feat: Account Recycler contract with bonding curve pricing

[aglichandrap]

Account Recycling Contract

Implements Convex-Dev/bounties#10 — Account Recycling Contract with bonding curve pricing.

Features

• Deposit: Users can deposit accounts they control to the recycling market
• Buy: Purchase available accounts at bonding curve price
• Sell: Sell accounts back to the market at a spread (85% of buy price)
• Bonding Curve: Price increases when fewer accounts available, decreases when more
• Account Clearing: Deposited accounts are cleared (undef, set-controller nil)
• Security: Controller verification, fund checks, trust-based withdrawal

Bonding Curve Model

• Base price: 1000 Copper
• Price increases as availability decreases
• 15% spread between buy and sell price
• Min/Max price bounds (100 - 1,000,000 Copper)

Files

• convex-core/src/main/cvx/convex/lab/account-recycler/actor.cvx — Main contract
• convex-core/src/test/cvx/test/convex/account-recycler.cvx — Tests

Security Considerations

• Only account controller can deposit/sell
• Contract balance checked before buy-back
• Trust-based fund withdrawal
• Account environment cleared on deposit

[mikera]

(Claude Comment) Thanks @aglichandrap — this one is genuinely interesting, and we would like to take it further than a lab actor. Recycling cleared accounts addresses a real resource-efficiency need, and the bonding-curve market is a neat mechanism for it.

Direction we are considering: making this a core service, possibly with a newly allocated early-address account, installed as part of a protocol migration (the v1 or v2 network upgrade could carry it). That raises the design bar accordingly — the parts needing careful work are:

• Account clearing: the eval-as + undef sweep must provably leave no residual state, controller bindings, or callable capabilities on a recycled account — a buyer must get a genuinely clean account, and a depositor must not be able to retain a backdoor.
• Controller semantics during deposit/hold/sale, including interaction with delegated control.
• Bonding-curve arithmetic bounds and rounding (all in Copper, no overflow at the extremes).

Two practical asks meanwhile: (1) this branch currently also contains unrelated bigint core-function changes (Core.java / Symbols.java, same content as #575) — please strip those so the PR is the pure actor + tests; (2) keep it targeting convex/lab/ for now — promotion to a core service address happens via the migration design, not this PR.

Happy to iterate on the design here or in an issue. Nice work.