G. Error Handling

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Feature	Status	Notes
require(condition)	✅	Maps to NeoVM ASSERT.
require(condition, "msg")	✅	ASSERT with message.
require(condition, CustomError(...))	✅	Error name and arg count preserved in NeoVM THROW message.
assert(condition)	✅	Maps to NeoVM ASSERT.
revert()	✅	Maps to NeoVM ABORT.
revert("message")	✅	ABORT with message.
revert CustomError(...)	✅	Named revert with arguments.
Custom error definitions	✅	error X(...) parsed and used in revert statements.
try / catch	✅	NeoVM TRY/ENDTRY structured exception handling.
try with return binding	✅	try f() returns (uint r) { ... } supported.
Multiple catch clauses	✅	Lowered with EVM-canonical 4-byte selector guards (Task #103). catch Panic(uint256) matches 0x4e487b71, catch Error(string) matches 0x08c379a0, catch (bytes) binds the raw envelope. User-defined named error clauses retain the legacy permissive ISTYPE guard.

Partial error handling details

Multiple catch clauses — Task #103 switched the dispatcher to EVM-canonical selector matching. catch Panic(uint256) and catch Error(string) now guard on the 4-byte keccak selector (0x4e487b71, 0x08c379a0) at the head of the revert envelope, decoding code / msg via StdLib.abiDecode and SUBSTR. User-defined named catches (e.g. catch CustomErr(uint c)) retain the pre-#103 ISTYPE guard until a follow-up extends selector-based routing to custom errors.

// ✅ Recommended — single catch clause
try target.someFunction() returns (uint256 result) {
    // success
} catch (bytes memory reason) {
    // handle any failure
}

// ⚠️ Works but with caveats — multiple catch clauses
try target.someFunction() returns (uint256 result) {
    // success
} catch Error(string memory reason) {
    // string exceptions routed here
} catch (bytes memory lowLevelData) {
    // everything else
}

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