wai/extensions/determinism-tiers.md

@@ -88,6 +88,12 @@ construction; the reverse does not hold.
 
 ## 4. Framing
 
+Both tiers here are **reproducibility** guarantees: a sink can check them from the
+bytes it received. A separate axis exists for media whose correctness is a
+downstream model's behaviour rather than a byte comparison — see
+[task-fidelity](task-fidelity.md), which is a sibling rather than a third tier
+precisely because such a claim is *not* sink-checkable from the bytes.
+
 WAI spans the spectrum rather than competing on one point of it. The
 `entropy-consistency` tier is the base learned-codec floor — the guarantee the
 field and the underlying standards already make — and WAI supports it directly.

wai/extensions/task-fidelity.md

@@ -0,0 +1,128 @@
+# WAI Extension: Task Fidelity
+
+> Status: Draft. Names the contract for media whose correctness is a **downstream
+> model's behaviour**, not a byte comparison — the class
+> [`determinism-tiers`](determinism-tiers.md) cannot express. Sibling to that
+> file, not a tier inside it: the tiers there are *reproducibility* guarantees a
+> sink can check from the bytes alone, and a task claim is not one.
+> No new wire format and no new receipt mechanism; a claim shape + an evidence
+> grading over §7, modelled on
+> [`energy-measurement`](energy-measurement.md)'s acquisition class.
+> Keywords **MUST**, **MUST NOT**, **SHOULD**, **MAY** are RFC 2119/8174.
+
+## 1. Why a second axis
+
+`determinism-tiers.md` answers one question: *does the sink reproduce the same
+bytes?* A growing class of coded media is not answering that question at all.
+Three independent arrivals, none of them WAI's:
+
+- **Video coding for machines.** ISO/IEC 23888-2 (MPEG-AI Part 2; **DIS**, FDIS
+  planned late 2026) codes video *and* descriptors extracted from it, jointly
+  optimised for bitrate and for machine-task performance after decoding. Its
+  fidelity target is a task's accuracy, not a pixel comparison.
+- **Feature coding for machines.** ISO/IEC 23888-4 (MPEG-AI Part 4; **CD**) codes
+  intermediate feature tensors from inside a machine-vision network — the origin
+  runs the first N layers, ships the tensor, the sink runs the remainder. **No
+  pixels are reconstructed at any point**, so there is no medium to hash.
+- **Vendor framing.** At least one vendor markets compression as safe for machine
+  consumption when the change it induces in a downstream model's behaviour is
+  statistically indistinguishable from the variance that model already tolerates.
+  No standards body, no designation — and the vendor's own material states the
+  industry lacks a shared framework for the claim, which is what makes the seam
+  worth naming rather than ceding.
+
+WAI today can register these as capabilities but cannot state what conformance
+means for them. `ReplicateClass::Behavioral` is a disclaimer, not a criterion.
+*Task-equivalent but not bit-equal* is unstateable, so an implementation either
+overclaims a reproducibility tier it does not meet or says nothing at all.
+
+**The distinction that makes this a separate file.** A reproducibility tier is
+checkable by the sink from the bytes it received. A task-fidelity claim is not:
+checking it requires a model, a corpus, and a test run. Listing the two together
+would blur the one property `determinism-tiers.md` currently keeps clean — that
+its tiers are verifiable without leaving the object.
+
+## 2. The claim
+
+A task-fidelity claim is a tuple, and it is meaningless with any element missing:
+
+| element | meaning |
+|---|---|
+| `model` | content address of the network the claim is about — the identity under which δ was observed |
+| `test` | content address of the task, corpus and metric the claim was measured under |
+| `tolerance` | τ — the behavioural change the claimant asserts is acceptable, in the metric `test` names |
+| `observed` | δ — the behavioural change actually measured under `test` |
+| `evidence` | the class in §3 |
+
+A claim asserts **δ ≤ τ under `test`, for `model`**. It asserts nothing about any
+other model, any other corpus, or any metric `test` does not name.
+
+- A claim **MUST** carry all five elements. A tolerance without an observation is
+  a target, not a claim, and **MUST NOT** be sealed as one.
+- `model` and `test` **MUST** be content addresses, not names. "Tested on a
+  standard detector" is unfalsifiable; a hash is not.
+- A claim **MUST NOT** be restated for a different model or corpus without a new
+  observation. Behavioural tolerance does not transfer by assertion.
+
+## 3. Evidence class (REQUIRED)
+
+What separates the rungs is **provenance and scope, not accuracy** — the same
+principle as `energy-measurement.md` §2, and for the same reason: a confidently
+formatted δ says nothing about whether anyone ran the test.
+
+| class | meaning | requires |
+|---|---|---|
+| `Measured` | δ was observed by running `test` against `model` on the stated corpus. | retained artifacts sufficient to re-run |
+| `Transferred` | δ was observed under a *different* model or corpus and is argued to carry over. | the source claim, and the argument, both named |
+| `Asserted` | δ is claimed without an observation. | — |
+
+- An implementation **MUST NOT** promote a claim's evidence class in transit, as
+  §2 of `energy-measurement.md` forbids for acquisition class.
+- A verifier that cannot resolve `model` and `test` **MUST** treat the claim as
+  `Asserted` regardless of the class stated, and **SHOULD** say so rather than
+  discard the claim silently.
+- `Transferred` **MUST NOT** be used to cross a modality or a task family. A
+  detector's tolerance is not a segmenter's.
+
+## 4. What the claim is, and is not
+
+- It is **not** a reproducibility tier, and **MUST NOT** be presented as one. A
+  capability carrying a task-fidelity claim **MUST NOT** thereby claim
+  `entropy-consistency` or `decode-equivalence`; those are separate assertions
+  about separate properties, and a capability may hold both, one, or neither.
+- It is **not** sink-checkable from the bytes. This is the defining limitation,
+  and stating it is the point: a receipt bearing a task-fidelity claim carries a
+  *graded assertion*, not a verification, and a relying party that treats it as
+  the latter has misread it.
+- It is **not** a quality metric. δ is behavioural change in a named downstream
+  task, not perceptual fidelity, and the two **MUST NOT** be reported in the same
+  field.
+- It does **not** license degradation elsewhere. A task-fidelity claim says
+  nothing about energy, and an object honouring a decoding-operation-reduction
+  hint is still bound by `determinism-tiers.md` §2.
+
+## 5. The split-computation case — named, not solved
+
+FCM makes the origin/sink **work partition** a negotiated wire parameter: the cut
+point N decides how much of the network each side runs. That breaks an assumption
+in `jwp-receipts.md`, where `joules_micro` is one `u64` for producing the object
+by one producer.
+
+A cut-point-aware receipt needs three things WAI does not have: joules before the
+cut, joules attributable after it, and a network-identity hash making the halves
+provably compose. The third is a carriage problem — the artifact a network
+identity names has no normative wire form in WAI today.
+
+This extension **does not** solve that. It records the gap so a task-fidelity
+claim over a split computation is not mistaken for a complete accounting: such a
+claim **MUST** state the cut point, and **MUST NOT** report a single joule figure
+as if one producer had done all the work.
+
+## 6. Framing
+
+Byte-comparability is becoming one fidelity contract among several rather than
+the only one. WAI's position is unchanged by that — it names contracts and grades
+the evidence behind them, and does not adjudicate which contract a domain should
+want. What would be wrong is silence: a ratified class of media arriving with a
+conformance notion the container cannot state, described instead in the vocabulary
+of a guarantee it does not make.