[Benchmark]: Measure governance materialization output

[rian-be]

Summary

Benchmark governance side effect and decision materialization so persisted outputs and request-level decision records stay visible over time.

Goal

Measure the overhead of materializing governance side effects, decisions, and execution-linked output that downstream consumers read from audit, history, or request stores.

Problem

Governance already records side effects, decisions, and execution-linked output, but those materialization paths are not benchmarked as a dedicated runtime surface.

Without a benchmark for governance materialization behavior, changes in side effect copying, decision projection, or persisted output shape can quietly add overhead without being visible in runtime measurements.

Scope

• Benchmark side effect materialization on governance results and requests
• Benchmark decision materialization for governance request outcomes
• Benchmark execution-linked output materialization where it is part of the governance contract
• Keep the benchmark focused on governance output materialization rather than provider internals
• Reuse existing governance benchmark helpers where they already exist
• Make scenario names explicit about the materialization path being measured

Design Expectations

• The benchmark should measure a real governance output flow rather than a toy loop.
• Side effect and decision output should remain visible where possible.
• Helper code should stay local to the benchmark project.
• Scenario names should make the materialization path obvious.

Suggested Measurements

• request with side effects materialized for persistence
• request decision output materialized for downstream consumption
• execution-linked governance output materialized for audit or history

Acceptance Criteria

• Governance side effect and decision materialization is benchmarked as a distinct governance scenario
• Side effect output cost is visible in the benchmark results
• Decision output cost is visible in the benchmark results
• The benchmark remains centered on governance runtime behavior

Non-Goals

• This issue does not change governance runtime behavior
• This issue does not add provider-specific persistence benchmarks
• This issue does not optimize materialization prematurely
• This issue does not add full integration or load testing

Notes

This issue is a child of the governance benchmark umbrella #73.