Run: slither . --solc solc-0.8.28 --exclude-dependencies. Baseline: 25 INFO findings, 0 High/Medium. Triage:

• divide-before-multiply (_updateDebts): intentional — dust to payer, conservation invariant holds (tested).
• reentrancy-no-eth/benign (settleDebt): mitigated — nonReentrant + immutable OZ ERC20 without hooks.
• calls-loop: all calls to trusted sibling contracts, bounded ≤ 50 members.
• reentrancy-events: events after calls to trusted contracts only.
• assembly (array resize), low-level-calls (checked ETH call), pragma (OZ ^0.8.20 compiles under one solc), naming-convention (UPPER immutables): accepted style.
• missing-inheritance (ExpenseManager vs IExpenseManager): deferred, rename-only value.
• Not in CI (needs Python+solc runners) — run locally before mainnet.

• Contracts are custodial for ETH (TrustToken holds mint payments) and for accounting (debts/balances). No oracles, no external calls except ETH transfers (redeem, withdraw) and TRUST.transferFrom (settleDebt).
• Owner powers: TrustToken.withdraw (all ETH), set-once wiring (setExpenseManager, setDebtSimplifierContract). No upgrade proxy — owner cannot change accounting logic, only drain ETH and set wiring once.
• Frontend holds no secrets: frontend/.env contains public deployment addresses only; private keys never touch the app (MetaMask signs locally).

• mint/redeem/withdraw (TrustToken) and settleDebt (ExpenseManager) carry OZ nonReentrant (storage-based guard, no EIP-1153 dependency). redeem additionally burns before the ETH call (checks-effects-interactions).
• Ownership is two-step (Ownable2Step): transferOwnership + acceptOwnership. Tested in test/TrustToken.test.ts ("Ownership Transfer").
• settleDebt updates state after transferFrom but under the guard; with the trusted immutable TRUST_TOKEN (plain OZ ERC20, no receiver hooks) there is no callback vector — guard is defense in depth.

• EQUAL/PERCENTAGE truncate; remainder is absorbed by the payer (credited only the distributed sum). Invariant sum == 0 holds; payer silently overpays dust (< n wei per expense). Documented, tested in test/DustConservation.test.ts.
• redeem reverts on tokenAmount % MINT_RATE != 0 (Amount not multiple) instead of silently burning dust value. ethAmountFull == 0 also reverts (Token amount too small).

• 2% of the ETH value stays in the contract (REDEMPTION_FEE_PERCENT = 2); only owner can withdraw it. The token side never truncates (non-multiples revert); only (ethAmountBeforeFee * 2) / 100 can truncate sub-wei dust.

• initializeGroupBalances callable only by GroupManager; groups created before wiring keep implicit zero balances (mapping default) — safe.
• joinGroup relies on implicit zero balance for newcomers — safe but implicit.
• leaveGroup/deleteGroup debt scans are O(n²) external getDebt calls; DoS-safe at 50 members, revisit if the cap rises.