Guarantee monotonic event sequence numbers across nested contract invocations #1799

Problem

Indexers need a reliable ordering signal when several nested operations emit events in one transaction.

Scope

Define the sequence-number source and update it at one auditable boundary. Ensure failed operations do not create gaps that look like committed state.

Acceptance criteria

• Committed events have strictly monotonic ordering within a transaction.
• Failed operations do not publish committed sequence entries.
• Nested-call integration tests verify ordering.

Validation

Compare emitted events with final storage state across single and batch operations.