capability

The base fabric's verdict, verbatim. Multiplexing changes how many logical sessions share a link — not which medium carries it, nor whether that medium is usable on this runtime — so the base's capability is this loom's capability, in both halves.

Inheriting Loom's default would be strictly worse than an un-established guess: it would discard a verdict already established one layer down. A base that knows its dylib will not load reports FabricAvailability.Unavailable, and wrapping it must not launder that into a confident Available. The TransportCapability.roles half matters just as much — it is read pre-weave by CompositeLoom.weave and CompositeSeam.attachDesiredPly and captured onto the ply for the composite's role rollup, so a muxed ply defaulting to emptySet() silently under-reports what the composite can do (#1936).

Deliberately not generation-aware: Loom.capability is the pre-connect surface, answered before and independently of any weave. The live per-session view is Seam.capability.