[simplex]: ERC-4626 vault funding venue

[royvardhan]

Implements #939 — yield-venue funding via ERC-4626.

Adds a filler-wide ERC-4626 venue for sourcing and managing stablecoin liquidity. Any compliant vault (Aave stataToken, Morpho, an issuer yield vault) is a config entry — no protocol-specific code:

• Sourcing: when wallet balance is short on a fill, withdraw the deficit from the solver's vault position (vault.withdraw), prepended atomically before fillOrder in the same ERC-7821 batch; capped by vault.maxWithdraw. Wired into both the stable and FX strategies.
• Sweeping: a timer deposits wallet balance above a configured threshold into the vault (exact approve + deposit, batched in one ERC-7821 call), keeping the threshold liquid for fills.
• Shutdown: all vault positions are redeemed back to the underlying asset.
• Config: top-level [erc4626].vaults = [{ chain, vault, threshold? }]; the underlying asset is resolved on-chain from the vault.
• Renamed the basic strategy to stable.

[seunlanlege]

haven't looked at the code yet, but this should support hydrating free USDC/USDT balances at startup to aave & everytime its cumulative stablecoin free balance crosses some minimum threshhold.

[seunlanlege]

also do we check maxDeposit/maxWithdrawal before interacting with the vault?

[seunlanlege]

Inline review of the ERC-4626 vault funding venue. Two pre-existing concerns plus the two requested additions (maxDeposit check, redeemOnShutdown flag) are left as inline comments at the relevant sections.

Blocking-ish: (1) the [erc4626] vs [vault] config-key mismatch silently disables the feature for anyone following the docs; (2) the reservation (consumed) accounting looks like it leaks for evaluated-but-not-won orders and can degrade sourcing to zero over time — worth confirming. Everything else is polish. Nice use of maxWithdraw as the authoritative sourcing cap, and good atomic approve+deposit batching.

[seunlanlege]

Re-reviewed at 4f0421d — thanks, all four items from the last pass are addressed:

• ✅ Config key — now [vault] consistently across code, filler-config-example.toml, and docs (planner name also renamed "Vault").
• ✅ Reservation leak — replaced the monotonic consumed counter with TTL-bounded reservations; won bids release immediately on the realised position drop, lost bids expire. Good back-to-back-fill and TTL-expiry tests.
• ✅ maxDeposit clamp — added to the ABI and the sweep now deposits min(excess, maxDeposit), skipping when headroom < minSweep. Covered by two new tests.
• ✅ redeemOnShutdown — per-vault flag, defaults false (positions kept across restarts), honoured in redeemChain and documented in the example config. Tested both ways.

Also a nice unprompted catch: ordering the vault venue before the V4 LP for the FX strategy so stablecoins source from the treasury before draining (and perturbing the price of) a concentrated-liquidity position.

Two small non-blocking notes inline (TTL vs. slow cross-chain settlement; a benign FIFO-vs-expiry ordering nit in releaseReserved). LGTM otherwise.

[seunlanlege]

One follow-up design suggestion on the sweep config naming/semantics — non-blocking, details inline on VaultConfig and sweepChain. TL;DR: replace threshold (retained float) + minSweep (dust floor) with minBalance (floor to keep in wallet) + threshold (high-water trigger that sweeps down to minBalance). Drops minSweep entirely and gives clean hysteresis with two self-explanatory knobs.

[seunlanlege]

lets try to get tests passing & we can merge

[seunlanlege]

Simplex test failing