Variable PROTOCOL_DEFAULT_CAPABILITIESConst

PROTOCOL_DEFAULT_CAPABILITIES: Readonly<Record<Protocol, Capabilities>> = ...

Default capability sets keyed by protocol. Callers that need a narrower surface for a specific source must intersect the default set themselves and pass the result on SourceDescriptor.capabilities; the built-in adapter constructors do not read service metadata today.

The matrix here mirrors the one in docs/protocol-capability-matrix.md. Update both together.