Function plan_scc_rules 

pub fn plan_scc_rules(
    rules: &BTreeMap<String, Vec<Rule>>,
    base_relations: &RefRelationStore,
) -> Result<BTreeMap<String, Vec<RulePlan>>, PlanError>

Plan a mutually-recursive rule group with PR 8 transitive type inference engaged.

Mirrors the input shape: returns a BTreeMap<predicate, Vec<RulePlan>> where result[p][i] corresponds to rules[p][i]. Each rule’s verdict is computed after running infer_scc_predicate_schemas over the full group, so a recursive-only join key whose type is established only via inference is now flagged with super::Boundary::UnsupportedKeyType consistent with super::evaluate_scc_fixpoint_typed.

Why this exists separately from plan_rules

plan_rule / plan_rules type variables from base_relations only — they have no group context and can’t run inference. Without plan_scc_rules, a planner driving the per-rule API would mark even(X, Y) :- odd(X, Z), odd(Z, Y) as RulePlan::MultiwayCandidate even when odd’s schema (inferred via PR 8) propagates an unsupported type to Z — i.e., the planner and the SCC evaluator would disagree on the same fixture. PR 9 closes that gap.

Errors

Returns PlanError::InferenceConflict for cross-rule head-column conflicts detected during inference, PlanError::ConflictingVariableType for within-rule body conflicts (both layered the same way as super::evaluate_scc_fixpoint_typed), and PlanError::RuleHeadPredicateMismatch for misgrouped rules (rule’s head predicate ≠ its BTreeMap group key).

Structural-error precedence

Mirrors the super::evaluate_scc_fixpoint_typed pre-flight (PR 9): if any rule is misgrouped, the function returns PlanError::RuleHeadPredicateMismatch BEFORE running inference, so a misgrouped rule whose body would also produce inference conflicts surfaces the structural error first. This keeps planner and evaluator verdicts symmetric for every fixture class.