fix: stagger particle lifecycle respawn

shaders/particle_gpu_validation.fragment.glsl

@@ -100,12 +100,16 @@ void main() {
             // Formal particles use GPU-resident lifecycle state. Each slot keeps
             // its age in B; A=0 marks this frame as a respawn so Trail does not
             // connect the retired position to the new randomized one.
-            bool respawn = u_mask.w > 0.5;
-            float age = respawn ? 0.0 : previous.b + u_pass.y;
+            bool initialSeed = u_mask.w > 0.5;
+            float lifecycleHash = particleHash(v_uv + vec2(17.31, 83.17));
+            float maxAge = u_marker.z * mix(0.75, 1.25, lifecycleHash);
+            float initialAgeHash = particleHash(v_uv + vec2(71.19, 29.47));
+            bool respawn = initialSeed;
+            float age = initialSeed ? initialAgeHash * maxAge : previous.b + u_pass.y;
             vec2 position = previous.rg;
             vec2 velocity;
             bool valid = !respawn && fieldVelocityAt(position, velocity);
-            if (!valid || age >= u_marker.z) {
+            if (!valid || age >= maxAge) {
                 respawn = true;
             }
 
@@ -139,7 +143,9 @@ void main() {
                     // frame; alpha still prevents an invalid visible segment.
                     position = respawnSeed(v_uv, previous.rg, 3.0);
                 }
-                age = 0.0;
+                if (!initialSeed) {
+                    age = 0.0;
+                }
             }
             fragColor = vec4(position, age, respawn ? 0.0 : 1.0);
             return;