Example of "Physical or digital gold: simple insurance on Ergo"

[kushti]

Implement contract in "Physical or digital gold: simple insurance on Ergo"

[smallboxlabs]

Hi @kushti — I'd like to take this one (reserving via ErgoDevs/Ergo-Bounties).

From the forum post, I've implemented it as a self-contained example spec in
sc/shared/src/test/scala/sigmastate/utxo/examples/ (same shape as the other example
bounties): the insurance box holds the digital gold tokens, with R4 = insurance deadline
(height) and R5 = the insurance NFT id, and the script allows

• before the deadline: spending by any transaction that presents the insurance NFT in
  its inputs — the digital gold can then go to any address ("either party can present the
  NFT"), and
• after the deadline: reclaim by the vault's key,

with prove/verify tests covering both paths plus the negative cases (no NFT, reclaim too
early, NFT presented after expiry, wrong NFT).

The implementation is green across tree versions (tested on Scala 2.13 and 2.12) and I
can open the PR right away.

Two quick scope questions:

1. Is an in-repo example spec the right deliverable here, or do you also want a
   standalone repo / write-up?
2. I close the redemption window exactly at the deadline (the two paths never overlap,
   so the vault can't be front-run after expiry — but an NFT holder who misses the
   deadline loses the claim). Is that the semantics you intended? Trivial to flip if not.

[smallboxlabs]

Implementation PR: #1183. Reservation: ErgoDevs/Ergo-Bounties#42.

[smallboxlabs]

I'm releasing my reservation on this one so it's free for anyone else who'd like to pick it up.

The implementation is still open as #1183 (green across the 2.11/2.12/2.13 + JS matrix) — happy for it to be merged, adapted, or closed at your discretion if it's useful. Thanks!