Boost Harvester (technical)

XdcNftBoostHarvester is the small, non-upgradeable contract that funds the XDC NFT vault's Synthetix-style boost accumulator. It exists because the underlying PrimeStakedXDC_V3 vault is non-upgradeable — the boost stream had to live in an external pump rather than being routed inside the V3 vault itself.

Live address: 0x3bEdb37FC873F64BEeFCA551b3A836e59fc18DeA. The harvester holds the only address granted FEE_ROUTER_ROLE on the NFT vault — i.e. it's the only contract allowed to call notifyBoost. Arbitrary XDC sends to the NFT vault cannot corrupt boost accounting.

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What the harvester does

┌────────────────────────────────────────────────────────────────────────┐
│                     XDC sources (treasury / NAV)                        │
│                                                                         │
│   feed(amount) ────────► forwards native XDC directly to notifyBoost   │
│                                                                         │
│   harvest(sharesToRedeem) ──► redeemWithQueue on psXDC v3 vault ──►    │
│       …queued or instant XDC payout…                                    │
│       forwardPending() picks up the XDC and pushes notifyBoost          │
└────────────────────────────────────────────────────────────────────────┘
                                  │
                                  ▼
            XdcNftStakingVault.notifyBoost(amount) payable
                  - converts XDC → psXDC v3 shares via depositNative
                  - bumps rewardPerWeightStored += sharesMinted * 1e18 / totalWeight
                  - reverts if totalWeight == 0

Two funding paths

Path	Function	When to use it
Direct push	feed(uint256 amount) payable	Treasury wants to push native XDC straight into the boost stream — fastest, no queue involved.
NAV harvest	harvest(uint256 sharesToRedeem)	The treasury seeded the harvester with psXDC v3 shares as principal; redeeming those shares captures the NAV gain over time. The XDC may arrive instantly (buffer covers it) or via the queue.
Drain pending	forwardPending()	Anyone can call this. Any native XDC sitting on the harvester (e.g. from a queued harvest that just settled) is forwarded into notifyBoost.

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How the boost reaches NFT holders

When notifyBoost(x) runs on the NFT vault:

1. The vault calls psXDC_v3.depositNative{value: x}(x, vault) and receives sharesMinted of psXDC v3.

2. rewardPerWeightStored += sharesMinted * 1e18 / totalWeight.

3. Every staked NFT's pending boost immediately reflects the new value, proportional to the NFT's weight: earned = info.shares * (rewardPerWeightStored - info.rewardIndex) * weight / 1e18.

4. notifyBoost reverts if totalWeight == 0 — pushing boost into an empty vault is a no-op so the value can't be wasted.

The Synthetix-style accumulator means timing doesn't matter as long as your NFT was staked when the push happened. You can claim now, later, or never — the value stays attributed to you.

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Why an external harvester

The original idea was to fund boost from psXDC v3's own NAV. That would have required adding a "fee skim" feature to the V3 vault. But the V3 vault is deliberately non-upgradeable (regular constructor, no proxy) so there is no way to change its logic after deployment. The harvester sidesteps this:

• Treasury seeds the harvester with psXDC v3 shares (or directly with XDC).

• When NAV has grown, the harvester redeems a portion via redeemWithQueue (going through the same instant-vs-queued path every user sees) and the resulting XDC funds the boost.

• The V3 vault itself never needs to know about boost; the harvester is the chokepoint.

The trade-off is that the harvester needs to be funded by an operator. The cadence is an operational choice — typically a weekly batch is cheapest gas-wise, daily is the friendliest UX. Either way, every notifyBoost emits a public event indexed by the subgraph so the UI can derive a trailing 30-day boost APR.

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Roles & safety

Role	Holder	Why
DEFAULT_ADMIN_ROLE (vault)	Protocol multisig	Master switch — can grant/revoke other roles
FEE_ROUTER_ROLE (vault)	XdcNftBoostHarvester	The only address allowed to call notifyBoost
PAUSER_ROLE (harvester)	Protocol multisig	Emergency stop

The NFT vault deliberately has no receive() function — there is no way to "donate" XDC into the boost accumulator outside notifyBoost. This means random XDC sent to the vault cannot corrupt the accounting; only the harvester's notifyBoost calls move rewardPerWeightStored.

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What integrators can read

The harvester is a no-secret contract — every operation is on-chain and emits events. Useful read paths:

• BoostNotified(uint256 amountIn, uint256 sharesMinted, uint256 rewardPerWeightStored, uint256 totalWeight) on the NFT vault — each push.

• BoostFed / BoostHarvested / BoostForwarded on the harvester (or equivalent) — operational events.

• earned(tokenId) view on the NFT vault — pending boost for a specific NFT.

The subgraph at xdc-nft-v3-indexer provides aggregated entities including BoostNotification, per-NFT boost stats, and the DailyProtocolSnapshot series used by the UI.

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Pause behaviour

When the NFT vault is paused (PAUSER_ROLE), stake / withdraw / claim revert, but notifyBoost continues to work — this is intentional: boost flow keeps accruing even during an emergency pause, so users don't lose value during ops windows.

When the harvester itself is paused, no new pushes happen but pending value on the NFT vault is unaffected.

→ Reward Model: Base NAV + Boost → Staking Mechanics → Smart Contract Reference