The renderGraph function was being called with nil instead of the loaded subgraph, causing a nil pointer dereference in computeDependencyCounts when iterating over subgraph.Dependencies. Changes: - Pass subgraph variable to renderGraph instead of nil - Add defensive nil check in computeDependencyCounts - Add test case for nil subgraph handling Fixes GH#657 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>