PAYLOAD_BUDGET

A fabric that names no frame ceiling — us.tractat.kuilt.core.Seam.maxPayloadBytes is null (see SeamConformanceSuite.payloadBudgetGap).

Unlike every other constant here this one is usually not a shortfall at all: null is the honest answer from a fabric with no wire limit to name (in-memory, and every relay fabric whose Connection publishes nothing), and the contract says so. It is declared rather than assumed because of the one case the suite structurally cannot test — a fabric that enforces a ceiling while publishing null, which proving would take a payload the size of the hidden limit. NwSeam is the known instance (16 MiB via encodeFrame), and it is why a declaration rather than an assertion is the right mechanism here: the declaration is what surfaced it.

A fabric in that position should point SeamConformanceSuite.payloadBudgetGap at its own blocking issue rather than at this constant, which says only "no ceiling to name". NwSeam does: it has a ceiling and refuses above it, but cannot yet promise it, because its receive path drops bytes under a multi-chunk burst (#2134). The doc section below tracks the rest.