Add spec for AlwaysRecord sampler

Author: majanjua-amzn

CHANGELOG.md

@@ -13,6 +13,8 @@ release.
 
 - Deprecate Zipkin exporter document and make exporter implementation optional.
   ([#4715](https://github.com/open-telemetry/opentelemetry-specification/pull/4715/))
+- Add spec for `AlwaysRecord` sampler
+  ([#4699](https://github.com/open-telemetry/opentelemetry-specification/pull/4699))
 
 ### Metrics
 

spec-compliance-matrix.md

@@ -90,6 +90,7 @@ formats is required. Implementing more than one format is optional.
 | [Support W3C Trace Context Level 2 randomness](specification/trace/sdk.md#traceid-randomness) | X | - |  |  |  |  |  |  |  |  |  |  |
 | [TraceIdRatioBased sampler implements OpenTelemetry tracestate `th` field](specification/trace/sdk.md#traceidratiobased) | X | - |  |  |  |  |  |  |  |  |  |  |
 | [CompositeSampler and built-in ComposableSamplers](specification/trace/sdk.md#compositesampler) | X | - |  |  |  |  |  |  |  |  |  |  |
+| [Sampler: AlwaysRecord](specification/trace/sdk.md#alwaysrecord) | X |  |  |  |  |  |  |  |  |  |  |  |
 
 ## Baggage
 

specification/trace/sdk.md

@@ -41,6 +41,7 @@ weight: 3
       - [Compatibility warnings for `ProbabilitySampler`](#compatibility-warnings-for-probabilitysampler)
     + [ParentBased](#parentbased)
     + [JaegerRemoteSampler](#jaegerremotesampler)
+    + [AlwaysRecord](#alwaysrecord)
     + [CompositeSampler](#compositesampler)
       - [ComposableSampler](#composablesampler)
         * [GetSamplingIntent](#getsamplingintent)
@@ -603,6 +604,25 @@ The following configuration properties should be available when creating the sam
 [jaeger-remote-sampling-api]: https://www.jaegertracing.io/docs/1.41/architecture/apis/#remote-sampling-configuration-stable
 [jaeger-adaptive-sampling]: https://www.jaegertracing.io/docs/1.41/architecture/sampling/#adaptive-sampling
 
+#### AlwaysRecord
+
+**Status**: [Development](../document-status.md)
+
+`AlwaysRecord` is a sampler decorator that ensures every span is passed to
+the `SpanProcessor`, even those that would normally be dropped. It does this
+by converting `DROP` decisions from the wrapped sampler into `RECORD_ONLY`,
+decisions, allowing processors to see all spans without sending them to
+exporters. This enables accurate span-to-metrics processing.
+
+* Root sampler returns `DROP` -> AlwaysRecord returns `RECORD_ONLY`
+* Root sampler returns `RECORD_ONLY` -> AlwaysRecord returns `RECORD_ONLY`
+* Root sampler returns `RECORD_AND_SAMPLE` -> AlwaysRecord returns `RECORD_AND_SAMPLE`
+
+Required parameters:
+
+* `root(Sampler)` - The sampler being wrapped; it provides the original
+sample/drop decision that AlwaysRecord modifies.
+
 #### CompositeSampler
 
 **Status**: [Development](../document-status.md)