Module stage 

StepStage — transactional COW staging for one step() (10 buckets).

Every commit-conditional write the kernel performs during a step is buffered here; on commit, Instance::apply_stage drains in canonical canonical order; on rollback, the stage is dropped without effect.

Buckets (10):

1. state_ops — entity/component mutations
2. events — KernelEvent emissions (kernel-level drain)
3. schedule_deltas — scheduler add/cancel
4. pending_signals — outbound IPC (kernel routes post-commit)
5. id_counters — monotonic ID counter advances
6. ledger_delta — ResourceLedger updates
7. inflight_refs_delta — drain-refcount per RouteId (signed delta)
8. wall_remainder_delta — sub-tick time accumulator advance
9. local_tick_delta — logical tick advance
10. observer_eviction_pending — observers slated for eviction