Clear live trace when replacing G-code program

web/react/src/XyzacToolPreview.tsx

@@ -218,6 +218,27 @@ export function XyzacToolPreview({ visual, view = "p", zoom = 1, rotateMode = fa
         }
         clearLines(pathGroup);
         clearLines(liveGroup);
+        // A new PROGRAM_LOAD, including the transient empty snapshot while
+        // loading, starts a new live-trace epoch. Clear internal playback and
+        // history buffers as well as rendered geometry so the previous
+        // program's yellow/orange path cannot be painted again.
+        liveTrace = [];
+        playbackQueue = [];
+        playbackStart = 0;
+        queuedLastTick = -1;
+        renderedTick = state.tick;
+        renderedPose = state.livePose;
+        renderedJoints = state.joints;
+        renderedActiveSegment = state.activeSegmentId ?? 0;
+        renderedProgress = state.activeProgress;
+        paintedTick = renderedTick;
+        paintedPose = renderedPose;
+        paintedJoints = renderedJoints;
+        paintedActiveSegment = renderedActiveSegment;
+        paintedProgress = renderedProgress;
+        // Seed the new epoch without adding a visible history point. The
+        // first post-load motion delta will create the first live segment.
+        liveTick = renderedTick;
         bounds = fit(segments);
         // Long programs can contain thousands of linear blocks. Batch their
         // vertices so preview loading does not block the UI on one WebGL