[sdk]: lock StreamingYieldVault deposits during vesting

[seunlanlege]

What

Stops new depositors from joining a StreamingYieldVault mid-tranche and skimming yield meant for the holders who were already in. Deposits are now confined to the window between tranches.

Changes

• Deposits/mints disabled while a tranche vests. maxDeposit/maxMint return 0 during vesting, so deposit/mint revert with the standard ERC4626ExceededMaxDeposit/ERC4626ExceededMaxMint. New capital can only enter after a tranche fully vests and before the next addYield.
• Guaranteed deposit window. addYield must now wait MIN_WINDOW (2h) past the vest end, reverting with DepositWindowOpen(closesAt) until then. This guarantees a deposit window every cycle regardless of how promptly the keeper runs, independent of an off-chain clock.
• VEST 23h → 22h, giving a 24h minimum cadence (VEST + MIN_WINDOW) with a guaranteed 2h window.
• Added nextYieldAt() view (close of the window / earliest next addYield).

Why vesting is still needed

Vesting remains the primary anti-snipe defense: it time-weights yield so momentary presence around a recognition event captures nothing, which is what keeps the open deposit window safe. The deposit lock is a complementary fairness rule (no mid-tranche joiners), not a replacement.

Tests

Foundry suite updated and green (25 passing): deposit/mint revert while vesting, deposits open across the whole window, maxDeposit/maxMint reflect the lock, the window can't be squeezed shut by an eager keeper, and an end-to-end check that a window depositor earns the next tranche but none of the current one.

Docs

streaming-yield-vault.mdx synced to the new behaviour (deposit lock, MIN_WINDOW, nextYieldAt, DepositWindowOpen, cadence guidance).