Method emit_session_fork_kg

atomic-core/src/pristine/txn/write/session_kg.rs:448–466

Emit the fork-derivation triple: child session `prov:wasDerivedFrom` parent session, with the fork boundary in edge metadata. Public because the fork boundary is decided at the repository layer (`Repository::fork_session`); the turn/session emission stays internal to the index paths.

(
        &mut self,
        child_session_id: &str,
        parent_session_id: &str,
        fork_turn: u32,
        parent_manifest: &Hash,
    )

    /// (`Repository::fork_session`); the turn/session emission stays internal
    /// to the index paths.
    pub fn emit_session_fork_kg(
        &mut self,
        child_session_id: &str,
        parent_session_id: &str,
        fork_turn: u32,
        parent_manifest: &Hash,
    ) -> PristineResult<()> {
        self.upsert_kg_edge(
            &KgEdge::new(
                session_node_id(child_session_id),
                session_node_id(parent_session_id),
                predicate::WAS_DERIVED_FROM,
            )
            .with_metadata(serde_json::json!({
                "fork_turn": fork_turn,
                "parent_manifest": parent_manifest.to_base32(),
            })),
        )
    }
}