gc-viz

:EXPERIMENT: tool.gc-viz

Tri-color mark-sweep on a tiny heap. Two roots point into a live object graph; a two-node island (g ↔ h) and a lone i sit unreachable and will be swept.

Adapted from Peter Zhu's RubyConf 2026 talk Building the Next-Generation Garbage Collector in Ruby (Thu 11:15 B2). Ruby is moving to MMTk (memory management toolkit); tri-color mark is the primitive underneath.

This tool is the framework's canary: it ships at 50% rollout with a secondary exposure on tool.mutation. Half the users in the mutation arm see it; everyone else sees "gated off". See experiments for the shape.