BOAW Phase 6B: Parallel Execution Engine Integration #258

Summary

Integrate the BOAW (Bag of Active Workers) sharded parallel execution into engine_impl.rs::apply_reserved_rewrites().

Context

Phase 6B is the culmination of the BOAW parallel execution architecture. The primitives were implemented in previous phases:

• Phase 1-5: TickDelta, GraphView, WarpOp emission, read-only execution
• Phase 6A: execute_parallel_sharded() with atomic shard claiming

This phase wires everything into the main engine loop.

Deliverables

• apply_reserved_rewrites() uses execute_parallel_sharded() internally
• Per-warp parallelism (rewrites grouped by warp_id)
• Configurable worker count via ECHO_WORKERS env var or EngineBuilder::workers(n)
• Fix non-determinism bug in view op ID generation (emit_view_op_delta_scoped())
• All tests pass including DIND golden hashes
• Tech debt documented in TECH-DEBT-BOAW.md

Related Docs

• docs/adr/ADR-0007-BOAW-Storage.md — full architecture
• docs/adr/PLAN-PHASE-6B-VIRTUAL-SHARDS.md — phase spec
• docs/adr/TECH-DEBT-BOAW.md — future work