Evaluation Diagnostics

Reference model for evaluation diagnostics emitted through observability surfaces and shadow-evaluation mismatch callbacks.

Diagnostic Core Fields

Field	Meaning
namespaceId	Namespace where evaluation occurred.
featureKey	Evaluated feature identifier.
configVersion	Active configuration version metadata (if provided).
mode	Evaluation mode (NORMAL, SHADOW, explain/diagnostic modes).
durationNanos	Evaluation latency in nanoseconds.
value	Typed evaluated value returned by the engine.
decision	Decision category and associated match details.

Decision Categories

Decision category	Meaning
Registry disabled	Namespace kill-switch forced default return.
Inactive	Feature-level inactive state forced default return.
Rule	One rule matched and produced value.
Default	No rule matched; declared default returned.

Shadow Mismatch Model

When using shadow evaluation, mismatch callbacks include:

• featureKey
• baseline diagnostics snapshot
• candidate diagnostics snapshot
• mismatch kinds (VALUE, DECISION)

Operational Use

• Alert on mismatch rates during migrations.
• Correlate decision classes with rollout incidents.
• Track evaluation latency by namespace and feature.

Next Steps

• Migration from Legacy
• Migration and Shadowing Theory