Export Activity.StatusDescription as otel.status_description custom property

[Copilot]

Description

Implements export of Activity.StatusDescription as a custom property otel.status_description in telemetry sent to Azure Monitor, addressing the gap where status descriptions set via Activity.SetStatus(statusCode, description) were being ignored.

Changes

• RequestData.cs and RemoteDependencyData.cs: Added conditional export of Activity.StatusDescription as custom property when present
• Tests: Added coverage for both presence and absence of status descriptions in RequestData and RemoteDependencyData

The property key follows OpenTelemetry semantic conventions and leverages existing truncation/validation logic.

Example Usage

using var activity = activitySource.StartActivity("MyOperation", ActivityKind.Server);
activity.SetStatus(ActivityStatusCode.Error, "Request failed due to timeout");
// StatusDescription now exported to Azure Monitor as otel.status_description

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Original prompt

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This section details on the original issue you should resolve

<issue_title>[FEATURE REQ] Support Activity.StatusDescription in Exporter</issue_title>
<issue_description>### Library name

Azure.Monitor.OpenTelemetry.Exporter

Please describe the feature.

Support exporting Activity.StatusDescription as a custom property otel.status_description in telemetry.

OpenTelemetry suggest using Activity.SetStatus() to set status of trace. (https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/src/OpenTelemetry.Api/README.md#setting-status)
Currently the Exporter can use Activity.Status to determine the Success field, but the Activity.StatusDescription is totally ignored. The information of status description is missing in Azure telemetry. One possible way to keep this information would be adding custom property otel.status_description which matches the sematic convention of OpenTelemetry.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [FEATURE REQ] Support Activity.StatusDescription in Exporter #41057

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