0706 — Portable export validation and read health

Context

Superseded by [0707], which narrows validation to export compatibility.

The SDK producer replacement [0705] is complete. The approved contract [0682] requires visible read failure and collection-local family rejection without preventing healthy families from exporting.

Decision

• Validate retained families before conversion using the pinned upstream UnderscoreEscapingWithSuffixes metric and attribute translation. Configure the convenience Prometheus reader with the same strategy.
• Reject the whole original-name family for conflicting kind/unit, ambiguous translated metric or attribute names, reserved names, or unusable kind/unit. Built-ins must match their declaration. Reserve exporter health names even against retained built-ins, Vulkan’s custom namespace, target_info, and otel_scope_ metadata names; reserve double-underscore attribute names too.
• Return source.read_success (VK0102) as 1 on successful reads, including empty results. Return measurements.rejected (VK0103), counting each omitted retained row once. Both are attribute-free collection-local gauges, never persisted.
• On read failure, return read-success 0 together with the source error; omit retained measurements and the rejection count. Partial rejection returns no collection error, so healthy families remain eligible for periodic export.
• Log VK0104 per rejected family with original metric_names and detail, never measurement values or metadata. Reevaluate every collection without a cache.

Consequences

ManualReader retains read-success 0 alongside the error, and Prometheus can serve it with HTTP 200. PeriodicReader skips export on collection errors; its full lifecycle verification remains a separate checkpoint. Portable validation also applies to non-Prometheus readers. Translation dependencies stay pinned; no new version or module is introduced.