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.

Reference outputs (iter-35 spike fixtures)

Pair	overall	cosine	categorical	jaccard
LEGAL × LEGAL (self)	1.0000	1.0000	1.0000	1.0000
LEGAL × SUPPORT	0.8296	0.9987	0.7500	0.2857
LEGAL × DEVOPS	0.5840	0.9734	0.0000	0.0000

Both invariants from ADR-152 §"Smallest demonstrable spike" hold:

1. similarity(X, X) === 1 exactly
2. similarity(LEGAL, DEVOPS) < similarity(LEGAL, SUPPORT) (vertical affinity)

Architectural constraint inheritance (ADR-150)

• Removable — pure-TS function, zero static @metaharness/* imports.
• Optional — no new dep in package.json.
• Graceful — malformed inputs emit { degraded: true, reason } with exit code 2; never throws.
• CI-gate — smoke step 17y locks the contract: module exports, spike fixtures reproduce, CLI dispatcher entry registered, MCP tool registered.

Usage

# File inputs
npx ruflo metaharness similarity --a a.json --b b.json

# Memory inputs (records persisted by oia-audit.mjs)
npx ruflo metaharness similarity --a-key harness-X --b-key harness-Y

# Per-dimension breakdown (used by ADR-151 §3.2 Recommender)
npx ruflo metaharness similarity --a a.json --b b.json --per-dimension

# Alert when too-dissimilar (used by ADR-151 §3.3 Drift Detection)
npx ruflo metaharness similarity --a a.json --b b.json --alert-below 0.5

Implementation

Production module: scripts/_similarity.mjs CLI skill: scripts/similarity.mjs MCP tool: mcp__plugin_ruflo-core_ruflo__metaharness_similarity (registered in v3/@claude-flow/cli/src/mcp-tools/metaharness-tools.ts) Spike anchor: scripts/_spike-similarity.mjs (regression suite — invariants locked here)