Track myelinmesh consumption of ProbeMetrics / StabilityReport

[cursor]

Summary

myelinmesh v0.4 (askmy-stack/myelinmesh#21) plans usage-weighted Tool-Semantics change risk. Handoff contract lives in docs/downstream.md.

Acceptance criteria

• Keep docs/downstream.md aligned with exported ProbeMetrics / StabilityReport fields
• When myelinmesh lands an adapter, link the PR here and note any missing export fields
• If a new export field is required, split a dedicated tool-semantics API issue (do not bloating this tracker)
• Close this issue when myelinmesh can ingest metrics JSON without tool-semantics code changes — or convert to the follow-up API issue

Non-goals

• Implementing myelinmesh ranking logic in this repository