rules_injected tool call — a rule file (e.g. AGENTS.md)
was injected into the agent’s context.
Discriminated by the required rule_display_name field: only
rules_injected events carry cognition.ai/ruleDisplayName. It is a
non-Option String with no #[serde(default)], so serde’s untagged enum
dispatch only picks this variant when the incoming _meta actually has
cognition.ai/ruleDisplayName. Mirrors the pattern used by
ReportBlockerMeta and CognitionRecordingStoppedMeta.