A force-directed call graph visualizes communication patterns among seven “flex” microservices, with circles representing system nodes and arrows showing directed edges. Node positions update dynamically via `d3.forceSimulation`, combining `forceLink`, `forceManyBody`, and `forceCenter`. Dragging nodes with the `d3.drag` API repositions them and restarts the simulation. The SVG renders labeled circles and arrowheads defined by a marker, with data from the `system_nodes` metadata.