add support for detecting OpenAI Codex usage of the dotnet CLI

.github/policies/resourceManagement.yml

@@ -114,9 +114,13 @@ configuration:
             This PR has been labeled with `Area-Telemetry`. Please ensure that any telemetry changes in this PR
 
             * comply with the [published guidance](https://learn.microsoft.com/dotnet/core/tools/telemetry#data-points)
+
             * are added to the [repo-local telemetry documentation](./documentation/project-docs/telemetry.md)
+
             * get a matching .NET Docs issue raised to document the telemetry changes
+
               * Go to https://learn.microsoft.com/dotnet/core/tools/telemetry
+
               * Scroll down to the bottom and click the 'Open a documentation issue' link to create an issue with pre-filled details
       - requestReview:
           reviewer: dsplaisted

documentation/project-docs/telemetry.md

@@ -61,7 +61,7 @@ Every telemetry event automatically includes these common properties:
 | **Telemetry Profile** | Custom telemetry profile (if set via env var) | Custom value or null |
 | **Docker Container** | Whether running in Docker container | `True` or `False` |
 | **CI** | Whether running in CI environment | `True` or `False` |
-| **LLM** | Detected LLM/assistant environment identifiers (comma-separated) | `claude`, `cursor`, `gemini`, `copilot`, `generic_agent` |
+| **LLM** | Detected LLM/assistant environment identifiers (comma-separated) | `claude`, `cursor`, `gemini`, `copilot`, `generic_agent`, `codex` |
 | **Current Path Hash** | SHA256 hash of current directory path | Hashed value |
 | **Machine ID** | SHA256 hash of machine MAC address (or GUID if unavailable) | Hashed value |
 | **Machine ID Old** | Legacy machine ID for compatibility | Hashed value |

src/Cli/dotnet/Telemetry/LLMEnvironmentDetectorForTelemetry.cs

@@ -7,13 +7,15 @@ internal class LLMEnvironmentDetectorForTelemetry : ILLMEnvironmentDetector
 {
     private static readonly EnvironmentDetectionRuleWithResult<string>[] _detectionRules = [
         // Claude Code
-        new EnvironmentDetectionRuleWithResult<string>("claude", new AnyPresentEnvironmentRule("CLAUDECODE")),
+        new EnvironmentDetectionRuleWithResult<string>("claude", new BooleanEnvironmentRule("CLAUDECODE")),
         // Cursor AI
-        new EnvironmentDetectionRuleWithResult<string>("cursor", new AnyPresentEnvironmentRule("CURSOR_EDITOR")),
+        new EnvironmentDetectionRuleWithResult<string>("cursor", new BooleanEnvironmentRule("CURSOR_EDITOR")),
         // Gemini
         new EnvironmentDetectionRuleWithResult<string>("gemini", new BooleanEnvironmentRule("GEMINI_CLI")),
         // GitHub Copilot
         new EnvironmentDetectionRuleWithResult<string>("copilot", new BooleanEnvironmentRule("GITHUB_COPILOT_CLI_MODE")),
+        // OpenAI Codex
+        new EnvironmentDetectionRuleWithResult<string>("codex", new BooleanEnvironmentRule("CODEX_THREAD_ID")),
         // (proposed) generic flag for Agentic usage
         new EnvironmentDetectionRuleWithResult<string>("generic_agent", new BooleanEnvironmentRule("AGENT_CLI")),
     ];

test/dotnet.Tests/TelemetryCommonPropertiesTests.cs

@@ -242,6 +242,7 @@ public void TelemetryCommonPropertiesShouldContainSessionId(string? sessionId)
             { new Dictionary<string, string> { { "GEMINI_CLI", "false" } }, null },
             { new Dictionary<string, string> { { "GITHUB_COPILOT_CLI_MODE", "false" } }, null },
             { new Dictionary<string, string> { { "AGENT_CLI", "false" } }, null },
+            { new Dictionary<string, string> { { "CODEX_THREAD_ID", "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa" } }, "codex" },
             { new Dictionary<string, string>(), null },
         };