docs(pipeline): align delivery contracts and verification requirements

openspec/changes/telecom-cdr-pipeline/specs/observability/spec.md

@@ -30,3 +30,14 @@ All pipeline services SHALL emit log lines formatted as structured JSON to stdou
 #### Scenario: Operational event logged
 - **WHEN** any service logs an event (info, warning, or error)
 - **THEN** the log output is a single-line JSON object containing at minimum `timestamp` (ISO 8601 UTC), `level` (INFO, WARN, ERROR), `service` (`ingestion-api` or `processing-worker`), `raw_id` (record identifier or null), and `event` (short descriptive string)
+
+### Requirement: Measured and truthful telemetry
+Metrics SHALL count acknowledged destination operations, measure Kafka timestamp-to-write latency and periodically update partition lag from committed offsets and high watermarks.
+
+#### Scenario: Delivery and scrape
+- **WHEN** records complete storage and metrics are scraped
+- **THEN** latency observations and partition gauges are populated, failed DLQ attempts do not increment counters, and label values are correctly escaped
+
+#### Scenario: Failure diagnostics
+- **WHEN** a structured event is logged
+- **THEN** preserve the human-readable message including failure details alongside the event identifier