Function backgroundExecution

Deny a write-class connector call whose arguments carry the LLM _background key, whatever its value. This complements createConnector's hard _background argument rejection, which uses the same presence test.

Mastra's standard agent loop removes a truthy _background from the arguments before dispatch, so a call Mastra runs as a background task carries no key and this evaluator cannot see it; the connector wrapper refuses that call instead. Read-only calls pass. A call whose sideEffect is not a SideEffect member is denied, since it cannot be shown to be read-only. Register the evaluator through ConnectorPolicies.evaluators.