* docs: third-party-product plugins ship standalone, not into core tree
Generalizes the closed-set memory-provider policy to any plugin that
integrates someone else's product/project (observability backends,
vendor SaaS, analytics dashboards, paid-service tie-ins). These create
an open-ended maintenance burden on us for backends we don't own, so
they ship as standalone plugin repos installed into ~/.hermes/plugins/
and are promoted in #plugins-skills-and-skins — not merged into core.
- AGENTS.md: new 'what we don't want' bullet + generalized policy note
beside the memory-provider closed-set rule
- CONTRIBUTING.md: new 'Third-Party Product Integrations' section
- build-a-hermes-plugin.md: caution callout at the top of the guide
It's a coupling decision, not a quality bar — a plugin can clear review
and still be a close.
* docs: add infographic for standalone-plugin policy
