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docs/observability/telemetry-propagation-51-001.md

@@ -14,7 +14,8 @@
 
 ## HTTP middleware
 - Accept `traceparent`/`tracestate`; reject/strip vendor-specific headers.
-- Propagate `tenant`, `actor`, `imposed-rule` via `Stella-Tenant`, `Stella-Actor`, `Stella-Imposed-Rule` headers.
+- Propagate `tenant`, `actor`, `imposed-rule` via `x-stella-tenant`, `x-stella-actor`, `x-stella-imposed-rule` headers (defaults configurable via `Telemetry:Propagation`).
+- Middleware entry point: `app.UseStellaOpsTelemetryContext()` plus the `TelemetryPropagationHandler` automatically added to all `HttpClient` instances when `AddStellaOpsTelemetry` is called.
 - Emit exemplars: when sampling is off, attach exemplar ids to request duration and active request metrics.
 
 ## gRPC interceptors
@@ -28,7 +29,8 @@
 ## Metrics helper expectations
 - Golden signals: `http.server.duration`, `http.client.duration`, `messaging.operation.duration`, `job.execution.duration`, `runtime.gc.pause`, `db.call.duration`.
 - Mandatory tags: `tenant`, `service`, `endpoint`/`operation`, `result` (`ok|error|cancelled|throttled`), `sealed` (`true|false`).
-- Cardinality guard: drop/replace tag values exceeding 64 chars; cap path templates to first 3 segments.
+- Cardinality guard: trim tag values to 64 chars (configurable) and replace values beyond the first 50 distinct entries per key with `other` (enforced by `MetricLabelGuard`).
+- Helper API: `Histogram<double>.RecordRequestDuration(guard, durationMs, route, verb, status, result)` applies guard + tags consistently.
 
 ## Determinism & offline posture
 - All timestamps UTC RFC3339; sampling configs controlled via appsettings and mirrored in offline bundles.