Prometheus exporter + Grafana dashboards as code

[rubinder]

Problem

The platform measures a great deal and exports none of it. make monitor persists every metric to ops.monitor_results and routes alerts to ops.alert_log (src/ops/runner.py, src/ops/alerts.py), with robust median/MAD baselines and history (ADR-0007). But the only way to see any of it is to run a make target and read stdout, or query the Iceberg table by hand.

That is the gap between "this platform has checks" and "this platform is operated". A monitoring story that ends at a terminal transcript is the thing the README's own framing — data quality as an engineered property, not a dashboard someone occasionally checks — argues against.

Proposed change

A thin export layer over data that is already persisted. No new measurement.

• src/ops/exporter.py: read the latest run from ops.monitor_results and ops.alert_log and render Prometheus text-format metrics. Batch jobs write a .prom file for the node_exporter textfile collector — no Pushgateway, no always-on process, consistent with the repo's offline-by-default posture.
• Metric surface, labelled by table / monitor / kind:
  • adp_monitor_value — the observed metric
  • adp_monitor_baseline_median — the trailing median it was judged against
  • adp_monitor_status — 0 ok / 1 warn / 2 breach
  • adp_arrival_lag_days, adp_arrival_status
  • adp_agent_findings_total{severity=...}
  • adp_promotions_blocked_total
  • adp_run_timestamp_seconds
• dashboards/ as code: one Grafana JSON dashboard + Prometheus alert rules, provisioned by a docker-compose.yml that brings up Prometheus + Grafana only (no Kafka, no ClickHouse).

Constraints

• make all, make monitor, make agent and make test must keep working with nothing running. The exporter writes a file; it must never require a scrape target to exist. Docker is strictly opt-in, and uv sync && uv run make all from a clean clone stays true.
• Cardinality stays bounded: labels are table/monitor/kind, never row values or IDs.
• The dashboard is committed as JSON and loaded by provisioning config, not clicked together in the UI.

Acceptance

• make monitor emits a valid Prometheus text-format file; a test parses it and asserts one series per monitor with the right labels.
• docker compose up brings up Prometheus + Grafana with the dashboard already provisioned, and no other service.
• An alert rule fires on a breach, demonstrated by make drift-demo (README transcript, with the sequence stated).
• Every make target still runs with docker stopped, and CI does not gain a service dependency.
• An ADR records why textfile-collector over Pushgateway.