Invariant suite handler uses legacy EIP-191 signatures, silently reverts every position creation, yields zero security signal

The Foundry invariant suite at evm_protocol/test/invariant/VaultInvariant.t.sol declares ten invariant_* properties exercised through PositionHandler.sol. The suite reports green on every campaign run, but produces no security signal because its handler builds signatures with legacy EIP-191 packed format while the contract requires EIP-712 typed data:

// PositionHandler._signCreatePosition (lines 470-491), legacy EIP-191 packed:
bytes32 messageHash = keccak256(abi.encodePacked("CREATE_POSITION", positionSeed, user, marketId, ...));
bytes32 ethSignedHash = keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", messageHash));

// SignatureLib.verifyCreatePositionSignature requires EIP-712:
bytes32 structHash = keccak256(abi.encode(CREATE_POSITION_TYPEHASH, ...));
bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));

Different digests result in recovered signer not equal to appAdmin1 / appAdmin2, triggering an InvalidSignature revert. The revert is swallowed by the try/catch block in PositionHandler.createPosition (line 130), so the fuzzer treats the call as non-reverting and continues. createdPositionKeys stays empty across every run, and every position-iterating invariant is vacuously satisfied. Only invariants that check immutable state (AdminAddressesNeverZero, ExternalContractsNeverZero, VersionIsOne) or pause-toggle ghost state carry real signal.

The correct EIP-712 signing helpers (_signCreatePositionWithKey, _signFinalizeSettleWithKey) already exist in test/helpers/SignatureHelpers.sol and are used by every passing unit test. The handler simply does not inherit them.

Have PositionHandler inherit SignatureHelpers (which extends Test) instead of importing Test directly, override _getVaultAddress() to return address(vault), delete the local packed-signature helpers, and route signing through the inherited EIP-712 functions. Add a campaign-level liveness assertion (afterInvariant: positionCount > 0) so a regression that re-introduces silent signature failures fails a hard check instead of being absorbed by the catch block.

Fixed. Invariant handler now inherits SignatureHelpers and signs via the EIP-712 helpers; campaign-level liveness assertion guards against silent regression.