D046 - Three observability channels

Status: decided Date: 2026-08-19

The developer log (tracing) says what the emulator is doing; the guest call recording holds every guest call and never goes through tracing; the run report is a versioned, bounded, machine-readable record per run. The run report is the contract; log prose is not.

Why: a log call per guest call would dominate the profile and change what it measures. A consumer grepping log prose breaks when a message is reworded. The report is an index - top-N, last-N, its own inputs embedded, a diff against the previous run - because a finite reader cannot consume a full trace.

Rejected:

• One channel for everything: volume and audience differ by orders of magnitude.
• Agents parsing logs: an unversioned API.