Ship usage-rules.md in bb core (proposal 0007) #146

Summary

Ship a usage-rules.md in bb core, per proposal 0007 (open since 2026-01-12). There is currently no usage-rules.md anywhere in the ecosystem.

Why it matters

The usage_rules hex package is now standard across Ash/Spark-adjacent projects. For an ecosystem whose maintainer develops agent-first, this is the highest-leverage cheap win: it gives AI coding assistants authoritative, token-budget-conscious guidance on BB's patterns and the anti-patterns they commonly get wrong (DSL topology, the safety/disarm contract, BB.Math types, message naming conventions, BB.Process vs PubSub delivery).

Once published it's consumable via:

mix usage_rules.docs bb

Scope

Start with bb core (this issue). Proposal 0007 also covers bb_liveview, bb_kino, bb_reactor, bb_ik_dls, bb_ik_fabrik, and the four servo drivers — those can follow as per-package issues once the core file establishes the house style.

Reference

• Proposal: Proposal 0007: Usage Rules for Beam Bots Packages proposals#7
• Recommended structure: ~50-150 lines, references hexdocs/tutorials rather than duplicating, focuses on patterns and anti-patterns.