The driver's streaming path reports ModelUsage(0, 0) even though the vendor stream carries token counts (e.g. the driver's processStreamingChunk never reads chunk usage).
The driver's failed non-streaming ChatResult ('failedResult' mode) does not populate
errorInfo, so retry/failover layers get no structured error classification.
The catalog of contract deviations this suite knows how to pin. Each kind flips a specific assertion from the ideal contract to the driver's actual behavior.