fix: suppress frame:ready until full LOD update after param changes (#8602)

When gsplat params change (e.g. splatBudget), the frame:ready event could
report ready=true before the LOD system had fully reacted — especially with
GPU sorting where sortedVersion catches up in the same frame. This made it
impossible for consumers to reliably detect the not-ready→ready transition.

Add _awaitingLodUpdate flag that suppresses ready=true until a fullUpdate
cycle runs (which polls load completions and re-evaluates LODs). The flag
is only set when octree instances exist, so non-streaming scenarios are
unaffected.

Co-authored-by: Martin Valigursky <mvaligursky@snapchat.com>

Author: mvaligursky

src/scene/gsplat-unified/gsplat-manager.js

@@ -202,6 +202,15 @@ class GSplatManager {
     /** @type {number} */
     sortedVersion = 0;
 
+    /**
+     * When true, suppresses ready=true in frame:ready until a fullUpdate cycle runs.
+     * Only set when octreeInstances exist and params change (dirty).
+     *
+     * @type {boolean}
+     * @private
+     */
+    _awaitingLodUpdate = false;
+
     /**
      * Cached work buffer format version for detecting extra stream changes.
      *
@@ -1161,7 +1170,7 @@ class GSplatManager {
      * Fires the frame:ready event with current sorting and loading state.
      */
     fireFrameReadyEvent() {
-        const ready = this.sortedVersion === this.lastWorldStateVersion;
+        const ready = this.sortedVersion === this.lastWorldStateVersion && !this._awaitingLodUpdate;
 
         // Count total pending loads from octree instances (including environment)
         let loadingCount = 0;
@@ -1372,6 +1381,8 @@ class GSplatManager {
 
             // check if camera has moved/rotated enough to require LOD update
             cameraMovedOrRotatedForLod = this.testCameraMovedForLod();
+
+            this._awaitingLodUpdate = false;
         }
 
         // check if camera has moved enough to require re-sorting
@@ -1404,6 +1415,12 @@ class GSplatManager {
             // colorization) is refreshed immediately instead of trickling in over time.
             this._workBufferRebuildRequired = true;
             this.sortNeeded = true;
+
+            // Suppress ready=true in frame:ready until a fullUpdate cycle runs, so
+            // consumers can reliably detect the not-ready→ready transition after param changes.
+            if (this.octreeInstances.size > 0) {
+                this._awaitingLodUpdate = true;
+            }
         }
 
         // when camera or octree need LOD evaluated, or params are dirty, or resources completed, or new instances added