Module inference 

Transitive type inference across SCC predicates.

Closes the PR 5 policy gap: where a join-key vertex was anchored only through SCC-recursive atoms, the typed gate previously left it untyped under “unknown ≠ unsupported.” This module propagates types through the rule graph — body atoms type variables, head atoms back-propagate to head-predicate columns, iterate to fixpoint — so the typed gate has full type information when it consults super::analyze_typed.

Where inference is engaged

Only the group-aware typed entry points engage inference:

• super::evaluate_scc_fixpoint_typed runs inference once at entry, then types each rule’s body using the inferred schemas plus base_relations.
• super::evaluate_fixpoint_typed treats target_predicate as a single-element rule group and runs the same inference.

The single-rule entry points retain the base-only typing policy because they have no SCC structure to propagate over:

• super::evaluate_rule_typed takes one rule.
• super::plan_rule / super::plan_rules plan per-rule.

Callers that want SCC-aware planning should drive super::evaluate_scc_fixpoint_typed directly or build their own inference pass via infer_scc_predicate_schemas.

Conflict layering

Inference detects only back-propagation conflicts: e.g., predicate p’s column 0 is U32 from rule A’s head and Symbol from rule B’s head → InferenceError::ConflictingPredicateColumnType. Within-rule body conflicts (variable X typed U32 in one body atom and Symbol in another) stay in the existing super::typed flow and surface as super::RefEvalError::ConflictingVariableType. Each conflict type is detected at exactly one layer.

Cyclic-only predicates

When an SCC has no base anchor anywhere (e.g., a(X) :- b(X), b(X) :- a(X) with no rule referencing base_relations), every column converges to None. The typed gate must NOT reject such rules: the policy narrows from “unknown ≠ unsupported” to “unknowable-after-inference ≠ unsupported.” Locked by cyclic_only_predicate_still_passes_typed_gate_locked_policy.

Strict-correctness behavior change

Fixtures whose base-relation schemas disagreed but whose actual rows happened to agree at runtime were previously silent (the typed gate types each body atom independently). They now surface as InferenceError::ConflictingPredicateColumnType when back-propagating to a head predicate. That is a strict correctness win, not a regression — fixtures with internally contradictory schemas are now caught before evaluation rather than silently corrupting downstream comparisons.

Enums

InferenceError

Errors surfaced by infer_scc_predicate_schemas.

Functions

infer_scc_predicate_schemas

Infer per-predicate schemas for a rule group via constraint propagation through the rule graph.

Type Aliases

InferredSchemas

Per-predicate inferred schema. Vec length equals the head arity; each element is Some(t) if inference established the column’s type, or None if the column remains unknowable (e.g., cyclic-only predicate, or a head term whose body atoms don’t type the corresponding variable).