Detect API schema drift before it reaches wallet prompts

A provider can add fields harmlessly or change one field's meaning in a way that breaks execution. Contract tests should distinguish those cases before the application opens a wallet prompt.

Define the boundary you depend on

Validate required field types, amount units, chain identity and response variants. Check semantic relationships such as the request amount matching the normalized quote and an unavailable result lacking executable state.

Allow documented optional fields and compatible additions. Reject missing execution-critical fields. A parser that fails on every new metadata key is brittle; a parser that defaults a missing recipient to an empty address is unsafe.

Choose observation traffic carefully

Use provider-supported preview or read-only endpoints for routine canaries. The KyberSwap EVM specification distinguishes ordinary route previews from an execution-intent endpoint. Monitoring should respect that distinction rather than consuming firm liquidity solely to test uptime.

Keep canary frequency within the application's documented access policy. Commercial plan limits belong in configuration, not hardcoded assumptions inside the parser test.

Record changes for review

Retain a sanitized sample, provider version and the assertion that failed. Classify transport failure, provider rejection, schema drift and semantic mismatch separately. This prevents a temporary outage from being misdiagnosed as a code migration.

Pair live observation with deterministic fixtures. Live results reveal current behavior; fixtures let the team reproduce how its code handles a known response without depending on current market liquidity.

Gate only the affected capability

If transaction construction changes unexpectedly, disable that execution mode while preserving history and unaffected read paths. Do not keep submitting by accepting arbitrary fields, and do not remove all transaction tracking because new quotes are paused.

A contract test is an early-warning system for the integration boundary. It does not replace deployment validation, simulation or settlement reconciliation.