harness-similarity

Surfaces the production similarity function from scripts/_similarity.mjs as a callable skill. Use when an agent needs to:

• decide whether to fork an existing harness vs scaffold a new one
• rank candidate templates against a target repo's genome
• diff two harnesses produced by different teams to find duplicate work
• generate the confidence number that ADR-151 §3.2's Recommender wraps

Algorithm (from ADR-152 §Decision)

overall = 0.60·cosine + 0.25·categorical + 0.15·jaccard

• cosine — over a 9-dim numerical vector of normalized scorecard + genome dims
• categorical — fraction of 4 enum fields that match (repo_type, archetype, template, recommendedMode)
• jaccard — |A ∩ B| / |A ∪ B| over the agent_topology[] array

The 3-component design is load-bearing: numerical cosine alone is too coarse (the iter-35 spike showed LEGAL vs DEVOPS at cosine=0.97 despite being unrelated verticals). Categorical + jaccard pull the composite to the correct ordering.