Tool errors - Nito

Tool failures use the standard error envelope: an HTTP error before generation, or a chunk with a top-level error and finish_reason: "error" mid-stream.

Causes

Condition	Code
Web search or fetch on a model that does not advertise it	`invalid_request`
Duplicate tool aliases that resolve to the same server tool	`invalid_request`
Provider failure while a tool ran	`provider_error` (`502`) or `unavailable` (`503`)

Branch on error.code. Check the model’s capabilities before sending a tool.