Tech debt: remaining engine type safety and performance refactors

[ehotting]

Remaining items from #475 (Core Rust Engineering Review)

The high-impact, low-risk items were resolved in PRs #484 and #489. These remaining items are architectural refactors that require careful ownership restructuring.

Medium — Performance

Hot-path parameter clone reduction

• evaluate_article_with_service (service.rs) double-clones the parameter BTreeMap
• Each recursion level in evaluate_internal_traced (engine.rs) clones the full parameter map again
• Fix: Accept parameters by reference; only clone when transferring ownership to RuleContext::new

Arc for resolution cache hits

• Cache hits (service.rs) deep-clone two full BTreeMap<String, Value> (outputs + output_provenance)
• Fix: Wrap cached values in Arc<BTreeMap> so cache hits are O(1) clone

Medium — Idioms

Rc<RefCell<TraceBuilder>> → &mut TraceBuilder

• service.rs, context.rs, engine.rs — engine is single-threaded per execution
• Rc<RefCell> adds heap allocation + runtime borrow checking for no benefit
• Fix: Pass Option<&mut TraceBuilder> through the call chain. Requires restructuring the TraceGuard drop-based pop pattern.

Newtype IDs (LawId, ArticleNumber, BwbId)

• law_id, article_number, bwb_id are all plain String across engine, pipeline, harvester, corpus
• Compiler can't catch mix-ups (passing a bwb_id where a law_id is expected)
• Fix: Introduce newtypes with Deref<Target=str>, Display, Serialize/Deserialize. Ripples across all packages.

Low

• output_index uses null-byte sentinel in HashMap key (resolver.rs:74) — use (String, String) tuple key instead
• Operation::name() and ActionOperation::operation_name() duplicate all name strings — unify via strum or delegation