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The POST /v1/sponsor endpoint is DarkPool’s gas onramp. It uses Sui’s native sponsored-transaction protocol with no Enoki Portal allowlist, no third-party dependency, and the ability to sponsor any package. Both zkLogin and wallet users sign trades without holding any SUI.

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Why we shipped it

The user had configured Allowed Addresses in the Enoki Portal with the package IDs (wrong field; that section gates sender addresses, not Move targets), so every sponsorship attempt 403’d. Asking the user to redo the Portal config was both fragile and a third-party dependency. Self-sponsorship sidesteps it entirely. Enoki sponsorship stays as Strategy 1 for zk users. The user paid for the credits and we shouldn’t waste them when the Portal is correctly configured.

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Wire protocol

Chain enforces sender == user (their signature is mandatory). Gas comes from the sponsor.

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Abuse bounds

Three caps prevent a hostile PTB:
Env varDefaultBound
SPONSOR_MAX_GAS_BUDGET_SUI0.03Per-tx hard ceiling on gas budget
SPONSOR_PER_USER_DAILY_CAP_SUI0.5Per-sender daily cap (Redis-tracked)
SPONSOR_DAILY_CAP_SUI5Global daily cap
Redis keys sponsor:user:<addr>:<yyyy-mm-dd> and sponsor:global:<yyyy-mm-dd> use INCRBYFLOAT with EXPIRE-to-end-of-day. Worst case: one bad actor at the per-user cap drains 0.5 SUI/day, the global cap drains 5 SUI/day total. Both fit a hackathon budget.
PTB-command inspection (reject tx.gas references in TransferObjects and SplitCoins) is a v0.4 hardening follow-up.

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Frontend integration

packages/frontend/src/lib/wallet.ts is the three-strategy signer:
  1. Self-sponsor first. Works for both wallet and zk users. Sponsors any package.
  2. Enoki sponsorship. Zk users only, on SponsorUnavailableError.
  3. Direct execution. User pays gas (last resort).
All 11 sign call sites flow through useTxSigner() which encapsulates the cascade.

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GET /v1/sponsor

{
  "enabled": true,
  "sponsorAddress": "0x…",
  "perUserDailyCapSui": 0.5,
  "globalDailyCapSui": 5,
  "maxGasBudgetSui": 0.03
}
The UI uses this to decide whether to show the “Gas sponsored” badge.