capability

This fabric's role(s) and whether it can be attempted now. The single capability primitive — override this, not availability.

The default is a floor, not a verdict

Default: a roleless FabricAvailability.Unknown. This is the pre-connect surface a consuming app turns into actionable guidance — "Bluetooth is off", "can't reach the server" (#1530) — so a loom that has probed nothing must say "I cannot tell" rather than assert a confident FabricAvailability.Available the caller will then act on. It mirrors the floor Seam.capability took in #1712: an authoritative false negative is strictly worse than silence, and the two halves of one contract must not default in opposite directions (#1746).

Override it whenever you can answer. The question is "is this fabric attemptable on this runtime" — compiled in, permission granted, radio present — not "is the remote reachable", which is a live question a woven Seam's own capability answers. So three shapes of override are all correct, and the default is none of them:

• FabricAvailability.Available where it is established by construction — an in-memory loom, or an accept-side loom that acquires no OS resource and reaches no remote. Say in a comment why it is a fact, so the next reader can tell it from a guess.

• FabricAvailability.Unavailable where the answer is known and negative — a stub whose weave always throws on this target. (FabricAvailability's "simply absent" case is a fabric with no Loom at all on the target; a constructible stub is not that.)

• FabricAvailability.Unknown with a specific reason naming what was not established, where a real probe exists but has not been run.