A chain step that references a derived evidence is now expanded at compile
time, keeping the engine a flat edge-traversal evaluator:
- DIRECT evidence step -> renamed to its underlying relation
(member_of(user,*g){ group_read(g,doc) } where group_read = can_view
becomes step 'can_view').
- CHAIN evidence step -> its steps are spliced into the parent chain
(a sub-path flattens into the linear source->...->object traversal).
- Any other evidence type (defeasible/logical/comparator) as a step is a
compile-time error: it is a condition, not an edge traversal.
- Cycles and self-references through chain steps are compile-time errors
(the existing composition cycle guard now covers steps).
Rigor: oracle campaign gains a chain_step_composition construct; illegal
mutations gain a non-lowerable-chain-step case. Fixture suites updated to
retarget the self-recursive 'canRead/canAccess/...' terminals (an unsupported
recursion pattern that now fails loudly) to an any-typed 'reachable' fact,
preserving the nested-pattern parsing intent.
John Dvorak
2dc478f5a3