feat(economic): a device can publish, and a stranger can verify, which leaves its registered root commits

[cryptskii]

Summary

The generic economic-proof transport, first step of the locked chain. A device publishes which leaves its registered root commits; a stranger verifies them against a root it established itself.

validated post-transition tree  (the one the write set advanced)
        ↓                        root already registered at this position
one named position + root
        ↓
the externally citable leaves this transition wrote
        ↓
a 256-sibling inclusion path for each, from that same tree
        ↓
EconomicProofArtifactV1  ── frozen in the admit tx, delivered by the quorum sweep
        ↓
reader fetches by content address and RECOMPUTES against the root it named

Why nothing could be proven before

The register publishes the root at a position. It never published which leaves that root commits. EconomicSmt::siblings had exactly one production caller, inside the witness builder, and it published nothing. So the trader's 0x0026 (prove the owner's two vault reserves) and the owner's 0x0027 (prove the trader's settlement receipt) both needed material that did not exist. The existing trader settlement receipt does not substitute: it proves against the device tree under a different key derivation.

The three structural properties

property	how it is enforced
One snapshot	built from tree inside finish_admission — the same post-transition tree whose root was just registered, so no second read and no window for it to move. The root equality is stated, not assumed, and new re-derives every path before the bytes exist, so a mixed-snapshot artifact cannot be constructed
No self-assertion	no signature; verify_against takes the publisher, position and root the reader established independently and refuses anything else before recomputing. A locator makes an artifact findable, never valid
Keys are derived	the leaf key comes from the decoded state's class plus the publisher's coordinates, never supplied alongside the leaf

What gets published

Every admission publishes proof of the externally citable leaves its transition wrote: vault reserves and settlement receipts, the two classes an evidence type asks another device to verify. Balance and consumed-source leaves are excluded on purpose — nothing cites them, and each path costs 8 KiB, so carrying them would grow every admission to prove what no reader wants. That exclusion has its own mutation control.

The artifact is a post-admit artifact: frozen in the admit transaction and delivered by the existing quorum republish sweep, so it cannot reach the fleet before the root it names is registered.

Proof

check	result
a stranger with only coordinates, position and root recomputes every leaf and path, on a real admitted funded create fetched by content address	green
both reserve legs provable at the create's vault generation; no balance leaf carried	green
leaves and paths from two snapshots refused at construction and at reading	green
a tampered path, a repeated leaf, an amount the root does not commit	each refused
reading the same bytes at a position or root the reader did not establish	refused
decode is strict about shape and does not check inclusion, so shape alone is never evidence	green
mutation, per gate: verify_against root equality, check_inclusion recomputation, the producer self-check in new, the citable-leaf filter	each reddens only its own named test; restored checksum-verified
boards	workspace 74 binaries, 3964 passed / 0 failed / 17 ignored (dsm lib 1692/0, dsm_sdk lib 1813/0/7 ignored), exit 0; node 11 binaries, 276/0, exit 0; root make lint exit 0; frontend type-check 0, lint 0, jest 1101 passed; ci/production_safety_checks.sh PASS (pinned 1.98.0, incl. TLA+); scripts/ci_scan.sh PASS — all on tree stamp e0620f48fde5, identical before and after every run

Not in this PR

No evidence type consumes it yet. ReserveConsumptionEvidenceV1 and SettlementPaymentEvidenceV1 still carry their own bespoke leaf-and-path fields, and no routing advertisement carries a locator. Rewiring those to consume this object belongs with the 0x0026 producer, which is where a reader first needs to find one. Stated rather than left to be discovered.