SharedArc
A shared USDC stream for collectives on Arc: one rate, N shares, live runway.
SharedArc is an MIT-licensed building block, not a SaaS. A pre-funded pool pays USDC per second, split among
members by mutable integer shares. Joining, leaving or re-weighting mid-stream is one O(1) write that touches
nobody else's storage. When the pool runs dry the stream freezes by itself and resumes on the next deposit, so
it can never owe more than it holds — and the owner can never touch what members have already earned.
It has three parts: one immutable singleton contract (DripPool), a TypeScript SDK that mirrors the accrual
math so a UI ticks per second without RPC calls, and a static reference app, "Collective Payroll".
Status: live on Arc mainnet since 2026-09-18. DripPool is deployed at
0x92b8fdB2c457b64d4510aC980A84283356D8A44f
and verified on Sourcify (exact match). All ten proof rows are recorded below. Unaudited and
experimental: keep amounts small.
Name: the project was called ArcDrip until 2026-09-18 and was renamed to avoid a clash with an unrelated
product of the same name on Arc. That is why the CREATE2 salt is keccak256("arcdrip.v1"); the contract,
its address and every recorded transaction are unchanged.
What it does
An owner creates a pool with a ratePerSecond for the whole pool and gives each member an integer number
of shares. Anyone can deposit USDC into it. From then on every member's claimable balance grows every second,
in proportion to their shares, with no keeper and no per-period transaction. A member withdraws their own
balance, or anyone can push a payout to every member in one transaction ("Pay everyone").
The pool is the unit of accounting, so the treasury has one number to watch: balance / rate is the
runway, in days, for the whole collective at once.
Guarantees enforced on-chain
| Guarantee | Mechanism |
|---|
| Earned is earned | owed (streamed and not yet withdrawn) is untouchable. withdrawUnstreamed and cancel are bounded by balance − ceilDiv(owed, 1e12). Invariant I4 asserts that no owner action — setRate, setShares on another member, withdrawUnstreamed, cancel, ownership transfer — ever decreases any member's claimable. |
| Never owes more than it holds | _accrue caps elapsed time at available / rate. That cap is the freeze: an empty pool stops streaming instead of promising. Invariant I2: owed ≤ balance × 1e12. |
| No back-pay after a freeze | Frozen time is never recovered. A deposit resumes streaming from the deposit's own timestamp. |
| Rounding always favours the pool | Every division floors. Members collectively receive at most what was streamed; the remainder is dust that stays in owed (bounded below 1 wad = 1e-18 USDC per accrual by MAX_TOTAL_SHARES). Invariant I1 bounds the dust, and a fuzz run (I5) checks every payout against an exact-rational reference model. |
| O(1) membership changes | Accumulated-index accounting: setShares settles one member and updates totalShares. No loop over members, so the cost of adding the 100th member is the cost of adding the first. |
| Payouts go to the member | withdrawFor and withdrawForBatch are permissionless, but funds always go to the member's payout address, never to the caller. A member with no gas still gets paid by someone else. |
| One blocked member cannot stall the rest | withdrawForBatch wraps each transfer in a try: on a revert or a false return it restores that member's pending and the pool's owed/balance and emits WithdrawSkipped. The batch never reverts because of one member. |
| Money never streams into the void | With totalShares == 0 nothing accrues and no funds are consumed. |
|
Non-goals
No token, no yield, no fees, no admin key over the contract, no upgradeability. Not a Sablier clone: there
are no per-recipient streams, only pools with shares. Not a splitter: nothing is distributed on arrival,
only over time. The owner's ability to pause, re-weight or cancel the future stream is deliberate — this is a
payroll, not an escrow.
How the math works
One pool stores ratePerSecond (wad/s), totalShares, balance (USDC units), owed (wad already streamed
and not yet withdrawn) and accIndex (wad per share, ×1e18). A member stores shares, index and pending.
Internal amounts are wad = USDC units × 1e12, so 1 USDC/month is 385,802,469,135 wad/s rather than 0.
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