0747 — Throughput scenarios can disable message recording while retaining aggregate measurements

Context

Per-message JSON recording materially changes the throughput being measured. The user approved disabling it for throughput scenarios while preserving full recording for reliability scenarios. This supersedes the always-record policy in 0745; its other workload, environment, retention, and warmup decisions remain in force.

Decision

• Scenario.DisableMessageRecording defaults false. Set it true for throughput and max-throughput; existing reliability scenarios retain full records.
• Disabled mode bypasses construction and writing of per-message producer and handler records. Record cumulative counters once per second per process and stream/group, plus a final snapshot at graceful shutdown.
• Keep the existing roles, observer, checker, resource measurements, phase records, results, and run index. Rate calculations use actual sampled spans, summing independent process rates; missing or decreasing counters are errors.
• Keep attempted/committed/rejected/unknown and handler success/error counts. Disabled scenarios must declare an errors expectation. Handler totals and error checks describe loaded snapshots, not a per-message proof.
• Mark identity-based checks and schedule adherence unavailable in both JSON and printed results. Detailed latency is unavailable; never print zero latency as a measurement. A paced phase cannot claim all guards held when schedule adherence was unavailable.
• Record the flag in the declaration and verdict. A passing aggregate run proves only the checks that ran; it does not prove exactly-once handling, absence of message loss, or crash-recoverable evidence completeness.

Consequences

• Throughput runs avoid recorder disk traffic and large post-run ledger imports.
• Reliability and future failure scenarios keep the default full evidence.
• No alternative production-library behavior or public client API is introduced.
• Measurement endpoints exclude partial sampled intervals; aggregate throughput is an observed rate, not reconstruction of every message’s completion time.