[epic] metric_map completeness: source metrics → existing OTel data in Elasticsearch

[shmsr]

Why this epic

Migrating Grafana (and Datadog) dashboards onto existing OTel data already in Elasticsearch fails on vocabulary, not on the query engine. Source dashboards use Prometheus/cAdvisor (or Datadog) metric names; Elastic stores dotted OTel semantic-convention fields via OTLP. Bridging them is the metric_map program started by #305.

Live evidence (origin/main @ 5da0dd2, ES seeded with real OTel k8s fields)

Real Grafana Kubernetes / Compute Resources / Pod dashboard (16 panels), --field-profile otel --es-url --preflight:

• Baseline, no map: 0/16 panels. Every metric missing in required_target_contract.json even though the equivalent dotted OTel field exists (57 fields discovered).
• With map, Class-1 renames applied: container_memory_working_set_bytes → container.memory.working_set and container_memory_rss → container.memory.rss flipped to confirmed.
• Class-2 not applied: container_network_{receive,transmit}_bytes_total → k8s.pod.network.io {direction} stayed missing; recorded as a gap, k8s.pod.network.io never emitted.
• Gaps not surfaced: metric_map_gaps()/warnings() are populated but no artifact reads them.
• Recording rules (5) and cross-data-stream limits/requests have no single-rename target.

Scope / sub-issues

• [Grafana] Add a source→OTel metric-name mapping layer (otel profile currently passes metric names through verbatim) #309 — metric-name mapping layer: Class-1 (done via Add shared metric mapping primitives #305), a shipped default map, and the otlptranslator forward-index auto-suggest generator. (Data-stream targeting moved to [Grafana] Multi-target panel fusion keeps only one target; support multi-series overlays incl. attribute-split and cross-data-stream sources #311.)
• [metric_map] Emit Class-2 entries (transform / attribute_filter / unit_scale) instead of recording gaps #314 — emit Class-2 entries (attribute_filter → WHERE, transform → rate, unit_scale → scaling); until then, surface gaps/warnings in report + panel notes.
• [Grafana] Multi-target panel fusion keeps only one target; support multi-series overlays incl. attribute-split and cross-data-stream sources #311 — multi-series overlays incl. attribute-split and cross-data-stream / per-metric target data stream.
• [Grafana] Detect Prometheus recording-rule series with no target field; flag instead of emitting silently-empty panels #310 — detect Prometheus recording rules (no target field) and flag instead of empty panels.
• [Grafana] Apply metric_map in the native PromQL path (currently bypassed) so operators can keep PromQL output and rename metrics #315 — apply metric_map in the native PromQL path (currently bypassed).

Related (separate source track)

• [Datadog] Rate/counter temporality & unit correctness on Agent to OTel collector switch #308 — Datadog rate/temporality/unit correctness (same Class-2 machinery, Datadog source).