# WAI Extension: Asset Provenance

> Status: Draft. Lever 4 — content-addressing + receipts + measured
> energy for content that cannot be reduced to instructions. WAI does not
> reconstruct the asset; it carries the opaque bytes and a signed,
> energy-accounted lineage. Conformance is **content-hash-equivalence**
> (recompute, compare) + signature validity. Reference impl: the
> `provenance` feature of `wai-rs`; tooling: `wai_prov`; live sink:
> wai.transaction.science/provenance.
Keywords **MUST**, **MUST NOT**, **SHOULD**, **MAY** are RFC 2119/8174.

## 1. Scope and model

A `wai.asset.provenance` object is **not a content capability** — it is a
JWP receipt profile *about* a carried asset, the way `jwp-receipts` is.
The asset itself declares an ordinary capability (`wai.image.jpeg`,
`wai.audio.flac`, …) and WAI carries it unchanged; the provenance receipt
adds three things the carried bytes do not have on their own:

1. **Tamper-evidence** — the asset is content-addressed
   ([`asset_content_hash`], BLAKE3 over the complete WAI envelope); a
   verifier recomputes it and compares.
2. **Lineage** — an ordered chain of processing **steps**, each binding
   its input and output content hashes, signed as one group.
3. **Energy accounting** — each step carries its measured/declared
   microjoules; the receipt totals them.

This is the "verifies whatever it carries" half of the thesis, for the
content the reconstruct half cannot touch. WAI never decodes the asset —
a sink hands the bytes to whatever native element renders that media.

In scope: the step model, the `AssetReceipt` group, the verification
obligations. Out of scope: a transport; a capture device; the asset's own
codec (it is opaque here).

## 2. The step

A `ProvStep` is one transformation in the asset's lineage:

| field | meaning |
|---|---|
| `op` | operation, e.g. `"origin.synthesize"`, `"encode.jpeg"`, `"derive.thumbnail"` |
| `input_hash` | content hash of the input (all-zero for an originating step) |
| `output_hash` | content hash of the output |
| `work` | exact deterministic work (pixels, samples) |
| `joules_micro` | measured/carried microjoules; `0` is the unmetered marker, never 0 J ([energy-measurement](energy-measurement.md) §2) |

Step content hash:
`BLAKE3("wai:prov-step\x01" || op_len | op | input | output | work | joules)`.

## 3. The receipt (`AssetReceipt`)

A JWP group: the asset's content hash is the identity, the per-step
hashes are the Merkle leaves (JWP's exact `moq-jwp:merkle-{leaf,node}`
domains), and one Ed25519 signature covers a profile payload carrying the
asset hash, the declared `media` + `capability`, the Merkle root, the
step chain, and the total joules. It chains across edits via
`parent_receipt_hash`, like the worlds / audio / haptic / splat receipts.

## 4. Conformance

> A conforming verifier MUST: (a) recompute the asset's content hash and
> require it equal the receipt's `asset_hash`; (b) require the step chain
> be linked — each step's `input_hash` equals the previous step's
> `output_hash`, and the final `output_hash` equals `asset_hash`; (c)
> recompute the Merkle root from the step hashes; (d) verify the Ed25519
> signature as SPEC §7 *Signatures* requires. A failure at any point is a failure — the asset is reported
> unverified, never "probably fine".

There is no tolerance parameter: the content hash matches or it does not.

## 5. Energy is measured, never invented

`joules_micro` per step is **carried** from a meter, exactly as the other
receipts carry it: `wai_prov` measures the real CPU energy of each encode
(IOReport via macmon, no sudo) and signs the figure. An unmetered step
carries the unmetered marker `0`, which a reader presents as unmetered and never
totals as zero joules. The receipt never derives energy it did not measure.

Each step's figure carries its acquisition class as an optional label
([energy-measurement](energy-measurement.md) §2.8), because the steps of one
lineage can be metered by different parties in different ways. A labelled step
binds its class into its leaf hash; a step with no label keeps its legacy leaf
and its figure is unlabelled. `wai_prov` labels each encode it measures
`OnChipCounter`, with its declared uncertainty, and records an encode whose
measurement fails the §4 ratio or the power reader's liveness (§3.1) as
unmetered, and writes a measurement report for each step it measured
(energy-measurement §6). With `--carry` it measures nothing: it carries each
figure, and its label, from an earlier receipt for the same lineage, which must
verify and whose steps must have the same operations, hashes and work, and writes
no report. `total_joules_micro` carries no class of its own, and a
total over steps that include an unmetered one covers only the measured steps
(`Partial`).

## Appendix

The reconstruct classes prove WAI can ship a world, a sound, a body, a
volume as instructions and have every sink rebuild them identically.
Provenance proves the complement: for the photograph that is just a
photograph, WAI still adds something a bare file cannot — a tamper-evident
identity, a signed lineage, and an honest energy ledger — without ever
pretending to understand the pixels. Carries whatever it can reconstruct;
verifies whatever it carries.

[`asset_content_hash`]: ../wai-rs/src/world/mod.rs