Add LLM detection section to .NET CLI telemetry documentation

Co-authored-by: meaghanlewis <[email protected]>

Author: Copilot

docs/core/tools/telemetry.md

@@ -91,6 +91,7 @@ The telemetry feature collects the following data:
 | >=6.0.104     | Hashed CompileListCount used for build (MSBuild property) |
 | >=6.0.104     | Hashed _ReadyToRunCompilationFailures used for build (MSBuild property) |
 | >=6.0.300     | If the CLI was invoked from a Continuous Integration environment. For more information, see [Continuous Integration Detection](#continuous-integration-detection).|
+| >=9.0.100     | If the CLI was invoked from an LLM agent environment and the detected agent type. For more information, see [LLM Detection](#llm-detection).|
 | >=7.0.100     | Hashed PublishAot used for build (MSBuild property) |
 | >=7.0.100     | Hashed PublishProtocol used for build (MSBuild property) |
 | >=8.0.100     | Hashed TargetPlatformIdentifier used for build (MSBuild property) |
@@ -190,6 +191,16 @@ The full list of environment variables, and what is done with their values, is s
 | TEAMCITY_VERSION | TeamCity | Check if present and non-null |
 | JB_SPACE_API_URL | JetBrains Space | Check if present and non-null |
 
+## LLM Detection
+
+To detect if the .NET CLI is running in the context of an LLM agent environment, the .NET CLI probes for the presence and values of several environment variables that LLM agents and AI coding assistants set.
+
+The following table shows the environment variables used for detection and the agent type that is reported. Similar to CI detection, the actual values of these environment variables are never collected—only used to identify the agent type.
+
+| Variable(s) | Agent Type | Action |
+| ----------- | ---------- | ------ |
+| COPILOT_AGENT_ACTION, COPILOT_CLOUD_ENVIRONMENT | GitHub Copilot | Check if all are present and non-null |
+
 ## Avoid inadvertent disclosure of information
 
 .NET contributors and anyone else running a version of the .NET SDK that they built themselves should consider the path to their SDK source code. If a crash occurs while using a .NET SDK that is a custom debug build or configured with custom build symbol files, the SDK source file path from the build machine is collected as part of the stack trace and isn't hashed.