refactor: use ConfigurationKeys.Telemetry.RootSessionId instead of pragma hacks

Re-add _DD_ROOT_DOTNET_SESSION_ID to supported-configurations.yaml so it
generates ConfigurationKeys.Telemetry.RootSessionId. RuntimeId.cs can now
use that constant directly — no RootSessionEnvVar const, no #pragma DD0012
suppression needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: khanayan123

tracer/src/Datadog.Trace/Configuration/supported-configurations.yaml

@@ -1571,6 +1571,15 @@ supportedConfigurations:
     documentation: |-
       Configuration key for whether telemetry metrics should be sent.
       <see cref="Datadog.Trace.Telemetry.TelemetrySettings.MetricsEnabled"/>
+  _DD_ROOT_DOTNET_SESSION_ID:
+  - implementation: A
+    type: string
+    default: null
+    product: Telemetry
+    const_name: RootSessionId
+    documentation: |-
+      Internal env var for propagating the root session ID to child processes.
+      Set automatically by the tracer at init time; not user-configurable.
   DD_TEST_MANAGEMENT_ATTEMPT_TO_FIX_RETRIES:
   - implementation: A
     type: int

tracer/src/Datadog.Trace/Generated/net461/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.Telemetry.g.cs

@@ -105,5 +105,11 @@ internal static class Telemetry
         /// <see cref="Datadog.Trace.Telemetry.TelemetrySettings.MetricsEnabled"/>
         /// </summary>
         public const string MetricsEnabled = "DD_TELEMETRY_METRICS_ENABLED";
+
+        /// <summary>
+        /// Internal env var for propagating the root session ID to child processes.
+        /// Set automatically by the tracer at init time; not user-configurable.
+        /// </summary>
+        public const string RootSessionId = "_DD_ROOT_DOTNET_SESSION_ID";
     }
 }

tracer/src/Datadog.Trace/Generated/net6.0/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.Telemetry.g.cs

@@ -105,5 +105,11 @@ internal static class Telemetry
         /// <see cref="Datadog.Trace.Telemetry.TelemetrySettings.MetricsEnabled"/>
         /// </summary>
         public const string MetricsEnabled = "DD_TELEMETRY_METRICS_ENABLED";
+
+        /// <summary>
+        /// Internal env var for propagating the root session ID to child processes.
+        /// Set automatically by the tracer at init time; not user-configurable.
+        /// </summary>
+        public const string RootSessionId = "_DD_ROOT_DOTNET_SESSION_ID";
     }
 }

tracer/src/Datadog.Trace/Generated/netcoreapp3.1/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.Telemetry.g.cs

@@ -105,5 +105,11 @@ internal static class Telemetry
         /// <see cref="Datadog.Trace.Telemetry.TelemetrySettings.MetricsEnabled"/>
         /// </summary>
         public const string MetricsEnabled = "DD_TELEMETRY_METRICS_ENABLED";
+
+        /// <summary>
+        /// Internal env var for propagating the root session ID to child processes.
+        /// Set automatically by the tracer at init time; not user-configurable.
+        /// </summary>
+        public const string RootSessionId = "_DD_ROOT_DOTNET_SESSION_ID";
     }
 }

tracer/src/Datadog.Trace/Generated/netstandard2.0/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.Telemetry.g.cs

@@ -105,5 +105,11 @@ internal static class Telemetry
         /// <see cref="Datadog.Trace.Telemetry.TelemetrySettings.MetricsEnabled"/>
         /// </summary>
         public const string MetricsEnabled = "DD_TELEMETRY_METRICS_ENABLED";
+
+        /// <summary>
+        /// Internal env var for propagating the root session ID to child processes.
+        /// Set automatically by the tracer at init time; not user-configurable.
+        /// </summary>
+        public const string RootSessionId = "_DD_ROOT_DOTNET_SESSION_ID";
     }
 }

tracer/src/Datadog.Trace/Util/RuntimeId.cs

@@ -5,15 +5,13 @@
 
 using System;
 using System.Threading;
+using Datadog.Trace.Configuration;
 using Datadog.Trace.Logging;
 
 namespace Datadog.Trace.Util
 {
     internal static class RuntimeId
     {
-        // Internal propagation env var, not user-configurable — intentionally not in ConfigurationKeys.
-        internal const string RootSessionEnvVar = "_DD_ROOT_DOTNET_SESSION_ID";
-
         private static readonly IDatadogLogger Log = DatadogLogging.GetLoggerFor(typeof(RuntimeId));
         private static string _runtimeId;
         private static string _rootSessionId;
@@ -38,17 +36,15 @@ private static string GetRuntimeIdImpl()
 
         private static string GetRootSessionIdImpl()
         {
-#pragma warning disable DD0012 // internal propagation env var, not user-configurable
-            var inherited = EnvironmentHelpers.GetEnvironmentVariable(RootSessionEnvVar);
-#pragma warning restore DD0012
+            var inherited = EnvironmentHelpers.GetEnvironmentVariable(ConfigurationKeys.Telemetry.RootSessionId);
             if (!string.IsNullOrEmpty(inherited))
             {
                 Log.Debug("Inherited root session ID from parent: {RootSessionId}", inherited);
                 return inherited;
             }
 
             var rootId = Get();
-            EnvironmentHelpers.SetEnvironmentVariable(RootSessionEnvVar, rootId);
+            EnvironmentHelpers.SetEnvironmentVariable(ConfigurationKeys.Telemetry.RootSessionId, rootId);
             return rootId;
         }
     }

tracer/test/Datadog.Trace.Tests/TracerTests.cs

@@ -572,7 +572,7 @@ public void RootSessionId_DefaultsToRuntimeId()
         public void RootSessionId_SetsEnvVar()
         {
             var rootSessionId = Datadog.Trace.Util.RuntimeId.GetRootSessionId();
-            Environment.GetEnvironmentVariable(Datadog.Trace.Util.RuntimeId.RootSessionEnvVar)
+            Environment.GetEnvironmentVariable(ConfigurationKeys.Telemetry.RootSessionId)
                        .Should().Be(rootSessionId);
         }