dispatch: capability constraints, and delivery over bearers that cannot answer #87

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dcharlot merged 1 commit from wai/constraints-and-unidirectional into main 2026-09-10 12:23:05 -04:00

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2026-09-10

Transaction Science

dispatch: capability constraints, and delivery over bearers that cannot answer ...

Two seams the tree could not express, both surfaced by the landscape survey.

CAPABILITY CONSTRAINTS. WAI dispatch treats support as binary — a sink either
claims a capability or does not. Real sinks support a codec TO A LEVEL: up to a
resolution, a frame rate, a bit depth, a profile. "This capability, but only to
4K60 10-bit, this profile" is the normal case and was unexpressible, so partial
support failed at DECODE time rather than SELECTION time, and rendition selection
had nothing to evaluate and deferred to a deployer policy the spec never states.

Ingests the constraint-set grammar and register pattern from AMWA's ratified
Receiver/Sender Capabilities work (BCP-004-01 / -02, v1.0.0) — ORed sets of
enum/min/max constraints over register-named parameters. Grammar and pattern
only: not the transport, not the discovery model, and explicitly NOT the
pre-flight negotiation framing, because capability-plus-budget binding before
execution is already owned by JCP and two mechanisms for one job is worse than
none.

The honest limit is stated in §3 rather than hidden: the ratified registers are
broadcast-essence-shaped and cover only WAI's conventional media families. There
are no entries for neural, quantum, world or haptic, and WAI must author those
itself — until it does, those capabilities remain unconstrained, which is the
true state rather than a pretended one.

UNIDIRECTIONAL DELIVERY. Three assumptions quietly presume the sink can talk
back: jwp-receipts assumes relay-chain linkage, targeting presumes the source
learns something about the sink, and pre-emption has no signer class because
nothing in WAI has needed to assert authority over a sink before. Terrestrial
broadcast, satellite and multicast object carriage break all three, and none is
repaired by defining a bearer.

  * Sink-evaluated predicates (§2): the object carries a condition the SINK
    evaluates against local state the source never learns, under a
    predicate-equivalence contract in the shape of state-feeds §3. The
    specifiable property is determinism and auditability, NOT enforcement —
    every sink receives every byte and can lie about its own state, and this
    text says so. The real claim is narrow and worth having: the source learns
    nothing, which is the dual of source-side targeting.
  * Authority and pre-emption (§3): pre-emption is the highest-authority
    instruction a media object can carry — it displaces what a person chose to
    watch — and today an object either lacks the field or has one anyone may
    set. Requires a sink-held trust anchor provisioned out of band; a trust
    anchor delivered over the bearer it authorises is not one. A valid signature
    establishes who signed, never that they were entitled to.
  * Detached receipts (§4): the deliverable is an honest profile, not a proof.
    Such receipts attest WHAT WAS TRANSMITTED, not what was received or
    rendered, and MUST declare the bearer unidirectional. No receipt can prove
    rendering over a bearer with no return path; what this prevents is the
    quieter error of a receipt saying "delivered" because a transmitter
    transmitted, on a link that cannot tell it whether anyone was listening.

Generalised from deployed national early-warning systems, which are where a sink
evaluating a condition the source never learns has had to work at scale.

Ingest queue items 10 and 11 (#80 §4.2, §4.3).

Co-Authored-By: Claude Opus 5 <[email protected]>

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