+        // Irregular soft radial disc on the XZ plane (already flat — scale x/z, spin about Y): vertex alpha 1 at the
+        // centre fading to 0 at a JITTERED rim, so it reads as an organic scorch blob with NO hard rectangle edge
+        // (the feathered rim is what keeps it from ghosting over fog the way an opaque quad did). White vertex colour
+        // so the caller's material/MPB tint (dark char) shows through.
+        public static Mesh BuildScorchMesh(int segments = 24, float jitter = 0.3f, int seed = 1)
+        {
+            if (segments < 6) segments = 6;
+            var rng = new System.Random(seed * 6151 + 13);
+            var m = new Mesh { name = "ScorchDecal" };
+            var v = new Vector3[segments + 1];
+            var col = new Color[segments + 1];
+            var tris = new int[segments * 3];
+            v[0] = Vector3.zero;
+            col[0] = new Color(1f, 1f, 1f, 1f);
+            for (int i = 0; i < segments; i++)
+            {
+                float a = i / (float)segments * Mathf.PI * 2f;
+                float r = 1f - jitter * (float)rng.NextDouble();
+                v[i + 1] = new Vector3(Mathf.Cos(a) * r, 0f, Mathf.Sin(a) * r);
+                col[i + 1] = new Color(1f, 1f, 1f, 0f); // transparent feathered rim
+                int n = (i + 1) % segments;
+                tris[i * 3] = 0; tris[i * 3 + 1] = n + 1; tris[i * 3 + 2] = i + 1;
+            }
+            m.vertices = v; m.colors = col; m.triangles = tris;
+            m.RecalculateBounds();
+            return m;
+        }
+
+        // A jagged crack star on the XZ plane: `spokes` thin tapered triangles radiating from the centre at random
+        // angles/lengths, opaque at the base and feathered to nothing at the tip. Reads as surface cracking, visually
+        // distinct from the scorch blob. White vertex colour; caller tints dark and scales it to the piece.
+        public static Mesh BuildCrackMesh(int spokes = 3, int seed = 1)
+        {
+            if (spokes < 1) spokes = 1;
+            var rng = new System.Random(seed * 9277 + 5);
+            var m = new Mesh { name = "CrackDecal" };
+            var v = new Vector3[spokes * 3];
+            var col = new Color[spokes * 3];
+            var tris = new int[spokes * 3];
+            for (int s = 0; s < spokes; s++)
+            {
+                float a = (s / (float)spokes) * Mathf.PI * 2f + (float)(rng.NextDouble() - 0.5) * 1.2f;
+                float len = 0.6f + 0.4f * (float)rng.NextDouble();
+                float w = 0.06f + 0.05f * (float)rng.NextDouble();
+                var dir = new Vector3(Mathf.Cos(a), 0f, Mathf.Sin(a));
+                var perp = new Vector3(-dir.z, 0f, dir.x) * w;
+                int b = s * 3;
+                v[b] = perp; v[b + 1] = -perp; v[b + 2] = dir * len;
+                col[b] = new Color(1f, 1f, 1f, 1f);
+                col[b + 1] = new Color(1f, 1f, 1f, 1f);
+                col[b + 2] = new Color(1f, 1f, 1f, 0f); // feathered tip
+                tris[b] = b; tris[b + 1] = b + 2; tris[b + 2] = b + 1;
+            }
+            m.vertices = v; m.colors = col; m.triangles = tris;
+            m.RecalculateBounds();
+            return m;
+        }
     }
 }