draw optimizations

client/world/renderer_query.go

@@ -57,22 +57,36 @@ func (w *World) collectCandidatesForTile(r Rect) []MapItem {
 	rowStart := w.worldToCellY(r.minY)
 	rowEnd := w.worldToCellY(r.maxY - 1)
 
-	seen := make(map[PrimitiveID]struct{})
-	result := make([]MapItem, 0)
+	// Start a new epoch for this tile dedupe.
+	w.candSeenResetIfOverflow()
+
+	// Reuse result buffer.
+	out := w.scratchCandidates[:0]
 
 	for row := rowStart; row <= rowEnd; row++ {
 		for col := colStart; col <= colEnd; col++ {
 			cell := w.grid[row][col]
 			for _, item := range cell {
 				id := item.ID()
-				if _, ok := seen[id]; ok {
+				if w.candSeenMark(id) {
 					continue
 				}
-				seen[id] = struct{}{}
-				result = append(result, item)
+				out = append(out, item)
 			}
 		}
 	}
 
-	return result
+	// Store back the reusable buffer (keep capacity).
+	w.scratchCandidates = out[:0]
+
+	// IMPORTANT:
+	// We must return a stable slice to the caller (plan stores it).
+	// Returning `out` directly would be overwritten on the next tile.
+	//
+	// So: copy out into a freshly allocated slice OR into a plan-level scratch pool.
+	// For Step 1 we keep correctness: allocate exactly once per tile.
+	// Step 3 will remove this allocation by making plan own a pooled backing store.
+	res := make([]MapItem, len(out))
+	copy(res, out)
+	return res
 }