ottyl/tickets/001-param-declarations.md

001 — Param declarations

Summary

Implement the ParamDeclaration slice of the primary index: users can declare how a named parameter is derived from a log line (e.g. deriving a timestamp different from the ingestion timestamp, or a log level), and the engine stores/serves those declarations.

Scope

• IndexKey::ParamDeclaration { name } and a matching DataValue variant for the declaration body (a regex against the raw log text, plus how the capture maps to a MetricPrimitive — reuse RegexToMetricPrimitiveMatcher / MetricPrimitiveKind from data_value.rs, which already exist but are unused).
• Engine message(s) to add/list/remove a param declaration.
• Validate declared regexes at declaration time (reject invalid regex / unknown primitive kind up front rather than failing per-log later).
• No derivation/backfill against existing logs yet — that's 002 / 003, since metrics are what actually get indexed into buckets. This ticket is just the declaration storage + validation.

Acceptance criteria

• Declaring a param with a valid regex + capture group succeeds and is retrievable.
• Declaring a param with an invalid regex or referencing a non-existent capture group is rejected with a clear error, not silently stored.
• Declarations sit in their own contiguous range of the BTreeMap (ParamDeclaration between LogParamSplit and ParamMetricSplit), per the IndexKey ordering in the README.

Depends on

None — this is foundational.