Agent detection was walking ad-hoc registry shapes and could miss agents exposed only through the canonical registry helpers. This makes getAgentDefinition and resolveAgent the preferred lookup path, uses AGENT_IDS/getAgentDefinitions for default scans, and keeps unknown ids as structured unavailable results without executing anything.

Constraint: User limited edits to src/agents/detect.js and test/agents-detect.test.js

Rejected: Probing unknown ids as shell commands | would execute untrusted command names and hide registry drift

Confidence: high

Scope-risk: narrow

Tested: node --test test/agents-detect.test.js