Capability System

Brain’s capability system is the unified substrate for everything the system can do.

Capability Registry

All capabilities are registered in a single ToolRegistry. Three producers feed into it:

1. Native backends — built-in capabilities declared by each backend module
2. MCP mounts — external MCP servers registered at runtime
3. Skill packs — (future) declarative capability bundles

Every capability has:

• ID — unique identifier
• Safety tier — Read / Write / Execute / Destructive / External
• Preconditions — what must be true for it to work
• When-to-use — guidance for the LLM
• Embedding — semantic descriptor for hybrid retrieval

Capability Discovery

The IntentRouter and CapabilityIndex route intents to registered capabilities using hybrid (cosine + keyword) scoring. A learned CapabilityFitnessStore tracks per-tool success/failure and provides a bounded tiebreaker in ranking.

Runtime Health

Capabilities carry runtime health state:

• Verified — working normally
• Degraded — dependency unavailable (e.g., embedder down for memory.store)
• BreakerOpen — circuit breaker tripped
• PreconditionFailed — missing prerequisite

The capability digest renders all health state in chat, and tools/list annotates per-tool status.