feat: LVGA payout bridge + stable-value (stability-vault) variant

[tiero]

Summary

The LVGA productization layer of the cross-chain bridging work: a merchant-payment bridge-out from Arkade to a SwissLedger (EVM) LVGA liquidity pool, plus a stable-value variant that backs the spending balance with a Bitcoin-collateralized, oracle-marked CHF claim.

Split out from the general bridge research (#56) so this PR is just the LVGA-specific pieces. Depends on nothing from #56 — the contracts use only primitives already on master.

Contracts

• examples/bridge/wlvga_payout.ark (WlvgaPayout) — the Arkade payout leg, two modes:

  • payOut() (two parties, default) — transfer the BTC-backed wLVGA claim to the LVGA liquidity provider (LP), so the LP is compensated in BTC for the LVGA it releases. LVGA is transfer-restricted / one-way (never redeemed for wLVGA), so the BTC side and the LP can be distinct entities.
  • burnOut() (same party) — burn the wLVGA; only solvent when the LP also received the BTC at mint (integrated market maker).
  • Both authorize the payee with the merchant's secp256k1 key via checkSigFromStack (mirrored by ecrecover on the pool) and pin an OP_RETURN commitment protocolTag ‖ merchantEvmAddr ‖ num2bin(amount, 8); replay bounded by burnNonce.

• examples/bridge/swissledger_pool.md — spec for the EVM pool contract that auto-releases LVGA (Flavor A: a trusted reporter attests the burn; ecrecover + whitelist + paid[nonce] keep it contained to liveness, not correctness). Includes byte layout, the little-endian / recoverable-ECDSA integration notes, and a reference Solidity sketch.

• examples/stability/stability_lvga_payout.ark (StabilityPayout) — stable-value variant. seekerPayout() settles a BTC-collateralized, oracle-marked CHF claim directly as a merchant LVGA payment: verifies the CHF/BTC oracle price and the merchant invoice, routes the seeker's BTC entitlement to the LP, and commits payoutCHF. The merchant receives a stable amount regardless of BTC moves; price risk sits with the vault provider, not the bridge. Set lpPk = providerPk for a single delta-neutral market maker.

• examples/bridge/lvga_bridge.md — overview doc tying the flow together.

Design notes

• One key, two chains. A single merchant secp256k1 key is verified by checkSigFromStack on Arkade and ecrecover on the EVM pool over the same message.
• Correct economics for transfer-restricted LVGA. LVGA never round-trips, so the LP's compensation is the BTC-backed claim (payOut transfer), and the CHF/BTC exposure is isolated in the stability vault's funded provider role — not dumped on the bridge or the user.
• pubkey/signature stay strictly inside checkSigFromStack, so hashed/committed fields concat via OP_CAT and the digest matches off-chain signing and the EVM reconstruction byte-for-byte.

Testing

• tests/examples/wlvga_payout.rs (5) + tests/examples/stability_lvga_payout.rs (4).
• cargo fmt --check clean; full examples suite green.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Ttf3oxgKCxBsYWJrQYfUfE

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