Each kind of system fails in its own way. We start every project by writing that failure down, then build and test against it.
Fig. 01 — One spec per kind of system
Fails when
Must always hold
// Shares are never worth more than the assets behind them. function invariant_solvency() public { assertGe(asset.balanceOf(address(vault)), vault.convertToAssets(vault.totalSupply())); }
Illustrative tests, one per kind of system.
Four kinds of team, each with its own definition of what must not go wrong.
Whatever the system, the work starts the same way. Here is one rule, followed all the way through.
Before any code, in plain words, in the specification you sign off.
“Shares can never be worth more than the assets behind them.”SPEC.md · I-1
The sentence becomes an invariant the fuzzer attacks with random call sequences.
function invariant_solvency() { assertGe(assets, owed()); }
Every pull request runs it. A finding reaches you as a failing test, then a fix.
$ forge test [PASS] invariant_solvency() ok · runs on every PR
Illustrative example from a vault engagement.
Five kinds of system we build most often, and the one failure each is designed around.
Money moves in one transaction, and any path you did not think of is someone else's profit.
AMMs, vaults, staking, lending primitives and routers.
Solvency and share-price invariants under long random call sequences.
Related service// Shares are never worth more than the assets behind them. function invariant_solvency() public { assertGe(asset.balanceOf(address(vault)), vault.convertToAssets(vault.totalSupply())); }
The token must obey rules the law already set: who may hold it, and who may move it.
Permissioned tokens, claims registries, issuer consoles and distributions.
// Only verified investors can ever hold the token. function invariant_holdersVerified() public { for (uint256 i; i < holders.length; i++) assertTrue(registry.isVerified(holders[i])); }
Keys are the product. One compromised device should never be enough.
Threshold signing, policy engines, web and mobile clients.
// No path signs with fewer than two approvals. test("cannot sign alone", async () => { const req = await policy.request(transfer); await approve(req, alice); await expect(signer.sign(req)).rejects.toThrow("2 of 3"); });
Supply, voting power and treasury access are where incentives turn into attacks.
ERC-20 systems, vesting, governors, timelocks and treasuries.
// Votes count at the snapshot, so a flash loan adds nothing. function invariant_noFlashVotes() public { uint256 snap = gov.proposalSnapshot(proposalId); assertEq(gov.getVotes(attacker, snap), votesAt[snap]); }
An agent that can write to your systems needs the same care as a contract.
Retrieval, scoped tool-calling agents and approval queues.
# No write reaches the ERP without a human approval. def test_write_needs_approval(agent, erp, queue): agent.run("mark order 4411 as shipped") assert erp.writes == [] assert queue.pending[0].action == "update_order"
Describe the product and the risk you are worried about. We will tell you what we would build, and what we would not.